Undermount sinks and adhesives

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Forum topic by Pyro posted 03-21-2019 01:05 AM 164 views 0 times favorited 3 replies Add to Favorites Watch
View Pyro's profile


58 posts in 489 days

03-21-2019 01:05 AM

Hey guys,

Not sure this is totally appropriate for this forum but I can’t think of a better group of people to ask.

Sometimes when I’m working on undermount sinks it seems that they used a pretty serious clear sealant to adhere the flange of the sink to the underside of the counter top. I’ve found similar stuff on the bottom of toilets and figured someone probably used it to prevent movement when they couldn’t get the bolts to grab. It’s clear and it retains a certain degree of flexibility. I’m usually able to pull it off as a single strip from sinks with some good tugging or scrape it off a floor with a sharp enough tool.

I’m guessing this stuff is probably a polyurethane liquid nails or something? I’ve only ever used silicone when installing undermount sinks (along with clips to hold the actual sink of course). The reason I’m curious about this stuff is because when I find it on sinks it shows very little signs of wear, has kept the area sealed very well, and doesn’t seem to mold at all. I’m usually replacing the most expensive silicone I can get my hands on yearly in areas that see decent use.

Interested to know if I could start using this stuff on surfaces that aren’t too temperamental like a stainless sink? Anyone have experience? Appreciate your help as always.

3 replies so far

View HackFabrication's profile


99 posts in 39 days

#1 posted 03-21-2019 02:16 AM

When I had the granite counter tops installed at my house. the installers used scraps of wood and 2 part epoxy to secure the undermount SS sink to the rock. They put a length of 2×4 across the opening, and used a couple of quick clamps stuck through the drain openings to pull the sink tight to the rock. Seemed Hack to me, but in almost 10 years, I’ve never had an issue with it loosening up. They then ran a bead of clear silicone between the rock and the sink to prevent any leakage. You can’t see the silicone because how the sink mounts a bit larger than the opening in the rock.

-- "In the end, it's all Hack..."

View SMP's profile


595 posts in 233 days

#2 posted 03-21-2019 05:43 AM

Hmm normally i see clips and silicone, especially silicone on toilets. I was thinking pl400 but then you said clear. Which made me think maybe those hot urethane glue guns?

View Snipes's profile


392 posts in 2572 days

#3 posted 03-21-2019 11:51 AM

Most installers I see use silicone. I use clear quad polyurethane caulk alot

-- if it is to be it is up to me

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