Shower Pan Upgrade – Oldschool Mortar-bed meets Modern Thin-bed Membrane


A few weeks ago this bright bathroom had a serious problem… The shower pan was showing serious signs of water infiltration.  Tiles were loose on the curb of the shower, and the joints between radius tiles around the perimeter of the shower were soft and discolored.  Much of the grout had eroded from the joints between the field tiles and appeared to be depositing in the drain.  Due to the amount of buildup in the drain, it was clear this had been going on for quite some time.




It was obvious this problem was more than skin deep.  When I pressed on the loose tiles, water seeped from between the joints.  The mortar bed underneath was clearly saturated with water and would need to be replaced.   There was also the issue of that horrid drain… which would need to be replaced with a new drain assembly from Schluter Systems.  Schluter offers a shower pan system which is a combination of products specifically designed to drain water away from the setting bed and into the drain.  Older installation methods place a liner under the mortar pan, which is too low for the water to flow into the drain assembly.  Modern thin-bed membranes are installed directly under the tile and divert water into the drain before it can soak into the setting bed.  Schluter also offers a pre-sloped shower pan which is much easier to install than a traditional mortar bed, and is custom fit to the drain assembly.  I had Progressive Plumbing of Durham install the new drain section and flange, which was a breeze.  After a short explanation, Steve made quick work of installing the drain.  He even managed to find the base of the drain, in the garage, on his first try!  (I could have sworn it was in that chase).  After everything was installed I taped up the flange and opening to prevent debris from falling in.





With the drain installed, I was free to complete demolition.   The rest of the floor crumbled away with a few well placed strikes from my hammer.  I was in for a surprise when I reached the radius tiles on the walls and curb… The tiles in these areas were laid on top of a drywall product!  As water accumulated in the mortar bed, it merely wicked into the drywall.  Over time the bond between drywall and tile was broken, which let water enter the lower portion of the wall.  My guess as to why these lower sections were drywalled instead of using treated plywood or backer board is because of the thick folds in the Chloroloy liner.  Because typical Chloroloy liners can be 30-40 mil in thickness they are difficult to work into corners.  Folding the liners into inside corners created a buildup of material which can throw things out of alignment.  To avoid this, the original installer used drywall because it can be easily shaped to compensate for  “proud” areas in the corners.  To retrofit the new membrane system, I replaced the drywall patches at the bottom of the shower wall with treated plywood, which I built up to the proper thickness.  Once I had built the area out to the correct height and thickness, the boards were removed and wrapped in Shcluter Kerdi membrane.  I chose to use the wrapped plywood instead of cement backer board in this case, because it was easier to work  into shape with my table saw.  A continuous sheet of Kerdi membrane was then installed over the wrapped plywood, shower pan and drain.  After troweling out the sheet of membrane and installing the pre-formed corner pieces, I cut the hole for the drain.  It is easy to see that any water which manages to get beneath the tile will flow across the surface of the membrane and into the drain assembly.



Now that I have a watertight pan which has the proper sloped of 1/4 inch per foot, it is time to lay tile!   Because of a tight deadline, I needed to work long hours to complete this project on time.  To do this I needed to set my saw up inside the garage.   I pulled this off without a mess by using a couple of tricks.  First of all, I used good hearing protection!  I also took the time to set my saw up a little differently than usual.  I rented the saw from Triad Equipment and after a bit of tuning, I had it making perfect cuts.  I tore open one side of a trash bag and taped it to the saw so that any water slung from the blade would drip back into the tray below.  I also have a habit of placing the water pump in a bucket of fresh water instead of  in the pan beneath the saw.  This keeps it clean and clog-free!  Laying the tile went quickly.  I used polymer-modified thin-set to adhere both the membrane and the tile, and fortified non-sanded grout in the joints.  After cleaning up, I installed the new stainless steel Schluter drain cover which also serves as a sharp accent to the new tile.  With the door and glass replaced and the grout sealed, this shower is ready to rock for years to come.





Category(s): Project Archive

Leave a Reply

Your email address will not be published. Required fields are marked *