hannahcraig•10d agoTop Commenter

Polyurethane vs silicone sealant on a crown job, I picked wrong

Had a big crown repair last month on a 1920s house. Old clay flue liner, lots of cracks. I usually go with silicone for the flexibility but I got talked into a high-temp polyurethane by the supplier. Said it bonds better to old clay. First heavy rain three days later and I got a call about water dripping down the fireplace. Pulled the cap off and the polyurethane had already pulled away in two spots. Total failure. Cost me a return trip and a free replacement. Silicone would have held no problem. That poly stuff just doesn't like moisture during cure. Anyone else had polyurethane fail on older flues?

3 comments

3 Comments

wright.leo10d ago

Did you try blaming the weather gods or was it more of a "well, that's my day ruined" kinda moment? I've definitely been there before, thinking I was being smart and ending up looking like a total goof.

zara_sanchez10d agoMost Upvoted

Gotta back up what maxl93 said about that shrinkage issue. I had a buddy who used poly on a 1910 bungalow and it pulled away at the seams inside of a month. Old clay has this weird way of absorbing just enough moisture from the poly to mess with the cure, leaving it brittle. Silicone just handles the movement better, especially on those big old houses that settle and shift all the time. That rookie trap label fits, I've fallen for it once and won't again.

maxl9310d ago

Man polyurethane on old clay is a rookie trap if you ask me. That stuff shrinks when it cures and old clay is too porous for it to grab properly. Silicone handles the expansion and contraction way better on those old houses. Nobody at my shop uses poly for crowns anymore after we had the same kind of blowout. Live and learn I guess but dang that return trip stings.