This specification covers materials, fabrication, installation, quality assurance, field testing, and cleaning for unit masonry construction in buildings and structures. Unit masonry within this standard means construction assembled from factory-produced units — concrete masonry units, clay brick, concrete brick, calcium silicate units — laid in mortar with or without grout and reinforcement. The standard applies to load-bearing walls, shear walls, non-load-bearing partitions, exterior veneer, pilasters, columns, and retaining walls of unit masonry construction.
Masonry is a composite system, and the performance of the completed assembly depends on the interaction of every component: units, mortar, grout, reinforcement, ties, anchors, flashing, and movement joints must all be properly selected, detailed, and installed. A single deficient component — improperly proportioned mortar, missing or blocked weep holes, omitted control joints — can compromise an otherwise sound assembly. This standard treats the system as a whole and provides requirements at the component and the assembly level.
All masonry construction shall comply with TMS 402/602-22, Building Code Requirements and Specification for Masonry Structures, and with the adopted edition of the International Building Code (IBC) Chapter 21. Where these standards conflict, the more stringent requirement governs unless the Engineer of Record directs otherwise in writing. Where the contract documents show more restrictive requirements than this specification, the contract documents govern.
Coordinate masonry work with the following related standards and scopes. Reinforcing steel procurement and handling shall comply with Concrete Reinforcement. Where masonry work is integrated with concrete structure, coordinate with Cast In Place Concrete. Insulation installed in masonry cavities or against masonry backup shall comply with Building Thermal Insulation. Where masonry serves as backup for roofing or waterproofing systems, coordinate with Membrane Roofing and Below Grade Waterproofing.
All materials and construction shall comply with the latest edition of the following standards as adopted by the Authority Having Jurisdiction. Where a specific edition year is shown on the contract documents, that edition governs.
| Standard | Title |
|---|---|
| TMS 402/602-22 | Building Code Requirements and Specification for Masonry Structures |
| IBC Chapter 21 | Masonry |
| ASTM C90 | Standard Specification for Loadbearing Concrete Masonry Units |
| ASTM C55 | Standard Specification for Concrete Brick |
| ASTM C129 | Standard Specification for Nonloadbearing Concrete Masonry Units |
| ASTM C216 | Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale) |
| ASTM C652 | Standard Specification for Hollow Brick (Hollow Masonry Units Made from Clay or Shale) |
| ASTM C62 | Standard Specification for Building Brick (Solid Masonry Units Made from Clay or Shale) |
| ASTM C270 | Standard Specification for Mortar for Unit Masonry |
| ASTM C476 | Standard Specification for Grout for Masonry |
| ASTM C144 | Standard Specification for Aggregate for Masonry Mortar |
| ASTM C150 | Standard Specification for Portland Cement |
| ASTM C207 | Standard Specification for Hydrated Lime for Masonry Purposes |
| ASTM C91 | Standard Specification for Masonry Cement |
| ASTM C1329 | Standard Specification for Mortar Cement |
| ASTM C404 | Standard Specification for Aggregates for Masonry Grout |
| ASTM C615 | Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement |
| ASTM A706 | Standard Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement |
| ASTM A951 | Standard Specification for Steel Wire for Masonry Joint Reinforcement |
| ASTM A153 | Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware |
| ASTM A1008 | Standard Specification for Steel, Sheet, Cold-Rolled, Carbon, Structural, High-Strength Low-Alloy |
| ASTM A580 | Standard Specification for Stainless Steel Wire |
| ASTM C1314 | Standard Test Method for Compressive Strength of Masonry Prisms |
| ASTM C780 | Standard Test Method for Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry |
| ASTM C1019 | Standard Test Method for Sampling and Testing Grout |
| ASTM C67 | Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile |
| ASTM C140 | Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units |
The Contractor shall submit the following for the Architect's and Engineer's review before procurement, mixing, or installation begins. No masonry work shall proceed until the corresponding submittal has been reviewed and returned without exception or with exceptions noted and resolved.
Product data shall be submitted for every masonry unit type, mortar material, grout material, joint reinforcement, wall tie and anchor system, through-wall flashing, weep system, and movement joint filler. Product data shall include the manufacturer's documentation of material compliance with all applicable ASTM standards, physical properties, and installation requirements.
Samples shall be submitted for each type of masonry unit to be used, including each color, texture, and size. Samples shall represent the full range of variation expected in the delivered product. A minimum of five units per type shall be submitted and, once accepted, retained on site as the standard for comparison during delivery inspection.
Where a mock-up is required by the contract documents, the mock-up submittal shall identify the proposed location, dimensions, unit types, mortar joint profile and color, and the proposed installation date. The mock-up procedure is described under Quality Assurance.
Mix designs shall be submitted for mortar and grout, identifying the cementitious materials, aggregates, admixtures, and the specification method (proportion or property) used to establish compliance with ASTM C270 or ASTM C476.
The Contractor shall provide the following at substantial completion before masonry work is accepted.
Certified test reports for all field-sampled prism tests, mortar samples, and grout samples, signed by the testing laboratory, including test methods, sampled locations, sample ages at test, measured values, acceptance criteria, and pass/fail determinations, shall be submitted. Corrective actions taken for failed tests shall be documented and re-test results included.
Operation and maintenance data describing recommended inspection intervals, recommended cleaning methods by unit type, and the location and type of all expansion and control joints shall be submitted for the Owner's records.
Masonry installation shall be performed by masonry contractors with demonstrated experience in the type of masonry specified. Journeyman masons shall have a minimum of five years of experience with comparable masonry construction. The masonry foreman directly supervising the work shall have a minimum of seven years of experience. The Contractor shall provide a list of at least three comparable projects completed within the previous five years upon request.
A pre-construction conference shall be held before masonry work begins. Attendees shall include the Contractor's masonry superintendent, the masonry subcontractor's project manager, the Architect, the Structural Engineer of Record, the Special Inspector, and the Owner's representative. Topics shall include: the mix design review and approval status, cold and hot weather contingency plans, the mock-up schedule, the special inspection program, joint reinforcement and vertical bar placement procedures, grouting procedure and lift heights, and flashing and weep installation sequence.
The Contractor shall construct a mock-up panel before beginning production masonry work. The mock-up demonstrates the Contractor's ability to achieve the specified appearance and workmanship and establishes the standard for the Owner's and Architect's review of color, texture, mortar joint profile, joint tooling, and workmanship quality.
The mock-up panel shall be built at the project site using the same materials, equipment, and personnel as will be used in production work. It shall incorporate a sample of the through-wall flashing and weep system, the specified joint profile, and where joint reinforcement is required, a section showing the joint reinforcement placement. The mock-up shall be reviewed and accepted in writing by the Architect before production work begins. The mock-up panel shall be maintained in place throughout the project and used as the quality standard for comparison. It shall not be demolished until directed by the Architect in writing, and not before substantial completion.
Masonry construction shall be subject to special inspection in accordance with IBC Chapter 17 and the Quality Assurance Program established in TMS 402/602, Article 1.6. The level of inspection — Level A, Level B (Continuous), or Level C — shall be as indicated on the contract documents and in the Statement of Special Inspections. Where not specifically indicated, Level B inspection shall apply to all engineered masonry in buildings assigned to Seismic Design Category C or higher.
The Special Inspector shall verify that masonry units, mortar materials, and grout materials are as specified; that mortar joint thickness and tooling comply with this specification; that reinforcement is placed as shown on the structural drawings; that cells to be grouted are clean and free of debris and mortar droppings; and that grouting procedures comply with the accepted procedure. The Special Inspector shall report nonconformances to the Contractor and the Architect immediately.
Masonry units shall be tested to verify compliance with the specified standard before or upon delivery. Verification shall be by manufacturer's certification accompanied by test reports from an independent testing laboratory for each production run, or by testing of samples from each delivery in accordance with ASTM C140 (concrete masonry units) or ASTM C67 (clay masonry units).
Where compressive strength prism testing is the basis for the specified masonry compressive strength f'm, the unit compressive strength shall be confirmed by test as an input to the prism strength verification. Units failing to meet specified compressive strength minimums shall be rejected and removed from the site.
Concrete masonry units for load-bearing applications shall comply with ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units. ASTM C90 covers both hollow and solid units, in any weight classification. Load-bearing CMU shall be tested and certified as meeting the minimum net area compressive strength requirements of ASTM C90 before incorporation into the work.
Concrete masonry units for non-load-bearing partitions may comply with ASTM C129, Standard Specification for Nonloadbearing Concrete Masonry Units, where non-load-bearing use is confirmed by the structural engineer. Non-load-bearing units shall not be substituted for load-bearing units in walls where load transfer occurs unless reviewed and approved by the Engineer of Record.
CMU weight classification affects thermal mass, acoustic performance, and handling. Lightweight CMU (less than 105 pcf) uses pumice, expanded shale, or other lightweight aggregates; it is lighter and provides slightly higher thermal resistance but lower acoustic mass than medium or normal weight. Normal weight CMU (125 pcf or greater) uses natural aggregates. The weight classification shall be as required by the structural design and acoustic or thermal requirements of the project.
Lintel units (U-shaped or channel units), bond beam units, pilaster units, and corner units shall be of the same manufacturer, weight class, and color as the field units. Cutting of standard units to form nonstandard shapes is acceptable only where the cut surface will be concealed in the completed work. Saw-cut exposed CMU faces at reveals, edges, and openings shall be ground smooth and present an appearance consistent with the surrounding masonry.
Concrete brick for load-bearing applications shall comply with ASTM C55, Standard Specification for Concrete Brick. Concrete brick may be used as an alternative to clay brick in non-severe weathering environments and where the surface appearance of concrete brick is acceptable to the Architect. Concrete brick shall not be used in locations subject to constant moisture saturation without confirmation that the specified unit grade is appropriate for the exposure.
Clay facing brick shall comply with ASTM C216, Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale). ASTM C216 is the specification for solid clay or shale brick intended to be used as the exposed face of masonry, where appearance quality is required. Grades SW and MW reflect weathering resistance; Types FBS, FBX, and FBA reflect dimensional tolerance and surface appearance.
Grade SW (Severe Weathering) brick shall be used in all exterior applications and wherever brick may be in contact with the ground or subject to water saturation with freezing. Grade MW (Moderate Weathering) brick is only appropriate in regions with a low weathering index and where the brick will not be subjected to repeated freezing while saturated.
ASTM C216 Type FBX provides the tightest dimensional tolerances and most uniform appearance, making it appropriate for exposed interior masonry and high-visibility exterior work. Type FBS covers the majority of standard brick applications. Type FBA allows greater variation in size and texture to achieve a handmade or rustic architectural effect.
Brick shall be delivered to the site in unopened packages when possible. Each unit shall be examined for cracks, chips at arris corners, warping, and color inconsistency before laying. Units with cracks passing through the full face, chips exceeding 1/4 in., or color variation outside the accepted sample range shall be rejected and set aside. The Contractor shall not incorporate rejected units into the work.
Where hollow clay brick is indicated on the contract documents, it shall comply with ASTM C652, Standard Specification for Hollow Brick. ASTM C652 covers hollow clay masonry units with void areas between 25 and 60 percent of the gross cross-sectional area. Hollow brick may be used in veneer and non-reinforced applications; its use in reinforced or grouted applications shall be confirmed with the Engineer of Record.
Where utility grade clay brick not requiring a finished face is indicated — in below-grade applications or where brick will be plastered or coated — it shall comply with ASTM C62, Standard Specification for Building Brick.
Masonry units shall be delivered and stored so that they are protected from wetting, contamination, and damage. Concrete masonry units shall not be wetted before installation; wet CMU shrinks as it dries in the wall, producing horizontal cracking at the bed joints. Packages shall be stored off the ground on level platforms, covered with weatherproof covers that allow air circulation on the sides to prevent condensation.
Clay brick units shall be delivered with a moisture content appropriate to the initial rate of absorption (IRA) of the unit. Brick with an IRA greater than 30 g/min/30 in² shall be wetted before laying so that the IRA at time of laying is in the range of 5 to 25 g/min/30 in², permitting proper mortar bond to develop. Brick with a low IRA does not need prewetting; if prewetted, excessively wet brick can float in the mortar bed and resist proper seating.
Masonry units shall not be stored in direct contact with the ground or in standing water. Units stored outdoors overnight or during rain shall be covered with waterproof sheeting, anchored to prevent wind displacement, but open at the bottom to allow air circulation and drainage. Units damaged by freezing while wet shall be discarded.
Mortar for unit masonry shall comply with ASTM C270, Standard Specification for Mortar for Unit Masonry. ASTM C270 provides four mortar types — M, S, N, and O — and permits specification by either the proportion method or the property method. The property method specifies compressive strength and water retention of the finished mortar; the proportion method specifies the proportions of cementitious materials and aggregate. For most commercial work, the proportion method is simpler and more directly verifiable in the field, but where mortar performance is critical or cementitious materials are non-standard, the property method provides a more direct performance assurance.
Mortar shall not be retempered more than once and shall be used within two hours of initial mixing at temperatures above 80°F, or within 2.5 hours at temperatures of 40 to 80°F. Mortar that has stiffened due to evaporation may be retempered one time by adding water and remixing; mortar that has stiffened due to hydration — judged by the inability to return to working consistency with normal amounts of water — shall be discarded. Mortar that has been standing for more than the allowable time shall be discarded.
The four principal mortar types represent a descending scale of compressive strength: Type M is strongest, followed by Type S, Type N, and Type O. Higher compressive strength in mortar is not always better; a mortar that is significantly stronger than the masonry units it binds can cause units to crack under differential movement, and overly strong mortar reduces the ability of the joint to accommodate minor movement without cracking. The correct mortar type is the one appropriate to the application and to the masonry unit type — not necessarily the strongest.
Type M mortar, with a minimum compressive strength of 2,500 psi at 28 days (property method), is the strongest mortar and provides high resistance to freeze-thaw and to lateral soil pressure. It is appropriate for below-grade masonry in contact with soil, masonry in contact with the ground, and retaining walls where high compressive strength is needed. Type M mortar's high strength can make it brittle in above-grade applications and is not recommended for historic or soft brick because it can cause unit damage.
Type S mortar, with a minimum compressive strength of 1,800 psi at 28 days (property method), provides high bond strength and tensile strength and is the most versatile type for reinforced masonry above grade and for exterior masonry subject to severe weathering, wind pressure, and lateral loads. Type S is the most commonly specified mortar for structural masonry in commercial construction.
Type N mortar, with a minimum compressive strength of 750 psi at 28 days (property method), provides good workability and bond for above-grade exterior masonry not subject to significant lateral loads, and for interior non-load-bearing masonry. Type N is the appropriate choice for soft or historic brick, where a mortar that is weaker than the unit prevents unit damage, and for above-grade veneer not subject to high lateral forces.
Type O mortar, with a minimum compressive strength of 350 psi at 28 days (property method), is a low-strength mortar for interior non-load-bearing and above-grade applications in sheltered locations where there is no freeze-thaw exposure. Type O shall not be used in exterior or freeze-thaw applications.
ASTM C270 recognizes several cementitious material combinations: portland cement-lime, masonry cement, mortar cement, and combinations thereof. Portland cement-lime mortars are made from portland cement conforming to ASTM C150, hydrated lime conforming to ASTM C207 Type S, and aggregate conforming to ASTM C144. Masonry cement mortars substitute a pre-blended, proprietary masonry cement complying with ASTM C91 for the portland cement-lime combination. Mortar cement, complying with ASTM C1329, is similar to masonry cement but has specified minimum flexural bond strength requirements.
Portland cement-lime mortar provides the highest and most predictable bond strength and the greatest control over mortar properties, and is recommended for structural and exterior applications. Masonry cement mortar is convenient and consistent from bag to bag, but its air content and admixture composition is not fully disclosed by all manufacturers, which can complicate troubleshooting. Mortar cement is intermediate between the two and is a good choice where a factory-proportioned system is preferred but bond strength requirements are specified.
Aggregate for mortar shall comply with ASTM C144. Aggregate gradation and cleanliness significantly affect mortar workability and bond. Aggregate shall be clean, free of organic matter, and conforming to the gradation requirements of ASTM C144. Concrete sand — which meets ASTM C33 but not ASTM C144 — shall not be substituted for masonry mortar aggregate without testing to confirm compliance with C144.
Admixtures in mortar shall be limited to those specifically listed in ASTM C270 or approved in writing by the Engineer. Set accelerators, set retarders, and workability agents are acceptable where required for cold or hot weather construction; antifreeze compounds that reduce the freezing point of the mix water are not permitted because they reduce mortar strength and durability. Air-entraining agents are not permitted in mortar for reinforced masonry unless specifically approved by the Engineer, because they reduce bond strength. Calcium chloride or admixtures containing calcium chloride shall not be used in mortar in any application; chloride ions accelerate corrosion of joint reinforcement and embedded metal ties.
Grout for masonry shall comply with ASTM C476, Standard Specification for Grout for Masonry. Grout fills the cells of CMU or the collar joint of brick masonry, embedding vertical reinforcement and bonding it to the masonry assembly. Properly placed grout transforms a hollow masonry shell into a composite structural element.
ASTM C476 provides two classifications — fine grout and coarse grout — and two placing methods — conventional grout (requiring consolidation by puddling or mechanical vibration) and self-consolidating grout (which flows into place without mechanical vibration due to its high fluidity). Self-consolidating grout must still be contained within the masonry during placement and must achieve the same strength and bond requirements as conventional grout.
The maximum aggregate size for fine grout (3/8 in.) and for coarse grout (1/2 in.) is a maximum, not a minimum. Fine grout shall be used wherever the clear dimension of the grout space — the clear distance between the masonry unit face and the reinforcing bar, or the narrowest clear dimension in the grout pour — is less than 2 in. If the clear dimension is 2 in. or greater in both directions, coarse grout may be used. The use of oversized aggregate in a restricted cell or collar joint is one of the most common causes of grout segregation and incomplete cell fill.
Grout slump at point of delivery to the wall shall be between 8 and 11 inches for conventional grout, as required by TMS 602 Article 3.5 and ASTM C476. High slump is intentional and necessary in grout — it is not a quality defect as it would be in structural concrete — because grout must flow into and completely fill the internal cavities of the masonry. Water will be absorbed by the surrounding masonry units, and the apparent water-to-cement ratio of the hardened grout will be substantially lower than the mixing ratio. Grout shall not be retempered after the initial placement if consolidation is complete.
Grout pour height and lift height are controlled to prevent blowout of the mortar bed joints under the hydrostatic pressure of wet grout and to ensure that the grout can be properly consolidated. TMS 602 Article 3.5D establishes maximum grout pour heights based on grout space dimensions and the grouting method.
Conventional grout shall be consolidated immediately after placement by mechanical vibration or by rodding (puddling), to a depth of no more than 18 in. The vibrator shall be inserted and withdrawn slowly to avoid air pockets and shall not be used to move grout horizontally. Each lift in a multi-lift pour shall be reconsolidated after the grout has settled and before it has taken its initial set, typically 15 to 30 minutes after placement. The intent of reconsolidation is to close the settlement void that forms as bleed water is absorbed into the masonry and to re-establish intimate contact between the grout and the reinforcement.
Joint reinforcement is prefabricated welded wire assemblies embedded in the mortar bed joints to control cracking, distribute stress, and in some configurations provide horizontal shear transfer. Joint reinforcement shall comply with ASTM A951, Standard Specification for Steel Wire for Masonry Joint Reinforcement, and shall be of the truss or ladder configuration as indicated on the contract documents.
Ladder-type joint reinforcement consists of two longitudinal wires connected by straight cross wires perpendicular to the wall face; truss-type uses diagonal cross wires. Ladder-type is preferred for walls with open vertical cells because the straight cross wires do not obstruct grout flow from cell to cell; truss-type has greater shear stiffness in the horizontal plane. For partially grouted or solidly grouted CMU walls with joint reinforcement, ladder-type is the standard specification unless the structural engineer specifically requires truss-type.
Joint reinforcement spacing in the wall height governs the crack control performance. Spacing at 16 in. o.c. (every other course in 8-in. CMU) is the standard for crack control in CMU backup walls and non-structural CMU partitions. Closer spacing is required by the structural engineer for shear walls or where the design calls for distributed horizontal reinforcement.
Corrosion protection of joint reinforcement is critical because joint reinforcement is embedded in a thin mortar bed that may not provide the same alkalinity protection as dense concrete. For exterior walls and interior walls exposed to a mean relative humidity greater than 75 percent, joint reinforcement shall be hot-dip galvanized after fabrication in accordance with ASTM A153. Mill-galvanized (in-process) coating is not equivalent and shall not be substituted where hot-dip galvanized is required. For conditions of high chloride exposure — coastal environments, de-icing salt exposure — stainless steel joint reinforcement conforming to ASTM A580 shall be used.
Joint reinforcement shall be lapped a minimum of 6 in. at splices, with laps located at least 8 in. from corners, intersections, and changes in wall direction. At corners, proprietary corner and tee units of matching wire diameter shall be used; field-bent laps at corners shall not be used as a substitute for fabricated corners because field bending kinks the wire and reduces section properties.
Deformed reinforcing bars for vertical reinforcement in masonry cells and pilasters shall conform to ASTM A615, Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, Grade 60, or ASTM A706, Low-Alloy Steel Deformed Bars, Grade 60. Where welding of reinforcing bars is required or anticipated, ASTM A706 bars shall be specified because their chemistry is controlled for weldability; ASTM A615 bars require supplemental chemical analysis before welding.
Masonry cover requirements for reinforcing bars shall comply with TMS 602 Article 2.4. Bars in cells of CMU shall have a minimum clear distance between the bar and the masonry unit face shell of 1/4 in. for fine grout and 1/2 in. for coarse grout. The bar diameter shall not exceed one-eighth of the nominal wall thickness or one-fourth of the least clear dimension of the cell into which it is placed, per IBC Chapter 21. Bars in the same cell shall be separated by a clear distance of not less than the nominal bar diameter and not less than 1 in.
Reinforcement shall be positioned in the center of the cell, or as shown on the structural drawings, and held in place during grouting by bar positioners or by securing to joint reinforcement at intervals not greater than 192 bar diameters. Bars shall not be moved from the specified position during grouting. Where bars are displaced by grouting pressure, the displaced portion shall be excavated and the bar repositioned before the grout sets.
Lap splice lengths and hook dimensions shall be as indicated on the structural drawings and shall comply with TMS 402 Chapter 8. Lap splice lengths for deformed bars in grouted masonry are typically longer than equivalent concrete lap splices because the confinement provided by masonry grout may be less than concrete. The Contractor shall not reduce lap lengths from those shown on the structural drawings without written authorization from the structural engineer.
Wall ties connect a masonry veneer to a backup wall — whether CMU, stud framing, concrete, or structural steel — and transfer wind pressure and seismic loads from the veneer to the structure while allowing differential vertical movement between the veneer and backup. Anchors connect a masonry wythes to a structural frame member.
Wall ties shall be fabricated from steel sheet conforming to ASTM A1008, from steel wire, or from stainless steel as required by the corrosion exposure. Adjustable two-piece ties, with a plate or channel anchor embedded in the backup and a wire eye or slot tie engaging the masonry veneer, provide vertical adjustment to accommodate differential movement and construction tolerances. Fixed ties shall only be used where adjustment is not required and where the differential movement between the backup and the veneer is negligible.
Wall ties for masonry veneer shall be spaced at a maximum of one tie per 2.67 sq ft of wall area, with maximum horizontal spacing of 36 in. and maximum vertical spacing of 24 in. In Seismic Design Categories C through F, or where indicated on the structural drawings, tie spacing shall be reduced and tie type shall be as required by TMS 402. Wall tie placement shall be adjusted so that each tie is fully embedded in the mortar bed joint with a minimum of 1-1/2 in. of mortar embedment on each side. Ties shall not bridge a cavity where the cavity is a designed drainage space.
Through-wall flashing at the base of exterior masonry wythes, above shelf angles, above lintels, at window and door heads, and at any horizontal interruption of the cavity is the most important single element in preventing moisture intrusion into the building. Water that penetrates through mortar joints, unit face shells, or cracks — as it will on any exterior masonry wall over time — must be intercepted at these points and directed out through the weep system. Omitted, improperly lapped, or improperly turned flashing is the single most common cause of masonry water infiltration and one of the most common RFI generators on masonry projects.
Through-wall flashing shall be a fully continuous sheet-type flashing, turned up into a reglet or turned back and sealed, and turned down to the face of the masonry to form a drip edge or carried to the outside face. The flashing shall extend continuously across the full length of the condition it protects, lapped a minimum of 6 in. at splices, with end dams at each end to contain water within the drainage plane.
The flashing shall be set in mortar or adhered to the backup so that it is fully supported. Flashing that hangs unsupported across the cavity will sag and pond water rather than drain it. Where the cavity contains insulation, the flashing shall be continuous across the insulation and supported at the masonry face by a mortar bed. The leading edge of the flashing shall project at least 1/4 in. beyond the face of the masonry to form a visible drip.
Mortar droppings in the cavity are the most common cause of blocked flashing and blocked weeps. Mortar collection devices — plastic or foam mesh rope installed in the cavity at the flashing level — shall be used to catch mortar droppings before they reach the flashing. After the masonry above is set and before the weep holes are closed with temporary protection, the mortar collection device shall be removed or left in place as the product manufacturer directs. Metal lath or hardware cloth used as a mortar collection device shall be of compatible metal (galvanized or stainless, never plain steel) to avoid rust staining.
Weep holes provide the drainage outlet for water intercepted by through-wall flashing. Weeps shall be located at the mortar bed joint immediately above the flashing at head joint locations. The maximum spacing of weep holes shall be 24 in. o.c., with open head joint weeps having a minimum clear opening of 3/4 in. wide and full-joint height. Screens or plastic weep inserts shall be set in the joint and shall not block the drainage opening; louvered plastic inserts shall be confirmed to be open to drainage and not merely ornamental.
Weep holes shall be kept free and clear at all times during and after construction. Paint, sealants, and cleaning solutions shall not be applied across weep openings. At final inspection, the Contractor shall verify that every weep opening is unobstructed by inserting a straight probe into each opening to confirm a clear path to the cavity.
Concrete masonry shrinks as it cures and as the moisture content of the unit changes seasonally. Without control joints, this shrinkage produces vertical cracks that are random in location and uncontrolled in severity. Control joints are intentional vertical discontinuities that concentrate movement at planned locations, keeping the field masonry crack-free between joints.
Control joints in CMU walls shall be provided at vertical locations shown on the structural and architectural drawings. Where joint locations are not fully detailed, the Contractor shall install control joints at the following maximum intervals, unless directed otherwise by the Engineer of Record. In exterior unreinforced or lightly reinforced CMU walls, control joint spacing shall not exceed 25 feet. At returns, openings, and changes in wall height, control joints shall be located within 4 feet of the discontinuity. At intersecting wall conditions, control joint placement shall be coordinated with the structural engineer to preserve load paths.
Control joint vertical sealant and backer rod shall be installed after masonry is complete and cured. The joint cavity shall be maintained through the full thickness of the wall. Sealant shall be a flexible, paintable polyurethane or silicone product, tooled flush with the face of the masonry. The backer rod shall be closed-cell polyethylene foam sized to provide approximately 25 percent compression when installed. The control joint sealant system shall comply with movement joint requirements of this section.
Clay brick undergoes irreversible moisture expansion after firing — the brick grows slightly in size over time as it absorbs atmospheric moisture. This expansion is permanent and cumulative and will cause cracking or delamination of the masonry if it is not accommodated. Expansion joints in clay brick veneer allow the masonry to expand without developing compressive stress that would otherwise bow or crack the wall.
Expansion joints in clay brick veneer shall be provided at vertical locations shown on the drawings. In unreinforced clay brick veneer on multi-story buildings, expansion joint spacing shall generally not exceed 25 feet horizontally and shall be provided at every floor line where the veneer bears on a shelf angle. Expansion joints shall also be provided at returns, at changes in wall direction, and at major re-entrant corners.
Unlike control joints in CMU — which accommodate shrinkage and must be filled with a compressible sealant — expansion joints in brick must remain free of all rigid material so that the expanding brick has room to move. No mortar, grout, or hardened filler shall be placed in a brick expansion joint. The joint shall be filled with a closed-cell foam backer rod and a flexible elastomeric sealant, or with a premolded compressible filler, tooled flush with the brick face on both sides.
Movement joint sealant shall be a single-component or two-component polyurethane or silicone sealant, selected for compatibility with the adjacent masonry and with any primers or flashing membranes present. Polyurethane sealant is preferred for painted or coatable surfaces. Silicone sealant provides superior UV and temperature resistance and is preferred for unpainted masonry in direct sun exposure.
Backer rod shall be closed-cell polyethylene foam rod of a diameter approximately 25 percent larger than the joint width, so that it is compressed slightly when installed and positively contacts both sides of the joint. The backer rod limits sealant depth to approximately 50 percent of joint width and prevents three-sided adhesion, which would prevent the sealant from performing its two-sided elongation function.
Cold weather masonry construction requires active measures to protect freshly placed mortar and grout from freezing before adequate strength is achieved. Mortar that freezes before reaching a compressive strength of approximately 500 psi will suffer permanent strength loss and bond failure due to ice crystal formation in the mortar matrix. Cold weather procedures shall be implemented whenever the ambient temperature is below 40°F or is forecast to drop below 40°F within 24 hours.
The following temperature thresholds define required protection levels in accordance with TMS 602 Article 1.8C and accepted industry practice.
When the ambient temperature is between 40°F and 32°F, mortar and grout shall be heated to provide a temperature between 40°F and 120°F at the time of placement. All materials, mixing water, and mixing equipment shall be protected from freezing. Completed masonry shall be covered with weather-resistant membrane for 24 hours after construction.
When the ambient temperature is between 32°F and 25°F, mortar and grout materials and mixing water shall be heated as above. Masonry units shall be heated to at least 40°F before laying. The top of completed masonry shall be covered with weather-resistant membrane for 48 hours after construction, and all masonry surfaces within the heated enclosure shall be protected.
When the ambient temperature is between 25°F and 20°F, masonry shall be constructed within a heated enclosure that maintains a temperature of at least 40°F throughout the masonry and for the 24-hour period after construction. Completed masonry shall be covered with insulating blankets for a minimum of 24 hours after construction in addition to the heated enclosure.
When the ambient temperature is below 20°F, masonry work shall not be performed unless the Contractor provides a heated enclosure maintaining the masonry and its immediate environment above 40°F for the duration of construction and for at least 24 hours after completion.
Heating of masonry materials shall use dry heat sources. Steam or wet heat in a poorly ventilated enclosure raises humidity and causes condensation on masonry units, which reduces mortar bond. Carbon monoxide from combustion heaters can be a safety hazard; heaters shall be vented to the outside or the enclosure shall be monitored for CO levels. Antifreeze admixtures shall not be used in masonry mortar or grout; they reduce strength and are prohibited by TMS 602.
Hot weather accelerates the evaporation of water from mortar, reduces mortar board life, and reduces the amount of water available for cement hydration. Rapid evaporation before mortar sets reduces bond strength and produces weak, friable mortar joints that may later erode. Hot weather procedures shall be implemented when the ambient temperature exceeds 90°F, when the temperature is above 80°F with wind velocities exceeding 8 mph, or when direct sun heats the masonry surface significantly above the ambient temperature.
During hot weather, mixing water shall be cooled or iced, mixing equipment shall be shaded, and mortar board life shall be reduced to no more than one hour from time of mixing. Masonry units shall be shaded from direct sun before laying where possible. Newly completed masonry shall be protected from direct sun and wind with opaque covering for at least 24 hours in extreme hot or dry conditions. Masonry shall not be constructed when temperatures exceed 115°F or when temperatures exceed 105°F with wind velocity greater than 8 mph, unless approved hot weather procedures are implemented.
The service environment determines the appropriate unit grade, mortar type, and protection level for the masonry assembly. At-grade and below-grade applications in contact with soil, and all-weather exterior applications, require the highest durability — Grade SW brick, ASTM C90 CMU, and Type S or M mortar. Above-grade exterior protected applications allow Grade MW brick, standard ASTM C90 units, and Type N mortar. Interior protected applications not subject to moisture have the widest range of acceptable materials.
Before beginning masonry installation, the Contractor shall establish horizontal and vertical control lines and confirm that all anchor bolts, embedded plates, and other items set by other trades are in the correct location and within the tolerances permitted by this specification. Masonry shall not be placed on or around embedded items that are out of tolerance, because the masonry will then be out of tolerance; discrepancies shall be reported to the Architect and Engineer before they are concealed.
Coursing shall be laid out on a story pole or modular layout rule for each wall before beginning, to confirm that the course height at each window and door opening, at lintels, at shelf angles, and at the top of wall lands at a full course without excessive cutting. Masonry units shall be laid in running bond unless otherwise indicated on the contract documents. Running bond provides the maximum interlocking of units and the best resistance to vertical crack propagation. Stack bond — units stacked directly above one another in a grid — is architecturally distinctive but provides no interlocking and shall only be used where specifically shown on the drawings and where horizontal joint reinforcement compensates for the lack of mechanical interlock.
Mortar joints shall be a nominal 3/8 in. in thickness. The permitted range of joint thickness for standard coursing is 1/4 in. to 1/2 in. for fully bedded joints and bond beam joints. The first course bed joint on a concrete slab or footing may be 1/4 to 3/4 in. thick in ungrouted construction and up to 1-1/4 in. thick in fully grouted construction to accommodate levelness variation in the base surface.
Face-shell bedding — mortar applied to the outer face shells of CMU only, leaving the interior web area unbeaded — is the standard for hollow CMU construction and is specifically permitted by TMS 602. Full mortar bedding — mortar applied to the entire top surface of the unit, including webs — is required at the first course, at bond beams, at top-of-wall courses, and at all horizontal surfaces that will receive concentrated loads.
Head joints shall be filled solidly with mortar from the face of the unit to a depth of at least 1 in. for face-shell-bedded CMU, and for the full thickness of the joint for solid or fully grouted construction. Furrowing or spreading a thin slice of mortar down the center of the bed joint — sometimes called "buttering" or "slushing" — is not permitted; the mortar bed shall be of full depth and shall fill the bed joint from face to face. Mortar shall not be spread more than 48 in. ahead of the units being laid so that it does not dry or stiffen before the unit is embedded.
Mortar joints shall be tooled to a concave profile unless otherwise specified. Tooling shall be done when the mortar has reached thumb-print hardness — neither too fresh (tooling will pull mortar out of the joint) nor too hard (tooling will crack the mortar along the edges). Concave tooling densifies the mortar at the joint face and improves weathering performance by creating a slightly recessed surface that sheds water. Struck, raked, or flush joints are permissible where specified but provide less weather resistance than concave joints.
All masonry units shall be laid plumb, level, and true to line. Units shall be set firmly into the mortar bed with a solid full-bearing contact. Tapping units into place shall be done with the masonry hammer handle, never with the metal head, and never after the mortar has begun to set. Units shall not be shifted or realigned after the mortar has begun to set; mortar that has begun initial set and is then disturbed breaks the bond between the mortar and the unit, producing a weak joint that may later leak or fail in tension. Units that have been set and then disturbed shall be removed, the joint cleaned, and fresh mortar applied before the unit is reset.
Masonry shall be built to a line, established by a mason's line stretched taut between leads. Leads at corners and intersections shall be built up first and checked for plumb and level before the body of the wall is laid between them. The leads shall be built level and plumb in all directions; a lead that is out of plumb introduces error into every course that follows it.
Cells to be grouted shall be kept free of mortar droppings and debris throughout the work. Before grouting, the Contractor shall perform a visual inspection of each lift by looking down the cells from the top. Cells shall be clean and free of mortar bridges, loose mortar droppings, and foreign material that would prevent complete cell fill.
Lintels shall be as indicated on the structural drawings. Prefabricated steel lintels shall be hot-dip galvanized for exterior applications. Reinforced masonry lintels (lintel courses of bond beam CMU filled with reinforcing bars and grout) shall be constructed and grouted before the masonry above is built. The support of the masonry above the lintel shall be maintained until the lintel has achieved sufficient strength; shoring requirements shall be as directed by the structural engineer.
Anchor bolts, straps, plates, and other embedded items shall be set and grouted into the masonry as indicated on the structural drawings. Embedded items shall be positioned before grouting and shall not be moved after the grout has begun to set. Anchor bolts shall be set plumb in grout-filled cells, with the specified embedment length and projection. Bent-bar anchors hooked around joint reinforcement or around a reinforcing bar are more reliable in tension than unbonded straight bolts and shall be used where indicated.
Steel shelf angles supporting masonry veneers or facing courses shall be continuously through-wall flashed above, with the flashing turned up behind the shelf angle and turned down to form a drip. The horizontal leg of the shelf angle shall receive a continuous bed of mortar under the first masonry course. Expansion joints shall be located directly below each shelf angle so that the masonry can expand without loading the shelf angle in compression. Where the structural engineer has identified shelf angles as carrying significant loads, installation shall be coordinated with the structural steel subcontractor and verified before masonry above is placed.
Where specified compressive strength of masonry (f'm) is indicated on the contract documents, verification of f'm shall be by masonry prism testing in accordance with ASTM C1314, Standard Test Method for Compressive Strength of Masonry Prisms. Prism testing is the most direct method of verifying the combined performance of the unit, mortar, and grouting system as an assembly.
Prisms shall be constructed by the Contractor in the presence of the Special Inspector from the same units, mortar, and grout used in the production work, using the same laying procedure. Prisms shall consist of a minimum of three masonry units in height. Prisms shall be transported to the laboratory without damage and tested at 28 days, unless the specifying engineer approves earlier testing with an age factor. At least three prisms per masonry wythe per set shall be tested, with the average strength representing the lot.
If the prism test result is below f'm, the Contractor shall notify the structural engineer immediately. Work shall not proceed on the affected masonry area until the structural engineer has reviewed the test result and directed corrective action. Corrective action may include additional testing, coring of in-place masonry for core testing, or analysis by the structural engineer to determine whether the lower strength is structurally acceptable.
Mortar sampling and testing shall be performed in accordance with ASTM C780, Standard Test Method for Preconstruction and Construction Evaluation of Mortars. Preconstruction mortar tests using the mix proportions and materials proposed for the project shall be used to establish the baseline properties. During construction, periodic samples shall be taken from the mortar board and tested for compressive strength and water retention.
Mortar samples shall be taken from a representative location on the mortar board after the mortar has been spread but before units are laid. Samples shall be taken at the rate of at least one per each 5,000 sq ft of masonry wall area, or as directed by the Special Inspector. Sample results are used as a consistency check and for quality documentation; mortar sampled from the mortar board does not represent the hardened mortar in the joint because the mortar in the joint loses water to the units and achieves higher strength.
Grout samples shall be taken in accordance with ASTM C1019, Standard Test Method for Sampling and Testing Grout, from the grout at the point of delivery into the wall. Grout shall not be sampled from the transit mixer drum because mixing continues during transit; the delivered sample represents the grout actually entering the wall. Test frequency shall be at least one set of two specimens per grout pour, or as directed by the special inspection program.
Grout slump shall be measured and recorded for every grout pour to confirm that the slump is within the 8 to 11 inch required range. Slump tests shall be performed at the grout truck discharge, immediately before placement, using a standard slump cone per ASTM C143. Grout with slump outside the range shall be rejected; it shall not be adjusted by adding water or aggregate in the field without recalculating the mix design.
The Special Inspector shall be present during all grouting operations for structural masonry in Inspection Level B and Level C programs. The Special Inspector shall observe: the slump of each grout delivery; that cells to be grouted are clean; that reinforcement is properly positioned; that lift heights and consolidation procedures comply with the approved grouting procedure; and that reconsolidation is performed within the specified time window.
Masonry cleaning shall be performed after the masonry is complete and has cured for a minimum of seven days, unless directed otherwise by the material manufacturer. Cleaning shall be completed before sealants, coatings, or adjacent finished materials are installed.
Before cleaning, all mortar droppings and loose mortar smears shall be removed from the masonry face using a wooden paddle, a chisel, or a wood block. Steel tools that could damage the masonry face or leave metal fragments that later rust shall not be used on the masonry face. Cured mortar protrusions shall be carefully chipped away by hand before any liquid cleaning agent is applied. Mechanical wire brushing shall not be performed on clay brick because it can abrade the fired face of the unit, permanently changing its texture and color.
All masonry surfaces to be cleaned shall be thoroughly pre-saturated with clean water from the top down, using a garden hose or low-pressure spray. Pre-saturation is essential because it prevents the masonry from absorbing the cleaning solution and prevents cleaned mortar particles from being drawn into the pores of the unit. Unsaturated masonry absorbs the cleaning solution along with dissolved mortar products, resulting in permanent staining.
Proprietary masonry cleaners with buffered acid or non-acid cleaning agents are the preferred choice for most masonry cleaning. These products are formulated to clean effectively without etching or staining the masonry face, and their dwell time and rinsing requirements are established by the manufacturer. The Contractor shall submit the proposed cleaning product and confirm its suitability for the specific masonry unit type before beginning cleaning.
High-concentration acids — including straight muriatic acid — shall not be used for cleaning masonry. Strong acid etches the surface of clay brick and CMU, permanently changes the surface texture, can bleach out fired colors, and dissolves calcium compounds from CMU that then re-deposit as white haze. Where dilute acid cleaning is approved by the Architect and confirmed as suitable by the masonry unit manufacturer for dense, hard-burned clay brick, dilution shall be per the manufacturer's specific recommendation and shall be no stronger than necessary.
After applying the cleaning solution and allowing the manufacturer's specified dwell time, the wall shall be rinsed thoroughly from the top down with a high-pressure water rinse of at least 400 psi and 4 to 6 gallons per minute. Rinsing must remove all cleaning solution and dissolved materials from the wall face and from the wall immediately below the cleaned area. Inadequate rinsing results in streaking and re-deposition of dissolved salts, which is difficult or impossible to correct after it has dried.
Areas adjacent to the masonry being cleaned — windows, doors, sealant joints, adjacent cladding, and paving — shall be masked or protected from the cleaning solution and rinse water. Sealants and painted surfaces are particularly vulnerable to acid attack and shall be masked before cleaning.
Mortar haze shall be cleaned within 10 days of laying the masonry. After one month, mortar smears and droppings become progressively more difficult to remove and may require mechanical intervention that risks damaging the masonry face. Prompt cleaning is both easier and more likely to achieve a clean result.
Efflorescence — the white, powdery salt deposits that can appear on masonry faces — is caused by soluble salts within the masonry or its mortar being carried to the surface by water migration and then crystallizing as the water evaporates. Efflorescence does not indicate a structural problem, but it is visually objectionable and its presence indicates that water is migrating through the masonry, which should be investigated as a potential precursor to freeze-thaw damage.
Where efflorescence is present on completed masonry, it shall be dry-brushed away with a stiff fiber brush when dry. Rewetting efflorescence drives the salt back into the masonry. Where efflorescence is heavy or persistent, the source of water migration shall be identified and corrected; simply cleaning the face without stopping the water source will result in recurrence.
Masonry unit dimensional variation — the difference between the specified nominal dimension and the as-manufactured dimension — shall conform to the applicable ASTM product standard. The acceptable variation of individual CMU dimensions per ASTM C90 is ± 1/8 in. on length and height. The acceptable variation for clay facing brick per ASTM C216 Type FBX is ± 1/16 in. on length and ± 1/32 in. on height; Type FBS is ± 1/8 in. on length and ± 1/8 in. on height. Units outside the specified dimensional tolerance shall be rejected.
Construction tolerances for completed masonry work shall conform to TMS 602 Article 3.3 and shall be verified by the Special Inspector and the Architect. The following tolerances shall apply.
Variation from plumb in the planes and lines of walls, columns, and arises shall not exceed ± 1/4 in. in 10 ft, ± 3/8 in. in 20 ft, and ± 1/2 in. maximum in any height.
Variation from level in bed joints, top of wall, and horizontal coursing shall not exceed ± 1/4 in. in 10 ft and ± 1/2 in. maximum in any length.
Variation in location of elements in plan from the established position shown on the contract documents shall not exceed ± 1/2 in. for any element.
Variation in mortar bed joint thickness from the specified 3/8 in. nominal shall not exceed ± 1/8 in. per joint, and the total variation in cumulative coursing heights shall not exceed ± 3/8 in. in 10 ft.
Variation in head joint thickness from the specified 3/8 in. nominal shall not exceed ± 1/8 in.
Variation in wall thickness from the specified nominal shall not exceed -1/4 in. or +3/8 in.
Variation in the location of cells, bond beams, and reinforcing bars from the location shown on the structural drawings shall not exceed ± 1 in. vertically and ± 2 in. horizontally, except that reinforcing bars required by structural design shall not be displaced from the design location by more than 1/2 in. without review by the Engineer of Record.
The Contractor shall monitor dimensional compliance continuously during construction. Leads shall be checked for plumb and level before each course is laid. At the completion of each lift or each floor level, the Contractor shall survey the as-built wall face for plumb and check the horizontal position against the control lines.
The Architect and Special Inspector shall verify tolerances at regular intervals and at substantial completion. Masonry that exceeds the permitted tolerances and that has been brought to the attention of the Contractor shall be corrected before subsequent work conceals it. Correction methods — including demolition and rebuilding — shall be proposed by the Contractor and reviewed by the Architect and Engineer before correction work begins.
The Contractor shall warrant all masonry construction against defects in materials and workmanship for the project standard warranty period, beginning at substantial completion.
The Contractor's warranty shall specifically cover workmanship deficiencies including: mortar joint failures, delamination of masonry units, water infiltration attributable to improperly installed flashing or weeps, blocked or missing weep holes, and failure to achieve the specified compressive strength f'm as demonstrated by prism test results. The warranty does not cover damage caused by Owner modification, extraordinary weather events beyond the project's design basis, or movement attributable to foundation settlement or structural frame deflection outside the tolerances provided to the Contractor.
Where masonry prism test results fell below f'm and the structural engineer accepted the masonry at a reduced strength with appropriate design modifications, the Contractor shall document the accepted deviation and include it in the closeout submittal. The warranty for such areas is limited to workmanship and installation quality and does not independently warrant structural performance; structural performance at reduced f'm is an engineering determination made by the Engineer of Record.