Shower Pan CPE Membranes
When you purchase your shower pan membrane you will need to be careful. The different liner products on the market all appear to be somewhat similar. You will find the CPE membranes at top quality plumbing wholesale houses that sell to plumbers and often at ceramic tile specialty stores.
The brand name CPE membrane I have had the best luck with is called Chloraloy. Visit a plumbing supply house or a real ceramic tile store and ask for a small sample. Note how supple and soft it is. The real McCoy - if you locate it - will have the words CHLORALOY 240 CPE written on it in numerous places. It will also state that it is 40 mils thick.
Once you get your hands on some Chloraloy, note how easy it is to bend the material. This will be important when you start to form inside corners. You will appreciate this flexibility as the material needs to fold back over on itself at each inside corner.
Certain situations require you to cut the membrane. For example, you will want to extend the CPE over your shower curb. When you cut the material you often will have to cut a patch or a small piece to wrap over/around the cut area. Be sure to purchase the special welding solvent made by the folks that make the Chloraloy. Don't try to use some other glue or adhesive. It won't work! The special solvent actually welds the pieces or patches together into one solid piece of CPE.
Pay attention when cutting out the round hole that allows the membrane to fit into the clamping drain assembly. If you cut the hole too big, you will have problems. Remember, you can always trim a little more off! Be conservative on your first attempt. Once you are sure of the fit, use an adhesive caulk on both sides of the membrane where it contacts the drain assembly. This acts sort of like pipe dope. Do NOT apply so much that it clogs the drain/weep holes around the top of the clamping ring. Pay attention to this detail - to be sure!