Kitchen sink caulking "flaking" off, looks like sand in some parts

Question

I'm trying to get help diagnosing what the issue is. I am re-caulking the area around my kitchen sink. Since the sink is a top mount, and the piece of countertop on the side is severely damaged, I thought I'd just use caulk to basically fill up completely and create a flush surface with the top edge. In other words, a REALLY thick layer.

To prepare adequately for this, I removed the old caulk, cleaned, and let it dry fully over 24 hours. Then I put on a thick layer, dried it for 24 hours. Then I put on a thinner finishing layer to smooth it out, and again let it dry for 24 hours. (While I know it's not ideal to do caulk over caulk, I also know it should work if the old caulk is still in good condition; and in this case, it was fresh!)

I started using it today, and noticed it's flaking away. See photo. On the caulk only piece, you'll see where it looks kind of sandy, and then also you'll notice even the thin finish layer that was applied directly to the sink (that was clean/dry) is flaking off.

Trying to figure out what possibly the reason was. Was it... 1) too thick and needed way longer than 24 hours to dry, 2) wrong product? (resident manager gave me a product that is labeled for doors, windows, molding, etc., but said it's fine to use. it's latex plus silicon, doesn't feel very rubbery like caulk I'm more used to, felt almost chalky like... spackle?), 3) other reason entirely?

ThankS!

Answer 1

The caulk is pulling up where it shrunk and was unable to bond to that area. try removing the caulk, and filling the gap with waterproof putty, which wont shrink as it dries. Let it cure, Then use a White Shellac-Based Interior/Spot Exterior Primer to seal the patched countertop before re-caulking. It generally dries in a half hour or so.

Answer 2

Since you mention "residence manager", I'll assume this is a rental of some sort and they've authorized you to do this work instead of fixing it themselves. I would contact the manager again and have him actually take a look at the damage. She may have heard "need to recaulk the sink" and figured the caulk was peeling up and may not quite understand the depth of the issue. If he takes a look at the "depth" of the problem, she may realize that this needs something more than just a fresh layer of caulk.

If, however, he wants you to just plug the hole with caulk, well, then, it's her property, just make sure you don't put anything below the sink that you want to stay dry, and bodge on...

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A thick layer of caulk isn't a good idea as a filler for rotting wood for any purpose.

If you're going to fill the gap with the caulk, build up your final thickness with thin applications of caulk, allowing each one to fully cure before applying the next layer.

The tube may say something like "waterproof in 2 hours" or "paintable in 4 hours", but in small print it'll say something like "fully cured in 24 hours". Like it or not, it's that 24 hours that you're going to have to wait.

Caulk will shrink a bit as it dries and your thick layer will shrink a lot if/when it ever gets fully cured in the middle.

Also, for a sink surround, a pure silicone tub/tile/shower type of caulk would probably be a better bet than an acrylic latex caulk.