What Safe, Nontoxic Sealants are Best for Repairing a Fiberglass Shower and Tub?

Find out how to patch holes in a fiberglass shower and tub using nontoxic, safe sealants.

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Q: I have a fiberglass (I believe) shower and tub, both of which have several small holes in them. We purchased a tub and shower repair kit (gel coat patch), which we have not yet opened. It has several warnings (“keep out of reach of children,” “may cause severe burns,” etc.). Is there anything safer or less toxic we might use to repair our shower and tub? And what can we do to prevent these holes from forming in the first place? —Lisa Lewis, via e-mail 

A: It would help to know whether your tub is fiberglass or not, as fiberglass requires different repair materials and might have different reasons for wearing through. A lot of tubs are now acrylic, and these can be hard to distinguish from fiberglass. From a performance standpoint, acrylic (a hard form of plastic) is better than fiberglass because it lasts longer and doesn’t break down as much. Both fiberglass and acrylic are somewhat toxic to make and repair but have low toxic health impacts once in use (at least as bathtubs). To find out whether your tub is fiberglass or acrylic, research the company that made it. A contractor should also be able to tell you.

Let’s assume your tub is fiberglass because of the holes. Fiberglass uses a catalyst, typically a fiberglass resin, to set. These resins contain styrene, a toxic chemical that disrupts the nervous system. Most fiberglass repair kits also contain methyl ketone, with health effects similar to styrene. When these chemicals outgas during the setting process, you’re exposed to toxic health risks.

Is there a nontoxic way to repair fiberglass? In a bathtub, water pressure will affect the repaired area over time, so the seal you’re creating needs to hold. Unfortunately, a more environmentally benign solution, such as silicone, is not meant for bridging structural gaps.

What’s making the holes? It’s hard to know for sure. Holes can form in fiberglass either from regular friction on the surface or because water is settling directly beneath the glass, where water-borne bacteria can gather and locate nutrients that may be in contact with the fiberglass. When you take baths, the tub can create a bubble of wetness under the fiberglass layers. As this grows, so does the amount of bacterial and fungal decay. If this is the cause of the damage, further holes will form in your tub and repair is only a short-term solution.

If you do elect to patch your holes, make sure you have excellent ventilation. Get a fan or an organic vapor respirator, available from Green Home and other sites for about $75. If the holes are not in a pressure-critical area, consider a silicone-based sealant. OSI makes a good one.

Lawrence Axil Comras is president and CEO of Green Home, an online store that has been greening U.S. homes since 1999.