Ceramic tile showers simply leak. Lots of people think that a ceramic tile shower that is in fantastic structural shape - meaning no cracks in the grout - are virtually waterproof. Nothing could be further from the truth. Beneath the tile is a bed of cement mortar that sits inside a waterproof membrane. Years ago the membranes were thin sheets of lead. Plumbers with great skills would seam the lead using a soldering iron and stick lead. Talk about craftsmanship! In fact, they would test for leaks by filling the pans with water.

Times Change

The days of making lead pans is all but gone. You still might be able to find an older plumber who can do it. It is actually OK that we don't use lead. The lead shower pans would fail over time. Chemicals in the water would set up a low voltage battery that would actually corrode the pan.

The plastics industry saved us from this problem with the introduction of chlorinated polyethylene (CPE). This flexible rubber like material is impervious to water and resists virtually any chemicals you can find within a typical residential home. It is also easy to work with!

Let's Get To Work

If you plan to install a shower pan liner yourself, it isn't too hard. It can be made infinitely easier if you can adjust the rough framing slightly. A trick I learned long ago is NOT to frame the shower wall corners tightly. I used to leave a 1/4 inch space at each corner. This means the total wall length is 1/2 inch shorter than the opening. This gap is a perfect place to store the extra CPE membrane material that bunches up as you round the corner. I would fold this material back on itself and nail it to the backside of one of the corner studs. If you don't do this, you end up with a hump of CPE liner in each corner. This excess material WILL cause your cement board wall material to angle out at the bottom.

Lap it Up!

The CPE membrane needs to lap up the sides of the shower basin walls at least 9 inches. A 12 inch lap is not unreasonable if you can afford to do it. The CPE material I would use comes in 4 and 5 foot widths. This allows you to accomplish a lap height fairly easily in standard sized showers.

Nail Heads

All nail heads in the subfloor need to be recessed. A nail head sticking above the floor might - over time - punch a hole in the membrane! Check for large splinters at the same time. I actually vacuum the area before installing the liner to remove any grit that could cause a problem.

Rout a Channel

The plastic plumbing drain you will invariably use has a 1/8 to 3/16ths inch thick flange lip on it. If you simply cut a hole for the drain assembly the flange will project above the top of the subfloor. This is bad news in my opinion. This means that water captured by the liner needs to climb over this lip to enter the weep holes. We all know water doesn't travel uphill (I know all about capillary attraction...doesn't work here!)

The solution is to rout a mortise or channel that allows the top of the drain flange to be flush with the subfloor. If you have a router handy it takes longer to get it out of the case than it does to actually use it to cut the mortise. This often overlooked detail, if forgotten, can cause a problem in some cases.

The Weep Holes

The plastic clamping ring drain has small weep holes. Look at it closely and you will see them. These holes are vitally important. If they get clogged with cement from the mud base, you are toast. Small washed gravel placed over the holes prevents clogs. When you cut the CPE membrane, make sure it does not interfere with the weep holes in any way. After the membrane and drain are tied together you should be able to see clearly through the holes down into the drain basin.

The Cement Base

The first cement mud bases I poured were goofed up. I made the cement/sand mixture too thin. You want your cement mud to be stiff, just like sand you use at the beach to make sand castles. The mixture will have plenty of moisture so that the cement will harden, trust me!

You must install the cement wall board in the shower area over the top of the CPE membrane. Hold the cement board up about 1 inch from the bottom of the membrane. With the cement board in place you can trace a level line on the cement board. This will help you place the cement mud perfectly. You only need about 1/8 inch per foot fall in the cement mud base. Be sure the cement base has no humps or dips or else laying the floor tile will be a nightmare!