What is a waterproofing membrane?

A waterproofing membrane is either a flexible sheet or a brushed-on liquid coating applied to walls, floors, and shower enclosures before tile installation. Products like Kerdi (a polyethylene sheet) and RedGard (a liquid-applied elastomer) act as a continuous barrier that stops water from seeping behind the tile into wood framing, drywall, and structural materials.

In Connecticut's climate, where humidity levels remain high year-round and seasonal moisture swings are common, a waterproofing membrane is essential for preventing rot, mold growth, and structural decay. Bathrooms are particularly vulnerable because they're exposed to constant spray, steam, and condensation. Even small grout cracks or gaps at corners allow water to migrate behind tile. Once water reaches the framing, remediation becomes expensive and invasive.

Waterproofing membranes are most critical in high-moisture zones including shower walls, shower pans, and tub surround areas. They're installed after framing and before substrate (cement board or backerboard) and tile go down. The membrane must be continuous and extend past corner joints and around penetrations like pipes and drains to be fully effective.

Proper application ensures that even if grout deteriorates or tile cracks over time, water remains contained within the tile assembly and drains harmlessly away. Remodelers installing walk-in showers and tub conversions typically prioritize membrane selection and installation because these fixtures see the most sustained water exposure.