The wrong sealant in the right joint still fails — silicone, polyurethane, and hybrid sealants have genuinely different strengths, and choosing by chemistry rather than by habit is what makes a joint last.
Sealant is a small line item that fails more often than almost any other envelope component, and a large share of those failures come from choosing the wrong chemistry for the joint. The three families used most on buildings — silicone, polyurethane, and hybrid (including STPE) — behave differently in weathering, movement capability, paintability, abrasion resistance, and adhesion. A silicone that excels on a weatherseal may be wrong where the joint must be painted; a polyurethane that suits a traffic joint may not match a highly-exposed one. Choosing by chemistry, not by what is on the truck, is what makes a joint last.
The value is in the chemistry. The sections below cover the four aspects that matter most — silicone sealants, polyurethane sealants, hybrid and STPE sealants, and matching sealant to the joint — and how ACE approaches sealant selection.
These challenges rarely stay in one silo: the same discipline runs through the same playbook behind air barrier types, lessons from rigid insulation types, and our guidance on metal composite panel systems, and it all ladders up to ACE’s broader remedial waterproofing and repair.
Silicone sealants are a leading choice for exposed weatherseals, because silicone chemistry offers excellent UV and weather resistance and high movement capability, holding up on highly-exposed facade joints and glazing weatherseals where sun and movement are severe. Long-term weathering and movement performance are silicone’s central strengths.
The main trade-offs are that most silicones cannot be painted and can attract dirt or affect adjacent surfaces, so they are chosen where their weathering and movement advantages outweigh those limitations.
Because silicone excels precisely where exposure and movement are hardest, it is often the right chemistry for weatherseals and structural or glazing applications, provided its paint and staining behavior are acceptable there.
Representative of the factors ACE weighs in sealant selection. Illustrative distribution, not a published statistic.
Polyurethane sealants suit a different set of joints, because polyurethane chemistry is paintable and offers good abrasion and tear resistance, making it well-suited to joints that must be painted or that see wear, such as many horizontal and traffic-adjacent joints. Paintability and toughness are polyurethane’s defining advantages.
Its trade-off is generally lower long-term UV and weathering durability than silicone, so it is better matched to protected, painted, or wear-exposed joints than to the most severely sun-exposed ones.
Because polyurethane pairs paintability and abrasion resistance, it fits joints where those matter more than maximum weathering life, which is a different niche from silicone rather than a lesser one.
A sealant is chosen by habit rather than chemistry, so an exposed or painted or high-movement joint gets the wrong product and fails early.
Select among silicone, polyurethane, and hybrid sealants by the joint’s movement, exposure, substrate, and finish, and verify adhesion on the real materials.
The chemistry fits the joint, the sealant weathers and moves and bonds as needed, and the frequent early failures are avoided.
Hybrid and STPE sealants (silyl-terminated polyethers and similar) aim to combine strengths, because these newer chemistries offer good weathering and movement along with paintability and strong adhesion, often without isocyanates and with lower VOC, which is why they have grown in use. Blending durability with paintability and adhesion is their appeal.
They can bridge cases that once forced a choice between silicone’s weathering and polyurethane’s paintability, and their broad adhesion can simplify substrate compatibility, though specific products still have to be verified for the application.
Because hybrids occupy a middle ground with broad utility, they are an increasingly common default where a single sealant must weather well, be painted, and adhere to varied substrates.
Get the sealant chemistry matched to the joint's movement, exposure, substrate, and finish.
Schedule a consultationCall (866) 389-8883Matching sealant to the joint is the decision that ties the chemistries together, because the right sealant depends on the joint’s movement range, exposure, substrates, whether it will be painted, and compatibility with adjacent materials. Choosing the chemistry that fits all of those, and confirming adhesion to the actual substrates, is what makes the joint last.
Substrate compatibility and adhesion are decisive, since even the right chemistry fails if it does not bond to the specific substrates, which is why field adhesion testing on the real materials is valuable.
The most valuable point overall is that sealant is chosen by chemistry and joint conditions, not by habit — silicone, polyurethane, and hybrid each fit particular joints, and matching the chemistry to the joint is what prevents the frequent, avoidable sealant failures seen on buildings.
In ACE’s field work, most sealant types and chemistry problems trace back to a few recurring locations — Movement & exposure, Substrate adhesion & compatibility, and Paintability & finish — rather than the open field of the wall or roof. The cost of resolving them climbs by roughly an order of magnitude at each stage: a detail corrected during design costs a fraction of the same fix during construction, which is itself far cheaper than a repair once the facility is operating. That economics is why we push envelope decisions as early in the project as possible.
Weigh silicone, polyurethane, and hybrid sealants against the joint's movement range, exposure, substrates, paint needs, and material compatibility.
Confirm the chosen sealant adheres to the actual substrates, since even the right chemistry fails without adhesion, and field adhesion testing verifies it.
Ensure proper joint design, backer rod, and tooling so the chosen sealant can move and bond as its chemistry allows.
Fill out the form below and we'll get back to you within 24 hours.
We've received your request and will be in touch within 24 hours.
