[Expert advice] Which sealant to choose for a bathroom?

A sealant for a bathroom has to meet several specific requirements. First, it must resist mold growth. Second, it must be water-resistant. Third, it must be elastic, because the joints that need sealing in a bathroom are often subject to movement. On top of that, a bathroom sealant needs good adhesion to a range of materials.

To find a suitable sealant, look at the sealant selection chart. It shows that two types meet all of these requirements: hybrid and silicone sealants.

Hybrid sealants are a versatile, balanced solution: they combine the best of polyurethane, silicone, acrylic and rubber sealants and adhesives. Their main advantages are that they can be applied to a damp surface, have high strength and good adhesion, do not yellow, give off no odor and, most important, resist mold and mildew well. The flip side of that strong adhesion and high strength is that a hybrid sealant is harder to remove if it ever has to come off.

Silicone sealants are either acetoxy cure or neutral cure, depending on the curing system. Acetoxy sealants give off a sharp smell of acetic acid while they are being applied; neutral cure sealants are practically odorless. Acetoxy sealants are used on stainless steel, glass, ceramics and wood, but they are not compatible with alkaline materials (cement, lime, gypsum), marble or granite, and they corrode metals. Neutral cure sealants can be used without such restrictions.

By intended use, silicone sealants fall into general purpose, sanitary and specialty products. Sanitary sealants are the best choice for a bathroom, because they contain the most fungicide to prevent mold and mildew. General purpose and most specialty sealants can be used in a bathroom too — they also contain fungicide, although in smaller amounts. The exception is aquarium sealant: it resists mold and mildew poorly precisely because it contains no fungicide, which is harmful to aquarium fish and plants.