Prepan questions [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-02-2019, 10:57 AM
I'm new to the forum and this the first shower I have attempted. I live in Massachusetts where the plumber installs the membrane. It will be a walk in shower with a sill, about 54 by 36. The house was built in 1953 with balloon framing. I would like to make the pan and do The rest of the work myself.
A problem is that the subfloor has a substantial slope sinking to the far wall with the plumbing rough, in the picture. About 2 inches over 4 feet. Of course, this slope is not towards the drain.
The plumber says that he always puts the membrane over the subfloor. Presumably then I would put the pan in, in one pour without a prepan. I am concerned that without a prepan any seepage will collect in the membrane at the low end and have no way out. It seems to me that a properly sloped prepan with a rubber membrane over it would channel seepage to the drain.
The plumber is a pretty adamant guy, but I will fight to do the job right-if a prepan is necessary.
The blocking between the studs isn't installed yet. I'll take the advice about notching the studs a foot up. Is a sawzall the best way to go?

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07-02-2019, 12:00 PM
your thoughts are correct.

add to that, if you are using a PVC membrane, your drain should NOT be flush with the floor. It should be like 1.5in elevated. The preslope takes up this thickness and can account for the dip in the floor.

I'd find another guy asap before any more work is done...

when you say notch the studs, I presume you are not going to just hack them up with a sawzall?? Below is what you want.

07-02-2019, 12:33 PM
Thanks for the advice. Your link for the notching seems to be broken. Any other thoughts about notching?
When you say that the drain should be an inch and a half higher than the floor, you aren't referring to the flange, but the drain itself-right? The drain is already 1.5 to 2 inches higher than the low area.

07-02-2019, 01:00 PM

here is the link for notching. there is a good pic there.

with respect to the floor drain, yes, it should be floating above the floor. look at this video:

07-02-2019, 01:35 PM
I got the link and I saw the notching diagram, but did not see any suggestions on how to notch. I'm open to ideas. I also have some 1/4 luan . I wonder if it would be easier to shim above than notch below.
Your comment about the shower drain saved me lots of grief.

07-02-2019, 01:43 PM
You can notch the lower 6in, or shim everything above it. Same thing. I think some guys use a hand chisel, others a router, some an oscillating tool. Im sure you COULD use a sawzall, but I just pictured you going in there and cuttin'g the lower 6in off each stud!

if the low spot is a good 1.5 to 2in, Why not fill it in with some SLC ?Or pack more mud there for the preslope....

07-02-2019, 01:54 PM
I'm planning on using more mud to get a level edge all around with a 1/4 inch slope to the drain per foot.
Hadn't thought of a router. A chance to buy a new tool....

07-02-2019, 03:19 PM
Welcome, Dave. :)

What you need at that drain is to have no less than 3/4" thickness of your deck mud between the floor and the top of the bottom flange. And a level perimeter as you've suggested with a minimum slope of 1/4" per foot to the farthest corner of the shower. You absolutely must have the pre-slope under your liner and any responsible plumber should know that. Emphasis on responsible and should.

As for notching the bottom of the studs for your pan liner, while I have a handful of routers and like them very much, I can't see any reasonable way to use one to do that notching. Perhaps Mike will educate me. The Sawzall will work, although my first choice would be a wood chisel. It doesn't take much. And you need to recess the stud bottoms of the studs to the height of your pan liner, which must be at least 3" above the top of your shower curb.

My opinion; worth price charged.

07-02-2019, 06:18 PM
Thanks for the super helpful advice. Is 3/4 inch the minimum depth for the mortar anywhere in the prepan?
I was going to mix my mortar with sand and Portland cement. Do you advise latex additive?

07-02-2019, 07:27 PM
Dave, usually the thinnest part of the preslope is at the drain but that may not be the case in your shower. You want it 3/4 at the thinnest part, where ever that might be. I have no idea how thick it will be at your drain.

I usually cut the hole in the plywood around 2 1/2 inches in diameter, that allows the 4 nubs on the bottom of the drain to rest on the plywood. Doing that usually gives me about 3/4 mud around the drain. The flange shouldn't be resting on the floor.

You'll want tar paper (or poly) on the plywood and lath stapled down before the preslope goes down.

I've used a Sawsall a time or two for notching the studs but it's easy to get it deeper than it needs to be. A sharp wood chisel works well like Cx mentioned.

Just trying to lower the chance of being confused, the membrane is actually the "pan", not the cement mud bed.

5 to 1 mix of mud made good and damp without latex works fine.

07-03-2019, 07:03 AM
A hand-held plunge router can clean out a pocket and set the depth evenly and precisely. You then clean it up with a hammer/chisel. I know, it doesnt need to be precise, but I was throwing out options. No idea what tools this guy has or has used. You could use a butter knife and a rock too. Should I provide instructions for that?

:stick:Come on CX.....

Tiger Mountain Tile Inc
07-03-2019, 10:14 AM
For the studs, I use a planer whenever possible but obviously it won't get in the corners so the old technology of a chisel still works for that.

But I will butt strip the shower first to get the walls flat. Then that will tell me if I even need to notch the bottom of the studs. If you have a couple of shims on the wall then there's no need to notch.

07-03-2019, 11:21 AM
I've used a plunge router to notch studs. I set the plunge depth to the depth I want and it precisely notches the studs to that depth. Once I move down enough that the guide plate on the router is no longer supported on one side (due to the notching) I hold a strip of wood with my left hand under the router to support the router plate so that the plunge thickness is kept consistent all the way down. This way is fast and precise but noisy and messy compared to a chisel and hammer. I prefer this over a planer because I feel it's much easier to notch precisely and a planer makes just as much noise and mess.

When it comes to a corner I can still use the router because I use a routing bit long enough to cover the width of a stud. In this case I draw a guide line for my notch and hold the router to the side of the stud. Not quite as precise but still gets the job done.

07-03-2019, 11:23 AM
Another option that I have used is to use a wood drill bit at least an inch or so and drill out the largest portion of the studs. From there, it's easy to dress out the remains with a chisel....:idea:

07-03-2019, 09:06 PM
Hi Dave,
I like to scribe a line around my flange set my jigsaw to 45 degrees and cut out the plywood. This makes sure the flange fits completely flush with the sub floor.
I take a couple of 12" pieces of 2x4 and screw to the underside of the floor 4" apart. This assures the flange is supported, use 2 or 3 roofing nails to hold the flange firm. The distance from drain to farthest wall determines slope, typical would 2 to 3 feet would equal a 3/4" screed. nail this screed down all the way around the perimeter of the shower. I always have Ardex or Plani patch on my truck. its quick drying and solid. Make your preslope. Planing and chiseling is a fair amount of work, especially at the corners where you have multiple layers.
Get yourself some Lathe strips, a bundle is cheap and there uniform. 2 tacks will hold it in place and your ready to go,

That's how I do It.
Happy 4th

07-11-2019, 07:12 PM
I have just put in my prepan using Quikrete sandmix with an added bag of sand per bag of sandmix. The prepan looks great and the next step will be to install the rubber membrane and then a final layer of mud.
I am trying to get the timing of the next steps figured out but I am stressed out because of a piece on the Sakrete site that says with their sandmix tile has to be laid at 16 hours or you have to wait 28 days. Yikes! Is that for real?
Specifically, this the quote:
Set Your Tile Within 16 Hours

I didn’t know this until researching to write this post, but you should set the tile floor while the mud is still fresh, before it gets “green” in the curing process. So either set tile that day or the next, or wait until the sand mix is cured, which takes a few weeks.
Even though I used the Quikrete product I assume they are
basically the same thing. What would happen if tile was laid on green cement?

07-11-2019, 07:21 PM
Waiting overnight is usually good enough. You want it hard enough that it doesn’t abrade as you’re working on it.

07-11-2019, 07:29 PM
I don't know of any reason to wait 28 days to set tile over the floor.

07-11-2019, 07:29 PM
Those are some directions! Sounds like they're trying to force you into getting those tiles put down soon, or you're gonna be just sitting there watching Crete cure.

I vote for 28 days is not necessary. Personally, I would wait no more than 3 days, but I'm crazy, so take it as you will.

Sent from my SM-G930V using Tapatalk

07-11-2019, 08:18 PM
Thanks for the reassurance. Just to double check-its ok to embed Durock in my top layer of mud?

07-11-2019, 08:23 PM

07-11-2019, 09:50 PM
Leave the edge of it up about 1/2" or so off the liner.

The manufacturers of the fiber cement boards don't allow them to be buried in the mud, so if you can't get Durock, go with one of the other true cement boards like Permabase or Wonderboard.

08-15-2019, 11:11 AM
I was making good progress on tiling my walk in shower until I removed the ledgerboard I installed a week before and discovered several areas where the now very hard Versabond had leaked down. I have made little progress with a masonry chisel and I am afraid I will crack the installed ceramic tile if I persist and get into a worse mess.
I have Durock walls with Redgard.
I have thought about using a grinder with a masonry wheel but that would mess up the Redgard.
Any ideas on how to fix this? I am a little desperate since I am on a tight timeline and I intended to grout this weekend.

08-15-2019, 11:12 AM
Sorry that the pictures loaded sideways

08-15-2019, 11:53 AM
Hammer and chisel, not to break it it but to score a line then take a margin trowel or pitty knife and pry it up away from the wall. Then take some Redgard and paint it on over any suspect areas