1 Scope

NOTE This specification covers the materials, joint preparation, and application of cold liquid-applied joint sealants and their associated backings and primers used to seal joints in exterior and interior building construction. (1.1)

1.2 Work Included

NOTE The work includes weatherproofing sealants at exterior vertical and horizontal joints, sealants at expansion and control joints, sealants at the perimeter of openings, interior acoustical and general-purpose sealants, and sealants in horizontal traffic-bearing joints, together with the backer rods, bond-breaker tapes, primers, and cleaning agents that make up each completed sealed joint. (1.2.1)

1.2.2 All work shall comply with ASTM C1193, the standard guide for the use of joint sealants.

1.2.3 Sealants shall conform to ASTM C920, ASTM C834, or ASTM C1311 as applicable to the chemistry and application.

1.3 The Sealed Joint as an Engineered System

NOTE A sealant joint is not merely a bead of material; it is an engineered system consisting of a substrate, a primer where required, a backing that establishes the sealant's shape, a bond-breaker that controls where the sealant adheres, and the sealant itself. (1.3.1)

NOTE The performance of a sealant joint depends far more on joint design and installation than on the sealant chemistry alone. (1.3.2)

NOTE A premium sealant installed in a joint that is too narrow, filled too deeply, or allowed to bond to three surfaces will fail prematurely, while a modest sealant in a correctly proportioned two-sided joint can last decades. (1.3.3)

1.3.4 The requirements of this standard for joint width, depth, backing, bond-breaking, and surface preparation carry the same weight as the requirements for the sealant material.

1.4 Boundary of Work and Exclusions

NOTE The boundary of work under this standard is the field-applied sealant and its backing and primer in the joints scheduled under it. (1.4.1)

1.4.2 Fire-rated joint systems and firestopping at penetrations are excluded and are covered by FirestoppingFirestoppingResolves to the current edition.sync/firestopping.

NOTE Fire-rated joint systems are tested and listed as assemblies for a fire-resistance rating and use materials and configurations that this standard does not govern. (1.4.3)

1.4.4 Structural and weatherseal silicone within a glazed curtain wall or storefront is excluded and is covered by Glazed Curtain WallsGlazed Curtain WallsResolves to the current edition.sync/glazed-curtain-walls.

1.4.5 The continuous air- and water-resistive barrier and its transition membranes are covered by Air BarriersAir BarriersResolves to the current edition.sync/air-barriers.

NOTE Sealants under this standard interface with the air- and water-resistive barrier but do not replace it. (1.4.6)

2 Referenced Standards

2.1 Materials and installation shall comply with the latest adopted editions of the following standards.

Standard	Title
ASTM C920	Standard Specification for Elastomeric Joint Sealants
ASTM C834	Standard Specification for Latex Sealants
ASTM C1311	Standard Specification for Solvent Release Sealants
ASTM C1193	Standard Guide for Use of Joint Sealants
ASTM C719	Adhesion and Cohesion of Elastomeric Joint Sealants Under Cyclic Movement (Hockman Cycle)
ASTM C794	Adhesion-in-Peel of Elastomeric Joint Sealants
ASTM C661	Indentation Hardness of Elastomeric-Type Sealants by Means of a Durometer
ASTM C1248	Staining of Porous Substrate by Joint Sealants
ASTM C1247	Durability of Sealants Exposed to Continuous Immersion in Liquids
ASTM C1330	Cylindrical Sealant Backing for Use with Cold Liquid-Applied Sealants
ASTM C1521	Evaluating Adhesion of Installed Weatherproofing Sealant Joints
ASTM D1056	Flexible Cellular Materials — Sponge or Expanded Rubber
AAMA 800	Voluntary Specifications and Test Methods for Sealants
AAMA 850	Fenestration Sealants Guide Manual

2.2 Conflicts Between Requirements

2.2.1 Where the contract documents, the adopted building code, the sealant manufacturer's published instructions, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

2.2.2 The sealant manufacturer's written recommendations for substrate, primer, joint configuration, and application conditions are mandatory for that manufacturer's product and shall be followed.

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for the Engineer's review before procurement and application:

Product data for each sealant, stating the ASTM C920, C834, or C1311 designation and, for C920 sealants, the full Type, Grade, Class, and Use classification, together with the chemistry, cure type, movement capability, durometer hardness (ASTM C661), and service temperature range
Product data for each sealant backing, stating the ASTM C1330 type (open-cell, closed-cell, or bi-cellular) or ASTM D1056 designation, the diameter range, and confirmation that it is compatible with the sealant
Product data for each primer and for the cleaning solvents and methods proposed for each substrate
A joint-sealant schedule cross-referencing each joint location and substrate pairing to the specific sealant, primer, backing, and bond-breaker proposed, with the C920 classification for each
Manufacturer's sealant-substrate compatibility and adhesion test results for each project substrate, primer, and sealant combination, or a written request for the Contractor to submit substrate samples to the manufacturer for testing
Color selection samples for each exposed sealant
Manufacturer's written application instructions, including application temperature and humidity limits, joint-width range, primer requirements by substrate, and tooling and cure requirements

Action Submittals Requiredcheckbox

☑ Sealant product data with ASTM C920/C834/C1311 classification

☐ Sealant backing product data (ASTM C1330 / D1056)

☐ Primer and cleaner product data by substrate

☐ Joint-sealant schedule by location and substrate

☐ Manufacturer compatibility and adhesion test results

☐ Color selection samples

☐ Manufacturer written application instructions

3.1.2 Submittals shall be coordinated so that every sealant, primer, and backing proposed for a given joint is mutually compatible and compatible with the adjoining substrates and with any adjacent construction (sheet flashing, glazing seals, air barrier) that the sealant will contact.

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following informational submittals:

Manufacturer's product test reports demonstrating compliance with the specified ASTM C920 Class (movement capability) per ASTM C719, and staining results per ASTM C1248 where the sealant contacts porous stone
Qualification data for the installing firm and applicators
Preconstruction and field adhesion test reports as required under Quality Assurance and Field Quality Control
Sample warranties (the manufacturer's materials warranty and, where required, the special weatherproofing warranty)

Informational Submittals Requiredcheckbox

☑ Manufacturer product test reports (ASTM C920 Class per C719; C1248 staining for porous stone)

☐ Qualification data for installing firm and applicators

☐ Preconstruction and field adhesion test reports

☐ Sample warranties (materials and special weatherproofing)

4 Quality Assurance

4.1 Installer Qualifications

4.1.1 Sealant work shall be performed by a firm experienced in the application of the specified sealant types.

4.1.2 Sealant work shall be performed by a firm approved by the sealant manufacturer where the manufacturer maintains an applicator approval program, particularly where a special weatherproofing warranty is required.

NOTE The skill of the applicator governs whether the sealant is fully wetted onto a clean substrate and correctly tooled. (4.1.3)

4.1.4 Sealant work is not incidental finishing work and shall not be assigned to untrained personnel.

4.2 Source Limitations

4.2.1 For each distinct sealant application, the sealant, its primer, and its backing should be obtained as a compatible system from a single sealant manufacturer's recommendations so that compatibility is established by the party warranting the sealant.

NOTE Mixing a sealant from one source with a primer or backing the sealant manufacturer has not qualified shifts responsibility for an adhesion failure onto the Contractor. (4.2.2)

4.3 Preconstruction Compatibility and Adhesion Testing

4.3.1 Before sealant application begins, the sealant manufacturer shall test the project's actual substrates, primers, and sealants for compatibility and adhesion, either in the manufacturer's laboratory using submitted substrate samples or by the Contractor performing field adhesion tests under the manufacturer's direction.

NOTE Adhesion cannot be assumed from product data alone: the same sealant may bond readily to one mill finish, coating, or stone and fail on another that looks identical. (4.3.2)

4.3.3 Where a test shows inadequate adhesion, the manufacturer shall identify the corrective primer, surface preparation, or alternate sealant before production work proceeds.

4.3.4 The manufacturer shall confirm that the sealant will not be discolored, softened, or have its cure inhibited by contact with the substrate, the primer, the backing, or any adjacent material (such as a coating, a gasket, or a glazing seal) that the sealant will touch, and that none of those materials will be stained by the sealant.

4.3.5 Where a sealant contacts marble, limestone, sandstone, granite, or other porous stone, the sealant shall be verified non-staining for that specific stone, either by the manufacturer's ASTM C1248 test results on the project stone or by a project mock-up held and evaluated for the period the manufacturer specifies.

NOTE Plasticizers and other fluid constituents can migrate out of a sealant into a porous stone and produce a permanent dark halo along the joint; this defect is essentially irreversible, so verification precedes application rather than following it. (4.3.6)

4.4 Mock-Ups

4.4.1 Where directed, the Contractor shall provide a mock-up of representative sealed joints, including the exterior weatherseal joints and any stone or special-substrate joints, for review of color, tooling, joint profile, and adhesion.

4.4.2 Approved mock-ups establish the standard of workmanship for the work.

5 Environmental and Service Conditions

5.1 Application Temperature and Humidity Limits

Application Temperature Rangerange

°F

20406080100120

5.1.1 Sealants shall be applied only within the substrate and ambient temperature and humidity range the manufacturer permits for that product.

NOTE Sealant applied below the minimum temperature may not cure or wet the substrate properly; applied to a substrate at or below the dew point, it bonds to a film of condensation rather than to the substrate. (5.1.2)

NOTE Moisture-cure sealants (most silicones and silyl-terminated polymers) require ambient humidity to cure, while some require a minimum temperature for an acceptable cure rate. (5.1.3)

5.1.4 A working joint shall not be sealed when it is at its widest (cold) or narrowest (hot) dimension.

5.1.5 The sealant cures to whatever width exists at the moment of application and must then accommodate movement in both directions from that cured state.

NOTE A joint sealed wide open on a cold morning is placed almost entirely in compression as the structure warms; sealed tight on a hot afternoon, it is placed almost entirely in extension as it cools. (5.1.6)

NOTE Sealing near the mid-range temperature divides the available movement capability between extension and compression. (5.1.7)

5.2 Movement, Ultraviolet, and Chemical Exposure

NOTE Exterior sealants are exposed continuously to solar ultraviolet radiation, thermal cycling, wind-driven rain, and pollutants, and they must accommodate the cyclic joint movement that those same temperature swings produce. (5.2.1)

5.2.2 The sealant chemistry shall be selected for the exposure: silicone offers the best long-term ultraviolet and weathering resistance for unprotected exterior joints, while urethanes offer superior abrasion and tear resistance for traffic-bearing joints.

5.2.3 Sealants in joints subject to continuous water immersion or to chemical contact shall be qualified for that service (ASTM C1247 for immersion).

6 Sealant Materials and Classification

6.1 ASTM C920 Classification

NOTE Elastomeric sealants are classified under ASTM C920 by a four-part designation — Type, Grade, Class, and Use — that fully describes the product's configuration and capability. (6.1.1)

NOTE Specifying by the ASTM C920 classification rather than by chemistry alone ties the requirement to a measured performance level that multiple manufacturers can meet. (6.1.2)

6.1.3 Type (Component Configuration)

NOTE Type S is a single-component sealant supplied ready to use; Type M is a multi-component sealant mixed before application. (6.1.3.1)

6.1.3.2 The sealant type shall be specified as single-component or multi-component, selected for the joint configuration and application method required.

Sealant Type (ASTM C920)radio

● Type S — single component (standard)

○ Type M — multi-component (fast/uniform cure, deep or high-volume joints)

NOTE Single-component sealants are simpler in the field and dominate building joints; multi-component sealants cure independently of ambient humidity and are used for fast cure, deep joints, and high production. (6.1.3.3)

6.1.4 Grade (Sag Resistance)

NOTE Grade NS is a non-sag (gunnable) sealant that stays in place on vertical and overhead joints; Grade P is a pourable, self-leveling sealant for horizontal joints. (6.1.4.1)

6.1.4.2 The sealant grade shall be specified as non-sag or pourable, matched to the orientation of the joint being sealed.

Sealant Grade (ASTM C920)radio

● Grade NS — non-sag, for vertical and overhead joints (standard)

○ Grade P — pourable / self-leveling, for horizontal joints

NOTE The grade is dictated by joint orientation: a non-sag sealant in a horizontal joint will not self-level, and a self-leveling sealant on a vertical joint will run. (6.1.4.3)

6.1.5 Class (Movement Capability)

NOTE The Class is the sealant's movement capability, established by adhesion and cohesion testing under cyclic movement per ASTM C719. (6.1.5.1)

NOTE A Class 25 sealant withstands ±25% of the joint width; Class 50 withstands ±50%; Class 100/50 withstands +100%/−50%; lower classes are 35, 25, and 12.5. (6.1.5.2)

6.1.5.3 The sealant movement class shall be specified, sized to the anticipated movement the joint is designed to accommodate.

Sealant Movement Class (ASTM C920 / C719)select

Class 100/50 — +100% / −50% (maximum movement, narrow active joints)

Class 50 — ±50% (high-movement exterior weatherseal)

Class 35 — ±35%

Class 25 — ±25% (standard exterior and perimeter joints)

Class 12.5 — ±12.5% (low-movement and interior joints)

NOTE The required class is driven by how much the joint moves relative to its width: the wider the joint relative to the anticipated movement, the lower the class that suffices, but selecting too low a class for an active joint guarantees a cohesive or adhesive tear. (6.1.5.4)

NOTE Exterior weatherseal joints between dissimilar materials are commonly Class 50 to tolerate large differential movement in narrow joints. (6.1.5.5)

6.1.6 Use (Intended Service)

NOTE The Use designations identify the substrates and service the sealant is qualified for, including Use T (traffic-bearing), Use NT (non-traffic), Use I (immersion), Use M (mortar/masonry), Use G (glass), Use A (aluminum), and Use O (other specified substrates). (6.1.6.1)

6.1.6.2 The Use shall match the joint's substrates and service.

Sealant Use (ASTM C920)checkbox

☑ Use NT — non-traffic

☐ Use T — traffic-bearing

☐ Use I — immersion

☐ Use M — mortar / masonry

☐ Use G — glass

☐ Use A — aluminum / coated metal

☐ Use O — other substrate (stone, plastic, as specified)

6.2 Sealant Modulus

NOTE Modulus is the stress a sealant develops as it is strained. (6.2.1)

NOTE A low-modulus sealant exerts low pulling force on the joint faces at a given movement, which is important where the substrate is weak or porous — a high-modulus sealant on soft stone or weak mortar can pull the substrate apart (cohesive substrate failure) before the sealant itself fails. (6.2.2)

6.2.3 Low-modulus sealants shall be used on stone, weak masonry, and joints with large movement.

Sealant Modulusradio

● Low modulus — for stone, masonry, and high-movement joints (standard exterior)

○ Medium modulus — general purpose on sound substrates

○ High modulus — traffic-bearing and abrasion-resistant joints

6.2.4 Medium- or high-modulus sealants suit strong substrates and traffic joints.

6.3 Sealant Chemistry

NOTE The base chemistry determines weathering, cure, adhesion, and staining behavior. (6.3.1)

6.3.2 The chemistry shall be selected for the exposure and substrate, not chosen for cost alone.

6.3.3 Silicone — Neutral Cure vs. Acid (Acetoxy) Cure

NOTE Silicone offers the best ultraviolet and long-term weathering resistance and the widest service-temperature range, making it the default for exposed exterior weatherseal joints. (6.3.3.1)

NOTE Neutral-cure silicone (oxime or alkoxy) is used on masonry, stone, metal, and coated substrates because its cure by-products do not corrode metal or attack masonry. (6.3.3.2)

6.3.3.3 Acid-cure (acetoxy) silicone releases acetic acid as it cures, which can corrode some metals, etch masonry, and stain stone; its use is limited to glass and other non-reactive substrates, typically interior glazing.

Silicone Cure Systemradio

● Neutral cure (oxime/alkoxy) — non-corrosive, for masonry, stone, metal (standard)

○ Acid cure (acetoxy) — for glass and non-reactive substrates only

6.3.3.4 Standard silicones are not paintable and shall not be used where paint must adhere over the joint.

6.3.4 Non-Staining Low-Modulus Silicone for Porous Stone

NOTE Standard silicones can leave an oily or dark migration stain at the edge of a joint in porous stone. (6.3.4.1)

6.3.4.2 Where a silicone joint abuts marble, limestone, granite, or other porous stone, a non-staining, low-modulus silicone verified for that stone per ASTM C1248 shall be used.

6.3.4.3 A non-staining low-modulus silicone is a distinct formulation, not merely a low-modulus silicone, and shall be confirmed by the manufacturer for the project stone.

6.3.5 Polyurethane — Single- and Multi-Component

NOTE Polyurethane sealants offer excellent abrasion, tear, and cut resistance and good adhesion to concrete, making them the standard for horizontal traffic-bearing and pavement joints. (6.3.5.1)

NOTE Polyurethane sealants are paintable, which suits joints that must match adjacent painted surfaces. (6.3.5.2)

NOTE Single-component urethane is convenient for typical joints; multi-component urethane cures faster and more uniformly in deep joints and high-volume horizontal work. (6.3.5.3)

NOTE Urethanes have shorter ultraviolet life than silicone, so for unprotected exterior weatherseal joints silicone or a hybrid is often preferred. (6.3.5.4)

6.3.6 Silyl-Terminated Polyether / Polymer Hybrid (STPe / MS)

NOTE Hybrid sealants based on silyl-terminated polyether or modified-silane polymers combine much of silicone's weathering resistance with urethane's paintability and low staining, and they are generally low-modulus and non-staining on stone. (6.3.6.1)

NOTE Hybrid sealants are used where a paintable, non-staining exterior sealant is required, bridging the gap between silicone and urethane. (6.3.6.2)

6.3.7 Acrylic Latex — Interior

NOTE Water-based acrylic latex sealant (ASTM C834) is a low-movement, paintable interior sealant used for filling and concealing small, essentially non-working interior joints and gaps before painting. (6.3.7.1)

6.3.7.2 Acrylic latex has limited movement capability and limited water resistance and shall not be used in exterior weatherseal or working joints.

6.3.8 Sealant Chemistry Selection

Sealant Chemistry by Applicationselect

Neutral-cure silicone — exterior weatherseal, masonry/metal (standard exterior)

Non-staining low-modulus silicone — joints abutting porous stone

Polyurethane (single-component) — perimeter and general joints, paintable

Polyurethane (multi-component) — horizontal traffic and deep joints

Silyl-terminated polyether / polymer hybrid — paintable non-staining exterior

Acrylic latex (ASTM C834) — interior non-working joints, paintable

6.4 Color and Finish

Exposed Sealant Colorselect

Manufacturer standard color to match adjacent material

Custom-matched color

Clear / translucent

6.4.1 Exposed sealant color shall be selected to match or complement the adjacent material.

6.4.2 Concealed sealants and sealants behind finished surfaces need not be color-selected.

6.4.3 Sealant in joints to be painted shall be a paintable chemistry (urethane, hybrid, or latex), since standard silicone will not hold paint.

7 Joint Design and Backing

7.1 Width-to-Depth Ratio (Shape Factor)

NOTE The relationship between a sealant joint's width and the depth of the sealant bead — the shape factor — is the single most important geometric property of a working joint. (7.1.1)

NOTE For a properly proportioned joint, the sealant is installed in an hourglass profile that is wider at the bonded faces than at its thin mid-section, so that as the joint moves, the strain concentrates in the thinner middle and the bond lines at the faces are relatively protected. (7.1.2)

NOTE A bead that is as deep as it is wide (a near-square cross-section) develops high stress at the bond lines under the same movement and tears loose. (7.1.3)

7.1.4 As a general rule for working joints in the common width range, the sealant depth at mid-joint shall be approximately half the joint width, within the manufacturer's stated limits, with minimum and maximum bead depths the manufacturer specifies for the chosen sealant.

Sealant Width-to-Depth Ratio (working joints)radio

● 2:1 width-to-depth (sealant depth ≈ half joint width) (standard working joints)

○ 1:1 with maximum depth limit (narrow joints, per manufacturer)

○ Per manufacturer for the specific sealant and joint width

7.1.5 A working joint shall be wide enough that the anticipated movement is within the sealant's movement class at that width, and not so wide that the bead sags or exceeds the sealant's maximum.

Typical Exterior Working Joint Widthrange

in.

0.252

Default: 0.5 in.

Per drawings

7.1.6 Joint widths are as detailed on the drawings and are sized from the calculated thermal and structural movement and the selected sealant's movement class per ASTM C1193.

7.2 Two-Sided Adhesion and the Bond Breaker

Back-of-Joint Bond Breakerradio

● Closed-cell or bi-cellular backer rod serving as backing and bond breaker (standard)

○ Bond-breaker tape at back of joint where depth is too shallow for backer rod

7.2.1 A working joint sealant shall bond only to the two opposing joint faces and shall be free to stretch and compress across the gap between them.

7.2.2 A working joint sealant must not bond to the back of the joint, because a sealant adhered on three sides cannot deform freely: instead of stretching across an unbonded span, it is restrained at the back and tears either from a face (adhesive failure) or through itself (cohesive failure).

7.2.3 Two-sided adhesion is achieved with a backer rod (which is also a bond breaker) or, where a backer rod will not fit, with a bond-breaker tape applied to the back of the joint.

7.3 Sealant Backing (Backer Rod)

NOTE Cylindrical sealant backing conforming to ASTM C1330 limits how deep the sealant is installed, establishes the hourglass shape, and acts as a bond breaker at the back of the joint. (7.3.1)

7.3.2 The backer rod shall be sized larger than the joint width — typically about 25% oversize — so it is compressed into the joint and stays in place without being stretched.

Backer Rod Oversize (compression fit)range

% larger than joint width

10253350

7.3.3 The backer rod shall be installed at the depth that produces the specified sealant bead depth.

7.3.4 The backer rod shall not be punctured during installation.

NOTE A punctured closed-cell rod can outgas and bubble the curing sealant. (7.3.5)

7.3.6 Backer Rod Cellular Type

NOTE The cellular structure of the rod is selected for the joint. (7.3.6.1)

NOTE Closed-cell polyethylene backing (ASTM C1330 Type C) resists water absorption and suits most joints but can outgas through a puncture. (7.3.6.2)

NOTE Open-cell backing absorbs water and is limited to dry, vertical joints. (7.3.6.3)

NOTE Bi-cellular backing (ASTM C1330 Type B) has a closed skin over a partly open structure and tolerates surface puncture without outgassing, making it a robust general choice. (7.3.6.4)

7.3.6.5 Open-cell rod shall not be used where water can reach it.

Sealant Backing Type (ASTM C1330)radio

● Closed-cell (Type C) polyethylene — water-resistant, general exterior (standard)

○ Bi-cellular (Type B) — closed skin, tolerant of surface puncture

○ Open-cell (polyurethane) — dry vertical interior joints only

8 Sealant Schedule by Joint Location

NOTE The sealant, primer, and backing for each joint are selected from the materials above according to the joint's location, substrates, movement, and exposure. (8.1)

NOTE The schedule below describes the categories of joints this standard covers and the controlling selection criteria; the specific product for each is recorded in the joint-sealant schedule submittal. (8.2)

NOTE Fire-resistive and smoke-rated joints are not included here and are covered by FirestoppingFirestoppingResolves to the current edition.sync/firestopping. (8.3)

8.4 Exterior Vertical Weatherseal Joints

8.4.1 Joints between dissimilar exterior wall materials — masonry to metal, precast to glass, panel to frame — are weatherseal joints that must keep water and air out while accommodating differential movement between the two materials.

Exterior Vertical Weatherseal Sealantselect

Low-modulus neutral-cure silicone, Class 50, Use NT (standard)

Silyl-terminated polyether / hybrid, Class 50, paintable

Single-component polyurethane, Class 25–50, paintable

8.4.2 Exterior vertical weatherseal joints between dissimilar materials shall be sealed with a low-modulus neutral-cure silicone or hybrid of Class 50 or higher, over a closed-cell or bi-cellular backer rod, with two-sided adhesion.

8.4.3 Coordinate exterior vertical weatherseal joints with Sheet Metal Flashing And TrimSheet Metal Flashing and TrimResolves to the current edition.sync/sheet-metal-flashing-and-trim where the joint meets flashing and with Unit MasonryUnit MasonryResolves to the current edition.sync/unit-masonry at masonry edges.

8.5 Expansion and Control Joints in Concrete and Masonry

NOTE Expansion and control joints accommodate the structure's planned movement and shrinkage. (8.5.1)

8.5.2 Vertical expansion and control joints shall take a non-sag low-modulus sealant of a class matched to the joint movement; horizontal non-traffic joints shall take a self-leveling sealant.

Concrete / Masonry Expansion-Control Joint Sealantselect

Low-modulus silicone or hybrid, Class 50, Use M (standard masonry/concrete)

Single-component polyurethane, Class 25, Use M

Self-leveling (Grade P) sealant for horizontal non-traffic joints

8.5.3 On masonry, a non-staining low-modulus sealant (Use M) shall be used to protect the masonry from edge staining and from being torn by a high-modulus bead.

8.6 Perimeter of Openings

NOTE Joints around windows, doors, louvers, and other openings seal the gap between the frame and the surrounding construction against air and water. (8.6.1)

8.6.2 Perimeter-of-opening joints are weatherseal joints and shall be sealed with a low-modulus silicone or hybrid compatible with both the frame finish (often coated aluminum, Use A) and the wall substrate.

Opening Perimeter Sealantselect

Low-modulus neutral-cure silicone, Class 50, Use A + Use M (standard)

Silyl-terminated polyether / hybrid, paintable, Class 50

Single-component polyurethane, Class 25, paintable

8.6.3 Coordinate perimeter-of-opening joints with Air BarriersAir BarriersResolves to the current edition.sync/air-barriers so the perimeter seal is continuous with the air- and water-resistive barrier.

8.7 Interior Acoustical and General Joints

NOTE Acoustical sealant seals the perimeter and penetrations of sound-rated partitions to prevent flanking sound through gaps; it is a non-hardening, non-skinning sealant that stays flexible to maintain the seal. (8.7.1)

8.7.2 The perimeter and penetrations of sound-rated partitions shall be sealed with a non-hardening, non-skinning acoustical sealant that stays flexible to maintain the seal.

Interior Sealantselect

Acrylic latex (ASTM C834) — paintable, non-working interior joints (standard)

Non-hardening acoustical sealant — perimeter of sound-rated partitions

Single-component polyurethane — interior joints subject to movement or moisture

8.7.3 General interior non-working joints and gaps before paint shall be filled with paintable acrylic latex (ASTM C834).

8.7.4 Coordinate acoustical sealing with Gypsum Board AssembliesGypsum Board AssembliesResolves to the current edition.sync/gypsum-board-assemblies.

8.8 Horizontal Traffic-Bearing Joints

8.8.1 Joints in walkways, plazas, decks, and pavement carry foot or vehicular traffic and must resist abrasion, tearing, and indentation while remaining watertight.

Horizontal Traffic Joint Sealantselect

Multi-component polyurethane, self-leveling, Use T (standard traffic joints)

Single-component polyurethane, Use T, for light foot traffic

Traffic-grade silicone, Use T, where UV exposure governs

8.8.2 Horizontal traffic-bearing joints shall take a self-leveling or non-sag traffic-grade sealant of Use T — typically a multi-component polyurethane — installed slightly recessed below the surface so traffic does not abrade the bead.

8.8.3 Coordinate horizontal traffic joints with Membrane RoofingMembrane RoofingResolves to the current edition.sync/membrane-roofing where a traffic joint occurs over a roofing or deck membrane.

9 Installation

9.1 Surface Preparation

Non-Porous Substrate Cleaningradio

● Two-cloth solvent wipe (apply with one cloth, wipe dry with a second) (standard)

○ Per sealant manufacturer's substrate-specific cleaning procedure

9.1.1 Joint substrates shall be cleaned of dust, dirt, oil, grease, frost, surface laitance, old sealant, coatings that interfere with adhesion, and any other contaminant that would prevent the sealant from wetting and bonding to a sound surface, in accordance with ASTM C1193 and the sealant manufacturer's instructions.

9.1.2 Porous substrates (concrete, masonry, stone) shall be cleaned dry, by brushing, grinding, or blowing out with oil-free air.

9.1.3 Non-porous substrates (metal, glass, coated frames) shall be solvent-cleaned using the two-cloth method, in which one cloth applies the solvent and a second clean cloth wipes it off before it evaporates, so that dissolved contaminants are removed rather than redeposited.

9.1.4 Cleaning shall be completed shortly before priming and sealing so the surface does not re-soil.

9.2 Priming

Primer Requirementradio

● Prime where required by manufacturer / adhesion test, per substrate (standard)

○ Prime all substrates

○ No primer (only where manufacturer confirms adhesion without primer)

9.2.1 Primer shall be applied where the sealant manufacturer requires it for the substrate, as a thin, uniform coat to the joint faces only (not across the area to be left unsealed), and allowed to dry for the manufacturer's stated time before the backing and sealant are installed.

NOTE Primer chemically prepares the substrate so the sealant bonds; many sealant-substrate pairs that fail without primer pass readily with the correct primer. (9.2.2)

9.2.3 Whether a primer is required, and which primer, shall be established by the preconstruction adhesion testing rather than assumed.

9.3 Backing Installation

9.3.1 The backer rod shall be installed by rolling it into the joint to the depth that produces the specified sealant bead depth, without twisting, stretching, or puncturing it, using a blunt tool.

9.3.2 Where the joint is too shallow for a backer rod, bond-breaker tape shall be applied to the back of the joint instead.

9.3.3 The backing shall be in place before sealant application so the sealant forms the intended profile against it and does not bond to the back of the joint.

9.4 Masking

9.4.1 Edges adjacent to exposed sealant joints shall be masked with tape where necessary to produce a clean, straight sealant line and to protect the adjacent surfaces, particularly on porous substrates where excess sealant would stain.

9.4.2 Masking tape shall be removed immediately after tooling, while the sealant is still uncured, so the tooled edge is not disturbed.

9.5 Sealant Application and Tooling

9.5.1 Sealant shall be gunned into the prepared joint in a continuous operation that fully wets both joint faces and fills the joint against the backing without entrapping air, then immediately tooled with light pressure to force the sealant against the faces, consolidate it, eliminate voids, and form the slightly concave hourglass profile.

NOTE Tooling is not cosmetic: the pressure of tooling is what drives the sealant into intimate contact with the substrate and develops the bond. (9.5.2)

9.5.3 Dry tooling is preferred; tooling agents that could contaminate the bond line or be left on the substrate shall not be used unless the manufacturer approves them.

9.5.4 Sealant shall not be applied over an uncured or skinned-over previous bead or onto a wet or frosted substrate.

10 Field Quality Control

10.1 Field Adhesion Testing

Field Adhesion Test Frequency (ASTM C1521)select

One test per floor per building elevation, minimum (standard)

One test per fixed lineal interval of installed joint

Per drawings — project-specific quality plan

10.1.1 After the sealant has cured, field adhesion of installed weatherproofing sealant joints shall be tested per ASTM C1521 to verify that the sealant has bonded to both joint faces.

NOTE In the common hand-pull (tail) method, a length of sealant is cut loose and pulled back by hand; a passing joint exhibits cohesive failure (the sealant tears within itself) rather than adhesive failure (the sealant peels cleanly off the substrate), demonstrating that the bond to the substrate is stronger than the sealant. (10.1.2)

10.1.3 Joints that fail adhesively shall be cut out, the substrate re-prepared and primed as the corrective testing directs, and the joint re-sealed and re-tested.

10.1.4 Each location where sealant is cut for a destructive adhesion test shall be repaired by re-priming and re-sealing it to match the surrounding joint, so the test does not leave an unsealed gap.

11 Cleaning and Protection

11.1 Excess and misapplied sealant and smears shall be removed from adjacent surfaces as the work proceeds, by the method the sealant manufacturer recommends for the substrate, before the sealant cures.

NOTE Cured sealant on porous stone or a finished surface is difficult to remove without damage. (11.2)

11.3 Completed joints shall be protected from traffic, abrasion, and contamination until the sealant has cured.

11.4 Damaged or contaminated sealant shall be removed and replaced.

12 Delivery, Storage, and Handling

12.1 Sealants, primers, and backings shall be delivered in the manufacturer's original unopened containers bearing the product identification, lot number, and shelf-life or expiration date.

12.2 Sealants, primers, and backings shall be stored within the temperature range the manufacturer specifies, out of direct sunlight and protected from freezing where the product requires it.

12.3 Sealant has a finite shelf life; material that has exceeded its expiration date or that has been frozen or heat-damaged shall not be used.

NOTE An aged or damaged sealant may not cure or develop its rated movement capability. (12.4)

12.5 Stock shall be rotated so the oldest in-date material is used first.

13 Warranty

Sealant Warrantyradio

● Two-year Contractor warranty plus manufacturer materials warranty (standard)

○ Special manufacturer weatherproofing warranty (extended term, exterior weatherseal)

13.1 Contractor Warranty

13.1.1 The Contractor shall warrant the sealant work against defective materials and workmanship — including loss of adhesion or cohesion, leakage, and failure to cure — for a period of not less than two years from substantial completion, or for the period stated in the contract documents if longer, and shall remove and replace defective sealant at no cost to the Owner.

13.2 Manufacturer Materials Warranty

13.2.1 The sealant manufacturer shall provide its standard materials warranty for the sealant.

13.3 Special Weatherproofing Warranty

13.3.1 Where required for exterior weatherseal joints, the sealant manufacturer shall provide a special weatherproofing warranty covering the watertightness and adhesion of the installed sealant for an extended term — commonly up to 20 years — issued on the basis that an approved applicator installed an approved sealant system over substrates the manufacturer qualified by adhesion testing.

NOTE The longer manufacturer warranty depends on the applicator approval, compatibility testing, and field adhesion testing required above being met during construction, so they are prerequisites to it. (13.3.2)