Shower pan installation

I'm ready to install a new fiberglass shower pan into my bathroom remodel. In reading the instructions for the base it shows where to put the blocking and then says to drill holes throw the base and put screws through into the wall studs. There is no mention of using thinset or anything like that under the base.

Should I just follow the instructions? The floor is already level.

Good question and I'm in the exact same quandary. There is lots of chatter on this subject on the various forums. The otherwise very clear Black and Decker plumbing book shows pouring a layer of thinset before placing the receptor but warns against putting mortar where the receptor feet contact the floor. The pan illustrated is exactly the same as mine (Kohler/Sterling) and has numerous feet on about 6 in centers. How could you contrive to put the mortar everywhere but under the feet? (The directions do say to put a 1 in layer of mortar down, as an option.)

I will need to shim to level the receptor/pan and I do see that when I do this the pan will rest on the shims with some of the feet a bit shy of the floor. So maybe mortar/thinset makes sense, but only if it spreads and sets under the raised feet. I really don't understand this and I hope someone responds to our posting soon!

I used mortar placed in multiple piles about 6" diameter & 3" high under the base. This leaves room for it to "squish" when setting the pan. Doing this results in the pan feeling rock solid with no flex.

So would one think that isn't in the instructions as it's just assumed there should be some thinset below it. Once it "squished down" was it pretty flush with the floor then?

Did you need to shim, or does the mortar level the pan by itself? This is the part I can't visualize and it seems like an irreversible step.

Well I'm no expert myself but the mortor will level the pan for you you just need to press done on the spots that would be high and use a level the whole time.

I have never seen any tub manufacturer recommend using thinset.

Kohler/Sterling recommends mortar.

Yes, of course -- I should have said mortar, as recommended. Still, if you look elsewhere in the forum-sphere (not here, necessarily) you will find people using/recommending thinset, even drywall compound. This one is usually denounced by the next poster. The original poster suggests that the mortar bed will allow the pan to level just as it does when used for laying block, tapping/pushing down on the high spots.

If the plan is to use the mortar to level the shower pan then it should be done differently.

I'd use a sticky thin-set like Laticrete 254 as a slurry coat combing in 1/4" trowel marks on the plywood. Then some mortar mix nice and fluffy over top. Then a little 254 scratched onto the back side of the shower pan and then set into the mortar mix.

Be careful to get full coverage. Before installing any thin-set to the back of the shower pan you might dry fit it and then pull it up to see what kind of coverage your getting.

All the confusion and work to get this right is exactly why we just build them from scratch.

Don't forget to flood test your shower pan out to check your connection point. JW

You can tell that John has never set a Vickrel pan before. The bottom is a deep "waffle" pattern reinforcing structure with many legs coming down to contact the subfloor. It would not be feasible to trowel anything on the bottom of the pan.

Throw down some piles of mortar. Some people like to lay a "saran-wrap" thin layer of plastic between the mud and the base to keep it from sticking, just in case they need to pull it up and start over. Keep the mix fairly dry as if it is too wet it will shrink excessively as it dries. Thousands of acrylic tubs and shower bases have been set using this method- it works.

Drywall compound would be a big mistake as it it ever got wet it would all crumble.

Thanks, that's very clear. But I still leave the shimming in place, right? And I'm assuming you mean regular mortar, as in a wall.