Expert Answers: Fix Moldy Grout

Have mold growing in the grout around your tub or shower and need to remove it pronto? HANDY has the answer.

Q: My sister had a new tub surround installed and she is having a major problem keeping the grout around it clean. Apparently it is quickly getting moldy. Recommendations? - Betty Galloway, Via Facebook

A: Many factors can cause mold to develop, especially in a humid environment such as a bath. The mold’s recurrence indicates that the moisture/mold source may be coming from inside the shower wall rather than from splashed water. If the mold is most concentrated near the faucet or plumbing lines, it might be due to a leaky connection inside the wall. Has your sister contacted the installer to see whether the surround is under warranty or to seek advice?

Because we don’t know what type of material the surround is, let’s clarify a couple of terms. Grout is a hardened porous material typically used to fill the spaces between stone or ceramic tiles. If the problem is with grout, it may not have been sealed (ideally after it was cured but before the shower was used). In that case, try to clean the grout with a mixture of one part hydrogen peroxide to two parts water. (Don’t use chlorine bleach; it can make white grout turn yellow.) Once you’re certain that the mold has been eliminated, allow the grout to dry for several days (checking that mold stains do not redevelop) and then apply grout sealer according to the manufacturer’s instructions. A second application of sealer — and periodic reapplications — may be needed.

If the surround is a solid-surface material or an acrylic or fiberglass panel, it should have been sealed along seams and edges using a silicone (or part-silicone) caulk sealant — not grout. Most kitchen-and-bath caulks are made with an antimicrobial ingredient to discourage mold growth. If mold is embedded in the caulk (not just on the surface), the caulk needs to be removed and the area thoroughly cleaned and dried before a new, mold-resistant sealant is applied (see photo). Again, it’s important to ensure that there is no source of water intrusion from behind the wall surface. Use of a proper-size bath vent is also essential in curbing humidity and preventing mold. - HANDY