Published on January 13th, 2014 | by Henri


Recommended caulk for use in bathrooms

Q.  I would like your recommendation for a caulk for bathroom applications: shower enclosures, sinks, base of the toilet, etc. A few years ago, I used Phenoseal, because that is what a plumber used. I had previously used silicone caulk and found it difficult to apply cleanly.

The advantage of Phenoseal is that you can smooth it out with a damp finger (or similar shaped rod) to get a clean bead. If you make too much of a mess, you can clean it up with a wet sponge and start over. You can’t do that with silicone.

Now the downside: After a year or so, a slight amount of black mold started growing in the caulk, mainly in the shower enclosure (not surprising since it’s a wet environment). Note that I had bleached the area before applying the caulk, and I tried bleaching it when the mold first appeared. This helped some, but now 5 yrs later, the caulk in the shower enclosure is heavily overgrown with mold, and I need to replace it.

Should I still use Phenoseal, perhaps with an anti-mold additive? I assume that Phenoseal is susceptible to mold because it is a water-based (latex?) compound. Or should I switch back to a silicone caulk and practice, practice, practice laying down a clean bead?

A.    In my experience, silicone is the worst thing to use at the joint of a tub and tiles. I have seen so many failures in my nearly 60 years in the residential construction field. It will eventually peel and allow water to get behind it, leading to serious problems.

I have used polyurethane caulking for bathrooms for many years. But you need to allow the caulking seven days air-curing before you can get it wet or it will turn yellowish-pink. Even then, the white caulk will turn slightly greyer over time.

You can find polyurethane caulking in building supply houses that specialize in masonry and waterproofing products. A.H. Harris, with stores throughout the east coast, carries Sikaflex 1-a, my favorite and a product I have used for 50 plus years. Their website is

You may want to try Dap Kwik Seal Plus Premium Kitchen & Bath Adhesive Caulk with Microban. The manufacturer says that Microban fights mold and mildew and the growth of stains and odor-causing bacteria. Although it is a siliconized latex caulk, it has much better adhesion than pure silicone caulking. It is guaranteed crack-proof.

Unfortunately, although the caulk remained white, I have also experienced separation between tub and tiled walls in year-long tests on the same tub, half of which was caulked with it and half with Sikaflex-1a.

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