Waterproofing a Shower or Tub Surround

Why Waterproofing Is Critical

Tile and grout are not waterproof — they are water-resistant at best. Without a proper waterproof membrane behind the tiles, water slowly migrates through grout joints and reaches the wall substrate, causing mold growth, wood rot, and eventual structural failure. This damage is hidden behind the tile and often progresses significantly before any visible signs appear. Proper waterproofing during construction or renovation is far less expensive than remediation after water damage occurs.

Waterproofing Methods

The two main waterproofing approaches are sheet membranes and liquid-applied membranes. Sheet membranes (like Kerdi or GoBoard) are polyethylene or foam sheets bonded to the wall surface with thin-set mortar or adhesive. They provide consistent, reliable waterproofing and also serve as the tile substrate. Liquid-applied membranes (like RedGard or Hydroban) are painted or rolled onto cement board in two coats, creating a continuous waterproof barrier. Both methods are effective when properly installed.

Critical Areas

Pay special attention to the most vulnerable areas: the horizontal joint where the wall meets the tub or shower pan (use a pre-formed waterproof corner strip), all inside corners (apply extra membrane or sealant band), around the shower valve and shower head openings (use waterproof pipe collars or gaskets), and at the transition between the wet area and the rest of the bathroom. The shower pan or tub lip should overlap the wall membrane so water flows down the membrane and onto the pan surface rather than behind the pan.

Common Mistakes

The most common waterproofing mistake is using regular drywall or greenboard (moisture-resistant drywall) as the tile substrate in wet areas — neither is suitable. Use cement board (HardieBacker, Durock) or foam board (Kerdi-Board, GoBoard) in wet areas. Another mistake is failing to waterproof the entire wet zone — waterproof from the tub or pan to at least 6 inches above the shower head height, and the entire ceiling if it is a steam shower. Do not rely on grout as a waterproof barrier — grout cracks and deteriorates over time. Apply the waterproof membrane to the substrate before tiling, and maintain caulk joints (not grout) at all changes in plane.