1 Scope
NOTE This standard governs cold-applied elastomeric sealants used to weatherproof the exterior building envelope at perimeter, transition, and penetration joints. (1.1)
NOTE It applies to both new construction and the restoration or recaulking of existing commercial and institutional buildings. (1.2)
NOTE The following exterior joint conditions are within scope: window and curtain wall perimeter joints (frame-to-wall), door frame perimeters, above-grade control and expansion joints in concrete, masonry, metal panel, EIFS, and wood-framed walls, through-wall penetrations such as pipes, conduit, and louvers, thresholds, and horizontal ledge joints. (1.3)
NOTE Single-component and multicomponent silicone, polyurethane, and polyurethane-hybrid sealant systems, together with backer rods, bond-breaker tape, and primers, are within scope. (1.4)
NOTE The following work types are excluded from this standard: (1.5)
- Interior joint sealants, acoustical sealants, and fire-rated through-penetration seals — coordinate assembly ratings with Fire Rated Wall And Floor Assemblies.
- Structural glazing sealants and structural silicone curtain wall perimeter joints — see Glazed Curtain Walls.
- Aluminum storefront and entrance frame perimeter sealants furnished as part of the glazing system package — see Aluminum Entrances And Storefronts.
- Building expansion joint cover assemblies (cover plates, precompressed foam, bellows) — see Expansion Joints.
- The broader non-weatherproofing sealant vocabulary (acoustical, setting beds, paint caulk) — see Joint Sealants; this standard is the narrower exterior-weatherproofing subset.
- Horizontal traffic-bearing pavement joint sealants (parking deck, highway), which fall outside the ASTM C920 scope addressed here.
- Roofing-membrane flashings and fluid-applied roof coatings at base-of-wall — see Fluid Applied Roofing.
2 Referenced Standards
2.1Materials and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard |
Title |
| ASTM C920-18(2024) |
Standard Specification for Elastomeric Joint Sealants |
| ASTM C1193-25 |
Standard Guide for Use of Joint Sealants |
| ASTM C1248-12(2018) |
Standard Test Method for Staining of Porous Substrate by Joint Sealants |
| ASTM C1481-12(2024) |
Standard Guide for Use of Joint Sealants with Exterior Insulation and Finish Systems (EIFS) |
| ASTM C794-18 |
Standard Test Method for Adhesion-in-Peel of Elastomeric Joint Sealants |
| ASTM C1401-14(2019) |
Standard Guide for Structural Sealant Glazing |
| ASTM C679-20 |
Standard Test Method for Tack-Free Time of Elastomeric Sealants |
| ASTM C1516-06(2019) |
Standard Guide for Selection of Sealants for Use in Air Barrier Systems |
| AAMA 800-15 |
Voluntary Specifications and Test Methods for Sealants (includes AAMA 808.3) |
NOTE ASTM C920 is the controlling product specification and classifies every elastomeric sealant by Type, Grade, Class, and Use; specifying that classification, not a bare reference to C920, is the foundation of a usable sealant specification. (2.3)
NOTE ASTM C1193 is the companion installation guide governing joint design, substrate preparation, priming, backer rod selection, tooling, and field quality control; it is cited throughout this standard for the "how" behind the requirements. (2.4)
3 Submittals
3.1The Contractor shall submit the following Action Submittals for review before ordering or installing any sealant:
- Product data sheets for each sealant, primer, backer rod, and bond-breaker tape, including the manufacturer's ASTM C920 Type, Grade, Class, and Use designations.
- Manufacturer's color chart, and a custom-color request where a factory-matched or custom-tinted color is required.
- Joint design schedule correlating each joint type to its sealant product, movement class, joint width, and backer rod.
- Substrate compatibility and adhesion test data, or the manufacturer's written confirmation of primer requirements, for each project-specific substrate.
- Manufacturer's approved-sealant list confirmation where AAMA 800 compatibility with the fenestration system is required.
☐ Product data (sealant, primer, backer rod, tape)
☐ Color chart and custom-color request
☐ Joint design schedule
☐ Substrate compatibility / adhesion test data
☐ Fenestration manufacturer approved-sealant confirmation
3.2The Contractor shall submit the following Informational Submittals:
- Field adhesion (peel) test reports for each substrate at project startup and at the intervals scheduled below.
- Sample warranty for the installed sealant system.
- Applicator qualification statement documenting comparable completed projects.
☐ Field adhesion (peel) test reports
☐ Sample warranty
☐ Applicator qualification statement
3.3The Contractor shall submit the following Closeout Submittals before final acceptance:
- Executed sealant manufacturer's warranty and the installer's workmanship warranty.
- As-installed joint locations and product log keyed to the joint design schedule.
- Maintenance instructions for inspection and recaulking intervals.
☐ Executed manufacturer and installer warranties
☐ As-installed joint and product log
☐ Maintenance / recaulking instructions
4 Quality Assurance
4.1Installer qualifications
4.1.1The sealant installer shall have completed at least three exterior weatherproofing-sealant projects of comparable scope within the preceding five years.
4.1.2The installer shall employ workers trained in the specific sealant systems used on the project, including manufacturer field instruction where required to validate the warranty.
4.2Mock-ups and field adhesion testing
NOTE Field adhesion verification is the single most reliable defense against the adhesion failures that account for roughly 40% to 50% of all sealant warranty claims; it confirms in place what a data sheet only promises in the laboratory. (4.2.1)
4.2.2The Contractor shall perform a field-applied mock-up of each representative joint condition and obtain acceptance before production sealant work begins.
4.2.3The Contractor shall perform a field adhesion (peel) test in accordance with ASTM C1193 at the start of work, at each new substrate first encountered, and at the scheduled production interval below.
NOTE A cohesive failure mode, in which the sealant tears within itself rather than releasing from the substrate, is the passing result; an adhesive failure, in which the sealant releases cleanly from the substrate, is a failing result requiring corrective action. (4.2.4)
4.2.5Sealant that fails the field adhesion test shall be removed and the substrate re-prepared, re-primed, and re-sealed before work continues at that condition.
5 Environmental and Service Conditions
5.1Application temperature
NOTE Sealant shall be applied only when the substrate surface temperature is within the manufacturer's published application range; substrate surface temperature, not air temperature, governs whether application may proceed. (5.1.1)
5.1.2Single-component polyurethanes shall not be applied below 40°F (4°C) substrate surface temperature unless the manufacturer's data sheet permits a lower limit.
5.1.3Sealant shall not be applied when the substrate surface temperature exceeds 100°F (38°C), above which cure rates and tooling behavior of single-component silicone are impaired.
5.2Service temperature range
NOTE Selected sealants must remain elastic across the full service temperature swing the joint will see; silicone retains elasticity over a far wider range than polyurethane, which is one reason it is preferred at sun-loaded aluminum frames. (5.2.1)
5.2.2Silicone sealants shall maintain published movement capability over a service temperature range of at least -65°F to +400°F (-54°C to +204°C).
5.2.3Polyurethane sealants shall maintain published movement capability over a service temperature range of at least -40°F to +180°F (-40°C to +82°C).
5.3Cure and weather exposure
NOTE Tack-free time per ASTM C679 is the point at which the sealant surface will shed water and resist dirt pickup, but it is not full cure; deep joints continue curing for days and must be protected accordingly. (5.3.1)
5.3.2Freshly placed sealant shall be protected from rain and standing water until it reaches tack-free condition per ASTM C679.
5.3.3Joints shall not be subjected to building movement, traffic, or hydrostatic exposure until the sealant has reached full cure per the manufacturer's data sheet.
6 Sealant Selection and Classification
6.1The ASTM C920 classification system
NOTE Specifying a sealant by ASTM C920 alone, without Type, Grade, Class, and Use, leaves the entire product selection to the contractor and generates an RFI on every product submittal; the classification fields below are mandatory, not optional refinements. (6.1.1)
NOTE Type designates component count: Type S is single-component (cures by reaction with atmospheric moisture); Type M is multicomponent (cures by mixing two parts and offers a longer working pot life for large restoration and deck joints). (6.1.2)
NOTE Grade designates flow: Grade NS (non-sag) holds its shape on vertical and overhead joints; Grade P (pourable, self-leveling) flows into horizontal deck and ledge joints. (6.1.3)
NOTE Class designates movement capability, expressed as the joint movement the sealant accommodates: Class 100/50 (+100%/-50%), Class 50, Class 35, Class 25, and Class 12.5, in descending order of movement. (6.1.4)
NOTE Use designates qualified substrate and exposure: T (traffic-bearing horizontal), NT (non-traffic horizontal), I (immersion), M (mortar/masonry), G (glass), A (aluminum), and O (other); a single joint may require several Use designations. (6.1.5)
6.1.6The Contractor shall provide for each joint a sealant whose ASTM C920 Type, Grade, Class, and Use designations match the scheduled values for that joint.
● Type S - single-component
○ Type M - multicomponent
● Grade NS - non-sag (vertical / overhead)
○ Grade P - pourable / self-leveling (horizontal)
Class 100/50
Class 50
Class 35
Class 25
Class 12.5
☐ NT - non-traffic horizontal
☐ T - traffic-bearing horizontal
☐ M - mortar / masonry
☐ A - aluminum
☐ G - glass
☐ O - other substrate
☐ I - immersion
6.2Base polymer (chemistry) selection
NOTE Chemistry choice is driven by three things: the calculated joint movement, whether the surface must be painted, and whether the joint abuts porous stone. Silicone wins on movement and weathering but cannot be painted and may stain stone; polyurethane is paintable and stone-friendly but accommodates less movement. (6.2.1)
NOTE For masonry and concrete perimeter and control joints, the 80%-case default is single-component polyurethane, Type S, Grade NS, Class 25, Use NT/M/A/O. (6.2.2)
NOTE For aluminum frame and metal panel perimeter joints, the 80%-case default is single-component silicone, Type S, Grade NS, Class 50. (6.2.3)
6.2.5The Contractor shall select the base polymer to satisfy simultaneously the movement, paintability, and staining requirements scheduled for the joint.
● Single-component polyurethane (NS)
○ Single-component silicone (NS)
○ Polyurethane-hybrid / modified silicone (paintable)
○ Self-leveling polyurethane (Grade P, horizontal)
○ Multicomponent polyurethane (NS, restoration/deck)
6.3Paintability
NOTE Silicones cannot be painted; paint will not adhere to a cured silicone surface and will fish-eye over it. Where a sealed joint falls within a painted field or will receive paint overspray, a polyurethane or a paintable polyurethane-hybrid must be specified and coordinated with the painting scope. (6.3.1)
6.3.2Where the sealed joint occurs in a surface scheduled to be painted, the Contractor shall provide a paintable polyurethane or polyurethane-hybrid sealant, not silicone.
○ Paintable required (polyurethane / hybrid)
● Not paintable acceptable (silicone permitted)
6.4Non-staining performance at porous stone
NOTE Silicone in contact with limestone, marble, sandstone, or granite can migrate oils into the stone and leave a permanent stain that cannot be removed; the only defense is to verify non-staining performance by test before the sealant ever touches the stone. (6.4.1)
6.4.2Where sealant contacts porous stone, the Contractor shall provide a sealant verified non-staining to that substrate in accordance with ASTM C1248.
○ Required - sealant abuts porous stone
● Not required - no porous stone contact
7 Joint Design and Geometry
7.1Width and depth
NOTE A weatherproofing sealant works by stretching and compressing as the joint moves; that movement capacity comes from the sealant's shape, so the joint geometry is as much a part of the specification as the product. An over-deep, undersized joint cannot move and tears in an hourglass pattern; a correctly proportioned joint flexes freely. (7.1.1)
7.1.2The joint width shall be a minimum of 3/8 in. (10 mm); perimeter joints at aluminum frames are typically 1/2 in. to 3/4 in. (12 mm to 19 mm).
7.1.3Joints wider than 1-1/2 in. (38 mm) shall not be sealed with a field-applied bead alone; use a precompressed foam sealant or expansion joint cover assembly per Expansion Joints. 7.1.4The sealant depth at the bead center shall be one-half the joint width, with a minimum of 1/4 in. (6 mm) and a maximum of 1/2 in. (13 mm) for joint widths up to 1 in. (25 mm), per ASTM C1193.
7.1.5The sealant depth shall not exceed the joint width; a 1:1 width-to-depth ratio is the deepest permitted.
7.2Movement accommodation
7.2.1The selected movement class shall equal or exceed the joint movement calculated from thermal expansion and structural drift for the assembly and climate.
● Class 25 polyurethane - masonry / concrete
○ Class 50 silicone - aluminum frame / metal panel
○ Class 100/50 silicone - high-movement curtain wall
7.3Backer rod and bond breaker
NOTE A sealant that bonds to three sides of a joint, including the back, cannot move; the back-of-joint bond restrains it and it tears at its face. The backer rod (or bond-breaker tape in very shallow joints) exists to break that third-side bond and to tool the bead to its proper hourglass profile. (7.3.1)
NOTE Closed-cell polyethylene backer rod is the default for exterior weatherproofing joints; open-cell polyurethane backer rod is used as an off-gassing bond breaker in deep joints, and bond-breaker tape is used only where the joint is too shallow for any rod. (7.3.2)
7.3.3The Contractor shall install a backer rod or bond-breaker tape in every joint to prevent three-sided adhesion.
7.3.4The backer rod diameter shall be 25% to 33% larger than the joint width so the rod compresses into the joint and cannot be displaced behind the sealant.
7.3.5The backer rod shall not be punctured, stretched, or twisted during installation, as any of these changes its depth and disturbs the bead profile.
● Closed-cell polyethylene
○ Open-cell polyurethane (bond breaker, deep joints)
○ Bond-breaker tape (shallow joints only)
8 Substrate Preparation and Priming
8.1Cleaning
8.1.1The joint substrate shall be clean, dry, sound, and free of dust, oils, form-release agents, old sealant residue, coatings, and frost before any primer or sealant is applied.
NOTE Existing failed sealant in restoration work shall be completely removed and the substrate re-prepared; new sealant applied over old sealant bonds cohesively to the old material and fails at that interface. (8.1.2)
8.1.3In restoration work the Contractor shall remove all existing sealant to sound substrate and re-prepare the joint before applying new sealant.
8.2Priming
NOTE Failure to prime is the most common single cause of adhesion failure, particularly on concrete, CMU, EIFS, and anodized aluminum; primer is cheap and adhesion failure is the most expensive defect in the assembly. (8.2.1)
8.2.2The Contractor shall determine the primer requirement for each substrate from the manufacturer's adhesion testing on the project-specific substrates, not from a generic assumption.
8.2.3Where primer is required, the Contractor shall apply it per the manufacturer's instructions and allow it to dry to tack-free, typically 30 min to 60 min, before placing sealant.
8.2.4Sealant shall be placed within the manufacturer's published open time after the primer dries; a primed surface left exposed too long shall be re-primed.
● Primer required
○ Primer not required (verified by test)
8.3EIFS substrates
NOTE EIFS demands special attention: an incompatible sealant chemically attacks the EPS insulation board, and generic specifications routinely omit the compatibility check that ASTM C1481 requires. (8.3.1)
8.3.2Where the joint abuts an EIFS surface, the Contractor shall provide a sealant and joint design conforming to ASTM C1481 and approved in writing by the EIFS manufacturer.
9 Installation
9.1Application
9.1.1Sealant shall be gun-applied in a continuous operation that fully wets both joint faces and leaves no voids, skips, or air pockets behind the bead.
9.1.2The sealant shall contact solid substrate over a minimum bond width of 3/8 in. (10 mm) on each side of the joint, per ASTM C1193.
9.1.3The bead shall be tooled immediately after application, before skinning, to force the sealant against both joint faces and to form a slightly concave, hourglass profile.
9.1.4Masking tape, where used to produce clean bead edges, shall be removed immediately after tooling and before the sealant skins.
0.3750.75
Default: 0.375 in.
9.2Penetrations and transitions
NOTE Through-wall penetrations, thresholds, and dissimilar-material transitions are where the weather barrier is most often broken; each requires a fully tooled, continuous bead bridging the joint with backer rod behind it, exactly as a field joint does. (9.2.1)
9.2.2The Contractor shall seal each through-wall penetration of pipe, conduit, or louver with a continuous tooled bead.
9.2.3The backer rod used at through-wall penetrations shall be sized to the annular gap between the penetrating element and the sleeve or rough opening.
9.2.4Sealant at horizontal ledge and threshold joints shall be sloped or detailed to shed water and shall not be left in a configuration that ponds water against the bead.
9.3Coordination of perimeter sealant responsibility
NOTE At curtain wall and storefront perimeters, both the glazing installer and the general contractor's sealant crew can claim the perimeter joint, and a joint claimed by no one is the joint that leaks; the specification must name the responsible party unambiguously. (9.3.1)
9.3.2The Contractor shall designate responsibility for the curtain wall and storefront perimeter weatherseal, typically to the glazing installer, and shall reflect that designation in the joint schedule; coordinate with Aluminum Entrances And Storefronts and Glazed Curtain Walls. 9.3.3Perimeter sealant compatibility with architectural aluminum fenestration shall conform to AAMA 800 and to the fenestration manufacturer's approved-sealant list.
10 Field Quality Control
10.1Inspection
10.1.1The Contractor shall inspect every completed joint for full, continuous, void-free fill, correct bead profile, and clean edges.
10.1.2Beads exhibiting gaps, blisters, three-sided adhesion, incorrect profile, or adhesive failure shall be cut out and replaced.
10.2Adhesion verification during production
NOTE Field peel testing must continue into production, not stop after the startup test, because substrate conditions, weather, and workmanship all change as the job proceeds and adhesion can fail on a later wall that passed at startup. (10.2.1)
10.2.2The Contractor shall perform production-stage field adhesion tests at the scheduled interval and shall record the failure mode (cohesive or adhesive) for each.
11 Delivery, Storage, and Handling
11.1Delivery and storage
11.1.1Sealants, primers, and backer rods shall be delivered in unopened original containers bearing the manufacturer's name, product designation, ASTM C920 classification, batch number, and shelf-life expiration date.
11.1.2Materials shall be stored in a dry, shaded location within the temperature range published by the manufacturer and protected from freezing where the data sheet so requires.
11.1.3Sealant whose shelf-life expiration date has passed shall not be used and shall be removed from the site.
11.2Handling
11.2.1Multicomponent sealant shall be mixed strictly per the manufacturer's ratio and mixing-time instructions; under-mixed or off-ratio material will not cure properly.
12 Warranty
12.1Warranty coverage
12.1.1The sealant manufacturer shall warrant the sealant material against adhesive and cohesive failure, and against weathering and color change beyond published limits, for the scheduled term.
12.1.2The installer shall warrant the workmanship of the sealant installation against leakage and adhesive or cohesive failure for the scheduled term.
13 Maintenance and Recaulking
13.1Maintenance program
NOTE Exterior sealant is a wearing element of the envelope, not a permanent one; even a 20-year sealant should be inspected periodically and recaulked at end of service life, and the owner should be told so at closeout. (13.1.1)
13.1.2The Contractor shall provide maintenance instructions identifying recommended inspection intervals and the indicators of sealant end of life (loss of elasticity, surface crazing, adhesive release, and joint leakage).
13.1.3Recaulking of failed joints shall follow the same removal, preparation, priming, backer rod, and tooling requirements as new work; sealant shall not be reapplied over existing failed sealant.