Mildewed Bathroom Caulking

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Dear NH,
Where can I purchase polyurethane caulk? It is to be used in a shower stall. I have been using silicone but I have been experiencing mold problems. I understand that this does not occur when polyurethane is used.
PW from Schaumburg, IL

Dear PW,
Polyurethane caulk is available in many home and hardware stores. However, I don't believe that there is a polyurethane caulk available specifically for bathroom use... yet. In my experience, even manufacturers who produce polyurethane do not recommend using it in bath enclosures. Part of the reason may be that polyurethane is not as mildew resistant as the best "mildew-proof" acrylic latex caulks, manufactured by companies such as MD (Macklanburg-Duncan) and Polyseamseal.

It is a given that polyurethane is superior in both adhesive ability and flexibility (or "stretchiness") than either latex or silicone caulks. This is great in some applications, especially exterior joints where there is significant seasonal expansion and contraction. It is not generally necessary in bath enclosures. The stress on the joints in bath applications is just not that great, so the additional adhesive strength is essentially overkill! Since ALL bathroom caulks eventually become mildewed or simply loosen, the extra adhesive strength may even work against you come repair time!

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As far as mildew resistance goes, I would choose acrylic latex caulk over silicone caulk any day, especially the "mildew proof" varieties mentioned earlier. This is from personal experience with miles of mildewed caulk!


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