HOW TO INSTALL, INSTALLING A REDY TO TILE SHOWER PAN, BASE, TRAY OR RECEPTOR
I see posts all over the web about folks having problems with these pans. First off, they are a little flimsy. The pans flex really easy and if you are lucky enough to get one delivered that isnt damaged you will see you have to be careful since they are brittle and crack really easy. They are made of an expanded foam, not too different than a coffee cup, so while they should service you just fine once installed you need to be extra careful handling it.
Leveling the Pan: Setting the pan in the standard dry set mortar is what some of the manufacturers recommend. If you have a level floor that is best since it can be challenging to get these to level up. Over the years, many folks have asked me the best way to install a Tile Redi Shower pan and I have coached people from all over the country and its funny how there are regional customs with the names…some call them shower pans, shower bases, shower trays, shower receptors. It doesnt matter what you call it. We will get you squared away here.
Dryfit. Dryfit. Dryfit. Dont bull and jam and try to mortar it down and set a rigid shower pan pan all at once…unless you have done a few. Dryfit the pan in the enclosure to be sure that the hub for the drain is down into hole you cut for it which is usually about 4 1/2″ to 5″…too big weakens the floor around the drain and too tight can mean you have to force the hub down a little…dont do that. Setting a few shims or marking the studs with a pencil line will help you get the pan on the level.
Over Plywood: With this system you really need to have the second layer of plywood in place since the pans can flex around the drains. This is Tile Council of America standard industry practice for subfloor prep….. 1 1/8″ minimum APA grade plywood. Usually 1/2″ of mortar can work well but only if the floor is stiff. I dont understand why the manufacturer wont specify mortars, but be sure to set the pan in the mortar and then remove it to be sure all the ribs have touched down and are wet. Removing one of those Redy to Tile Shower Bases may take two people but it is worth it to be sure you have no dry spots. Touch up the mortar if necessary and re-set the pan and leave it be until it sets if you can. I prefer not to pound the pan down if I already know it is bedded. If pencil marks are put on the studs then you know you are down. You dont want to flex the pan down or weight it down in the middle. Generally the Ready to tile Shower Tray pans dont need fastening to the studs. If you get one that isnt straight you may need to pull the bow out of it with a few screws. I know people do it but it doesnt seem necessary, especially if you are using their flashing installation system. My personal bug is that the flashing costs about $50 extra for a few little pieces of aluminum that you can buy at HD for about $3.
Note: I have heard of instances when people use waxed or waterproof chip board or osb subfloors and set these directly on them and the mortar doesnt set up because the water is trapped between two layers of impermeable material. You need to use a vapor permeable layer on the second layer of subfloor. I have heard of folks using a urethane based construction adhesive or spray foam on the ribs if you can test for adhesion. Some of those expanding foams can force the pan to rise up or even distort out of shape because they are a little flimsy. If this happens you will have hollows under the pan which can be really bad.
On Concrete: I think the traditional dryset mortar method that some manufactiurers recommend will work fine but I also hear from folks who have used the original non modified thinset mortar because it is easier to work with and stays wet a little longer. None of the thinset mortars should be used to build up an out of level floor. On an out of level concrete floor it may be easier to just build up the floor with some dryset mortar and screed it off level and let it set before installing the pan. In any installation, having a level floor is the easiest way to assure a good install.