I was working on a tile shower recently where the homeowner had already purchased a PVC liner with clamping drain, which is the conventional system for waterproofing tile showers.  I DON’T USE THIS SYSTEM.   I use the Kerdi waterproofing system and I could go into many reasons why it’s the superior method, but that’s beside the point of this post.  I wanted to illustrate one reason why the PVC liner is inadequate- and it was even pictured on the packaging!

To have any chance of getting water down the drain, the PVC liner must be installed on a sloped surface.  This is not complicated.  Yet, even the liner’s packaging showed it installed over a level subfloor.  The problem with this is that once the water gets to the liner it is not motivated to move.  It just sits there, eventually causing mold and mildew from beneath your tile, or even leaks.

What’s worse is that most often I’ve seen these sytems installed with the drain sitting on top of the floor like this picture above from a leaking shower I took apart (read more here).  This means that not only is the floor level so the water won’t drain, but the drain is slightly above the floor surface and you will always have a pool of water sitting in the liner below your shower tile.

These issues are VERY COMMON.  It makes the shower more likely to leak and have mold issues where it seems like you can never get the grout clean because the stains are coming from below, etc.


With the Kerdi Waterproofing system, the membrane is installed over the sloped floor, directly under the tile.  It bonds to the wide flange on the drain.  There is nowhere for water to pool and any water that seeps through the grout will be motivated to reach the drain because of the sloped floor.  It’s also much easier to install than the two mortar beds required to get a PVC liner to actually work.

This photo (right) shows a shower that was previously leaking before I tore out the liner and installed the Kerdi system throughout.  After the membrane is applied to all the surfaces with unmodified thinset with corners overlapping by a couple inches, tile can be directly and immediatelly applied.