digest
Short Summary
Main recommendation: Waterproof a shower or tub wall with the Schluter Kerdi membrane, adhered using a non-modified cement (the presenter uses MAPEI Keraflex/Caribon), rather than relying on tile and grout as the waterproof layer. The presenter stresses that the cement type matters a great deal, since modified cements won't bond to the plastic membrane.
Key Points
- Tile and grout are not waterproof on their own; any tile placed over the membrane is only a water diversion layer for aesthetics, and the membrane can be removed and reinstalled later.
- The Kerdi membrane is a plastic, cloth-like sheet that modified (latex-polymer) cement will not adhere to, which is a common mistake.
- Modern showers face heavier use (rain showerheads, spa tubs, longer showers, more users), so older tile-over-drywall systems that rely on glue and no membrane now fail much faster—he says a shower that once lasted 20-30 years may now fail in about 5 years.
- The presenter cites a 10-year manufacturer's warranty for the membrane when installed to factory specifications, which he calls better than any other product on the market.
- Retailers may stock the membrane but not the correct cement, and staff may offer an incompatible substitute that will fail and fall off the wall.
Details Worth Noting
- Concrete instructions:
- Use a non-modified cement (traditional cement with no latex polymer), such as MAPEI Keraflex or Caribon, and confirm the store carries it before buying the membrane.
- Mix the cement, let it sit about 10 minutes, then do not add water again once it has set up (this is the same non-modified cement, not a different product).
- Aim for a loose, wetter consistency than a tile-setting mix, silky smooth and without granules, because the Schluter trowel grooves are small.
- Apply a generous first coat of cement to the wall, then trowel it out for even coverage, holding the trowel as you would for drywall mud.
- Press the membrane onto the wet cement like wallpaper, keeping corner joints tight, stretching it out, and working out air bubbles from the center outward.
- Where panels meet, use edge tape with a two-inch overlap for convenience, or overlap the sheet directly if you are experienced with the membrane.
- The presenter recommends taking the Schluter Kerdi course if you plan to do this professionally; he jokingly mentions he took it in Toronto over two days and got a card, hat, and T-shirt.
- Older tile surrounds on drywall without a membrane showed mold by 1983, illustrating the failure mode the membrane is meant to prevent.
- The Kerdi membrane is described as waterproof and vapor proof, which is why the wall can be left dry behind it.
Bottom Line
A Kerdi membrane installed with the correct non-modified cement is the key to a durable waterproof shower, and the tile on top matters far less than the membrane and adhesive beneath it.
