geesh, I have to worry about that???!!!

I think that vacation homes in hilton head are probably very humid, leading to more mildew issues.

Thank you, beuhl! Your clear information has solidified my decision to purchase an undermount sink.
Maintenance is what may very well be the cause for the problems she mentioned.

There is such a thing a mildew-resistant caulk, make sure they use that.

morton, Thank you! I will surely do that! You are all just fantastic!

Wow! Another one of those little details that I would have had no clue on how to answer when my countertops arrive! Thank you Buehl and Morton 5!!!

I think your sister is confused. I live in what has to be the mold and mildew capital of the world and my sink is one place it hasn't thought to grow. I can't imagine what kind of a slob someone would have to be for their sink to get gross enough for mold or mildew to grow there.

Get your undermount sink and don't worry about this particular issue for another second.

Maybe the issue is that these are vacation homes in Hilton Head so there is a sufficient amount of time between people using the sink and maybe renters aren't as neat? I too had heard that it could be an issue, yet when I talked to friends who had undermount sinks I couldn't find anyone who had actually had problems with mold. We ended up with a farm sink but I wouldn't hesitate to get an undermount sink! The corners of my farm sink would get yucky if I didn't wipe them out from time to time as well, so I think people are spot on when they say you'd have to ignore wiping down your sink for quite awhile before you'd have any major issues.

Kat :)

I realize these comments were from several years ago but I too have this issue and, I am not a slob and I live in Massachusetts where heat and humidity are limited to a couple months a year. However, I will begin to use a toothbrush to clean this area regularly. Although the mold has become visible it is very hard to reach. I never have known anyone to need a toothbrush to clean where the sink and counter-top meet but I am going to begin using a toothbrush regularly to reach this area. I would think twice before getting another under-mount sink. The black mold that builds up is disgusting and almost impossible to reach. I am going to replace the molding today with the mold resistant caulking someone mentioned in this thread and see what happens.

I have been considering the possible issue of mold on an undermount sink, which is how I got to this informative site. I wonder if I can have my stone fabricator polish the underside, for a couple of inches around the sink, before installing it. Would this make it less susceptible to molding?

" I wonder if I can have my stone fabricator polish the underside, for a couple of inches around the sink, before installing it. Would this make it less susceptible to molding?"

Yes, and that's not a bad idea. No one has probably ever asked your fabricator to do this, so let him know you're willing to pay. I think up to $200.00 is reasonable. He should profile and polish.

Or just get a positive reveal, have no crud ledge, and pay no extra.

Are you kidding me, every undermount sink gets mold. I'm going back to the solid sink counter top. After 4 houses I'm done with undermounts.

A properly installed and maintained undermount sink does not get mold. Impossible.

Every undermount I have ever seen has mildewed, dirty caulking, i.e. it's no longer clear but black. Once it's turned black, it needs to be replaced. I don't know if it's improper maintenance or simply the wrong type of silicone caulking, but it can't be bleached or cleaned. Last year I bought an 11-year old house with a solid surface counter, & undermount stainless steel sink. I simply cannot get the caulk clean. We are planning a remodel and though I prefer the look of the undermount sinks, especially when used with granite, I am so disgusted by my experience I am having trouble finding a sink and may resort to a drop-in.

I will pay a $10,000.00 bounty on every undermount sink I've ever installed with a positive reveal that has any mold or mildew. Flush mount Karran's included. Not happening. Ever.

Please let us know your secret for preventing mold in an undermount sink with positive reveal.

If the sink is a double bowl, there is sink surface area revealed on the front and back and that is where the mold grows, even with constant cleaning and good quality silicone caulk (which resides slightly under the granite edge). I was concerned about this prior to purchase of ours because in my 38 years of caulking experience I have yet to find ANY caulk impervious to mold. Now that I have had an undermount with pos reveal for a couple of years, I am experiencing the mold issue.

We have always dried the neg reveal area between the bowls after every use to prevent the issue, but it has not worked.

jostra99:

Your sink needs to be remounted. I promise if it's done right you'll never have any mold issues. Your topical application of caulk is like a band-aid on a blown tire; the mold is not the caulk's fault. 100% silicone caulk needs to be applied between the sink flange and the stone bottom. The only way that can happen is by removing and reinstalling the sink. Here's how with pictures.