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Sealants, compatibility and joint design · Lesson 2 of 4

Sealants, compatibility and joint design: materials, standards and design constraints

The three common sealant families for metal, the silicone rule for bare metal, the order of compatibility checks, the standards map, movement class and temperature limits.

You will be able to: Compare butyl, polyurethane and silicone sealants for metal work, run the compatibility checks in order, and name the standards and specification constraints that govern a joint.

11 min · 10 slides · 9 questions

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Slide 1 of 10

Three common families

MCA lists butyl, polyurethane and silicone as the most common sealant types in metal construction.

Most metal roof manufacturers publish a list of approved sealants, and MCA calls it imperative to follow it.

If a different sealant is planned, MCA says it is best to get approval from the metal roof manufacturer.

Butyl, polyurethane and silicone comparedThree cards compare butyl, polyurethane and silicone sealants on cure, paint, exposure or choice, and whether MCA calls it generally compatible with butyl.Three families used on metalButylCure: stays tackyDo not paint itExposure: small lap end onlyGenerally OK: polyurethanePolyurethaneNearby: let it cure firstPaint: most can be paintedChoose: made for metalGenerally OK: butylSiliconeCure: neutral cure onlyPaint: most cannot be paintedSome RTV can rust GalvalumeGenerally not: butylMCA technical bulletin, 2020

Three cards compare butyl, polyurethane and silicone sealants on cure, paint, exposure or choice, and whether MCA calls it generally compatible with butyl.

Statements from the Metal Construction Association technical bulletin (06/2020). Its service-life and movement figures are not repeated here.

Sources

Videos for this lesson

What this video shows: A metal panel supplier’s channel. Its description covers gun caulking against butyl tape sealant, curing characteristics, colors and testing, and tells viewers to check the manufacturer’s details.

Video: What is Metal Roofing & Wall Sealant? Types, Uses, Applications by The Metal Roofing Channel, on YouTube. AFS checked its description against this lesson.

Glossary

Butyl sealant
A generally non-curing, non-skinning sealant that stays flexible and tacky, made as tube or tape. MCA says it is not a topical sealant and should not be exposed to prolonged sunlight.
Neutral-cure silicone
The kind of silicone MCA says to use on metal construction. Some RTV silicones instead contain acetic acid, which will cause bare metals such as Galvalume to rust.
Acetoxy-cure silicone
A silicone that releases acetic acid while curing. AFS’s own note says it is not compatible with copper or lead-coated copper.
Polyurethane sealant
A sealant MCA lists among the three common types for metal. Use only a polyurethane designed specifically for metal and confirmed not to initiate or accelerate corrosion.
Hybrid sealant
A sealant the sample UFGS offers as an optional Class 50 choice where thermal movement may be an issue or dissimilar substrates meet.
Substrate
The surface a sealant bonds to. The sample VA specification lists metal, glass and porcelain enamel among nonporous substrates, and concrete and masonry among porous ones.