Top 5 Tips – Waterproofing for Tiled Showers

Tip #1 – Choose a liquid-applied waterproofing membrane
Unlike most waterproofing methods, a liquid-applied elastomeric membrane creates a seamless barrier that includes the drain assembly. The membrane provides thin, smooth, monolithic coverage over an area of any shape or size, in any configuration, and on horizontal, vertical or overhead surfaces. The liquid is simply troweled, rolled or sprayed onto the substrate and allowed to dry. If there’s space at changes of plane – no problem – a mesh tape will help you bridge the gap.

Some liquids, such as Custom’s RedGard Waterproofing and Crack Prevention Membrane, also provide crack isolation and exceed both ANSI A118.10 and A118.12 standards. RedGard qualifies as an IAPMO shower pan liner and meets many rigorous building and plumbing codes. As a low perm vapor barrier, RedGard is ideal for effectively managing moisture vapor in steam rooms and gang showers.

CUSTOM also offers a liquid solution with even faster curing – RedGard SpeedCoat Rapid-Curing Waterproofing Membrane. This special formula performs even in cold or damp conditions.

Tip #2 – Ensure proper drainage
Regardless of size, the shower floor and tile assembly must be properly pitched to direct runoff down the drain. The Tile Council of North America recommends sloping mortar beds in showers ¼ inch per foot to the drain. As illustrated in TCNA detail B421, the waterproofing membrane is applied on the surface of the mortar bed, not under it. This method prevents the mortar bed and substrate from becoming saturated with water. If the membrane is applied under the mortar bed, a cement-based pre-slope must be installed under the membrane.

Always tie the liquid membrane into the drain by applying it to the bottom of the drain flange and clamping it in place. Then, surround the drain with pea gravel or a weep protector to prevent mortar from blocking the weep holes. Position drain strainers so they are flush with the eventual tile surface, not above it. Drain assemblies themselves must be secured so they do not deflect and damage the membrane.

Tip #3 – Prepare all substrates carefully
In addition to the 1/4″ per foot floor pitch towards the drain, ensure that all horizontal surfaces, including seats and shelves, are sloped and smooth, with no low spots or bird baths that could collect water. Standing water in a shower can lead to stained natural stone, premature failures, efflorescence and the growth of mold and mildew.

Shower walls must be plumb, squared and treated with waterproofing membrane to the top of the area to be tiled. Do not use drywall or green board in showers or even tub surrounds.

Create a suitable substrate for tiled walls by using a water-proof cement backerboard such as WonderBoard Lite. Prior to applying the membrane, ensure that all wall and floor surfaces are clean, dry and structurally sound. Dust, residues and other contaminants can prevent the waterproofing membrane from achieving a proper bond.

Tip #4 – Follow the manufacturer’s instructions
Since the integrity of the waterproofing membrane is so critical, it is very important to follow the directions given by the manufacturer. Make sure that the membrane is applied at the specified coverage rate or thickness, without any pinholes or voids, and ensure a continuous film. Liquid membranes must be allowed to fully cure between coats. A fiberglass mesh tape should be embedded on the drain transition and may be needed for reinforcement at changes of plane and plumbing protrusions.

Protect the membrane following application so it is not punctured, soiled or damaged by other trades. Don’t neglect flood testing before installing the tile. If by any chance you need to repair an imperfection in the membrane, this will be infinitely easier and less expensive before the tile is set and grouted.

Tip #5 – Use a high performance installation system
Showers are challenging areas that call for high performance tile installation materials. This is especially true when shower walls are being set with large format porcelain, natural stone or thin, gauged porcelain tile. Given the size and weight of these materials and the wet conditions, a mortar meeting A118.15T should be used. When formulated for large format tile and stone, these thixotropic mortars, such as MegaLite and ProLite, will help hold heavy tile in place on walls without sagging.

When a cement-based grout is used in showers, it should be sealed after curing and resealed annually. Or, choose a grout that does not require sealing, such as Fusion Pro Single Component Grout. Fill soft movement joints, plumbing protrusions and changes of plane in the tile assembly with a flexible, mildew resistant sealant like Commercial 100% Silicone Sealant.