Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
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title: Exterior Weather Sealants
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## Application temperature
−### 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. {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.
### Single-component polyurethanes shall not be applied below 40°F (4°C) substrate surface temperature unless the manufacturer's data sheet permits a lower limit.
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## Service temperature range
−### 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. {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.
### Silicone sealants shall maintain published movement capability over a service temperature range of at least -65°F to +400°F (-54°C to +204°C).
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### 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. {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. {note}
+### For masonry and concrete perimeter and control joints, the default is single-component polyurethane, Type S, Grade NS, Class 25, Use NT/M/A/O. {note}
−### For aluminum frame and metal panel perimeter joints, the 80%-case default is single-component silicone, Type S, Grade NS, Class 50. {note}
+### For aluminum frame and metal panel perimeter joints, the default is single-component silicone, Type S, Grade NS, Class 50. {note}
### Where a high-movement curtain wall perimeter joint requires Class 100/50 performance, a two-part structural silicone may be required; that condition crosses into [[sync/glazed-curtain-walls]] and ASTM C1401 territory and shall be coordinated with the glazing scope. {note}
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### The 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.
−### 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. {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.
### In restoration work the Contractor shall remove all existing sealant to sound substrate and re-prepare the joint before applying new sealant.
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# Installation {toc}
−## Application
+## Sealant 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.
−### Sealant 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.
+## The 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.
−### The 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.
+## The 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.
−### The 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.
+## Masking tape, where used to produce clean bead edges, shall be removed immediately after tooling and before the sealant skins.
−### Masking tape, where used to produce clean bead edges, shall be removed immediately after tooling and before the sealant skins.
−
```datasheet
label: Minimum substrate bond width each side
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## Adhesion verification during production
−### 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. {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.
### The Contractor shall perform production-stage field adhesion tests at the scheduled interval and shall record the failure mode (cohesive or adhesive) for each.
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### Recaulking 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.