Shower Pan Design [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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09-02-2017, 07:32 PM
I'm remodeling a tile shower and there's a crawl space beneath it. I've already removed the floor tile, old liner and OSB subfloor. The shower was 8 years old. I'm trying to decide whether to use OSB, plywood, hardiboard, cement board or backer board for the tile subfloor. Any suggestions from the pros on which is best?

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09-02-2017, 07:50 PM
Given a choice, I'd make that subfloor tongue & groove plywood. Second choice would OSB.

The other things you mention cannot be used as subfloor, but rather are intended to be underlayment on top of subfloor.

If you give us a little more info on scope of your project and perhaps some photos, we can advise mo' betta.

09-04-2017, 06:49 AM
Back in 2003 I built a shower on a concrete slab using this Forum and a signed copy of John Bridge's It turned out great. I've moved and now I live in a house with a plywood subfloor and crawl space beneath it. I'm planning to install a tiled walk-in shower. I've noticed around here that the builders always put the liner directly onto the wood subfloor. Then, they build a mortar bed with slope and tile on top of that. Is that an acceptable way to build the shower pan?

09-04-2017, 07:24 AM
Acceptable? No.

Is it done? Only by those who don't understand how a conventional liner and weeping drain works.

09-04-2017, 10:47 AM
Jim, there needs to be a preslope under the liner, that way the liner has slope towards the weep holes in the drain. Without the preslope, the water that soaks thru the tile and mud can't get to the drain and the water becomes stagnant.

On a plywood floor, set the drain up off the floor so the bottom flange is 3/4 from the plywood. On some drains, when the nubs on the bottom of the drain are resting on the plywood, the flange is about right, around 3/4 off the floor. Then add felt paper or poly to the plywood, then lath. Then the preslope can be installed so it's flush with the bottom flange. Next would be the liner.

Edit; But before the liner goes in, it's a good idea to notch the studs so the liner folds won't bulge the CBU out and also add blocking between the studs to support the liner.

09-04-2017, 11:10 AM
You guys are a huge help! Going with the plywood like Carbidetooth recommended.

Davy, If I build the preslope mud bed flush with the bottom flange, it doesn't seem like there would be a lot of room for more mud, thinset and tile. Do I tile directly to the liner?

Also, what's the thinnest I can make the preslope bed?

09-04-2017, 11:26 AM
I assume you have a standard 3 piece clamping drain that has 4 bolts holding it together. First, take it apart and see if it will clean up. Sometimes the bolts are rusty and in bad shape. You want to make sure the bolts tighten well and everything is cleaned up. Many times the drain has to be replaced.

The minimum is 3/4 at the drain, of course with the pitch, it'll get thicker towards the perimeter. The top mud bed will go on top of the liner and against the top section of the drain, that has the grate on it.

Check out the "shower construction info" in the liberry. Lots of info there.

09-09-2017, 11:27 AM
What keeps the drain clamp bolts from rusting over time since they sit in an area that routinely gets wet?

09-09-2017, 11:45 AM
Most of them used these days are stainless steel bolts and they won't rust. I have tore out showers that did have rusty bolts though so we never know exactly what you have. Those are usually in the old drains. The old metal drains nearly always have to be replaced because the bolts won't move at all. But with an 8 year old shower, it's probably plastic and might clean up. Just make sure it's in good shape before moving forward.

09-09-2017, 02:36 PM
Thanks for the quick replies. Seems like cutting a hole in the wood sub floor for the drain would weaken the pre-slope. Do you do anything extra to secure the drain?

09-09-2017, 03:23 PM
Welcome, Jim. :)

Yes, the hole in the subfloor will weaken it in that area, but a fella needs his drain to go somewhere, eh? Just another good reason to have a double layer subfloor where tile is to be installed.

If you cut the hole such that it's large enough for the drain riser but small enough for the drain to sit on or above the "feet" created by the bottom of the bolt receptors, you may be high enough for your mud floor. Or support the drain on the plumbing and the mud under it will provide additional support once finished.

My opinion; worth price charged.

09-09-2017, 04:06 PM
What Cx said. I have found that on most drains when the nubs on the bottom are resting on the plywood, it leaves the bottom flange about 3/4 off the plywood, just right for the felt paper, lath and preslope.

09-09-2017, 06:38 PM

Thanks for the advice. It's been 14 years since I did my last shower and the two of you were the primary guys that helped me back then. I've forgotten a lot since then. I bought some backer board from one of the moderators back then when I lived near Manassas, VA. Thought it was Davy but might have been someone else.

Do you recommend fastening the subfloor to the joists with screws or nails? Seems like screws would pull it tighter and ensure it was more solid. I'm using 3/4" plywood on 12" joists.


09-09-2017, 08:13 PM
Jim, I like to screw the floor down well just to make sure it's good and tight.

I try not to buy much backer board and can't ever remember selling it to anyone so I doubt it was me. :)

09-09-2017, 08:40 PM
And Davy wouldn't have lived in Virginia back then, either, Jim. We did have a moderator name of RobZ with us then and he lived in Virginia up near Crazyton, DC.

Like Davy, I prefer screws for all parts of a subfloor structure whenever possible.

10-01-2017, 01:11 PM
I re-did all the PVC piping under the floor of my shower and my bottom flange ended up not being perfectly perfectly level in one direction. Is that going to cause any major issues? It's a lot of re-work to redo and I'm not sure I'll get it level even if I redo it.

10-01-2017, 07:11 PM
Depends upon just how short of perfect it is, Jim.