Properly Installing a Shower Base

The whole idea behind 1 piece shower stalls is no joints no leaks, right? Where there is water it will leak!
Once again we see that improper installation techniques cause a water leaking problem.
The less expensive shower bases are thinner and tend to flex when you move around on the shower floor and since the drain in these units is actually friction fit, so water can seep through and cause a problem.
The friction fit is actually a good idea because there will always be a different rate of movement between the shower base, the structural floor, and the drain piping. The drain pipe for the shower is usually a 1 ½” or 2” PVC pipe that slips through a rubber sleeve attached to the bottom of the shower base.
The problem in this case is that the floor of the shower unit actually flexes because of the lack of support from the bottom.
The proper method for installing the shower pan is to place it in a “bed” of mortar or similar acting product that will effectively cradle it and keep it from moving. My favorite product to do this is spray foam for a couple reasons. It creates the “bed” but it also deadens the sound and acts as an insulator so as not to conduct cold onto the base itself.
You must dry fit the shower base first to make sure everything lines up because once you set it in the foam you won’t get it back up.
To figure the thickness of the “bed” you need to lay the shower base upside down on carpet or some other soft surface as not to scratch it. Place a straight edge or level across the bottom and measure down to the floor of the unit. Add about ¾” to that measurement to get the thickness of the bed you need to put down.
When you have completed your dry fit you are ready to lay your “bed” down and place your base down. Simply spray the foam down on the floor and when it is built up to the desired height and coverage (generally 50% of the total area) place the base into it. Press firmly, but do not step into it or push down aggressively or you could cause a gap to form. Leave it sit for the recommended drying time on the “bed” product you have used and you are good to go.

OK Fine John but mine is already installed what can I do now to keep it from leaking??

Remove the drain gate, usually snaps in and out. Clean the area around the joint between the fiberglass base and the rubber gasket. You may need to use a putty knife. Then wipe it clean with nail polish remover, or other degreaser type of cleaner. Be careful it will not discolor fiberglass or PVC.
Now using a flashlight look into the drain not too far down you will see the actual drain pipe itself and looking carefully you can see the rubber sleeve just to the outside of it. Clean the top edge of the pipe and the sleeve right above it very good.
Using some 100% silicone, I recommend GE brand, run a bead around the top edge of the pipe onto the sleeve and another bead on the top where the gasket meets the base. Moisten your finger with a little water and smooth out the bead, not too much, just make sure it is sealed all the way around.
Let it dry for the recommended time and snap the drain in and you are good to go.