Cracks in Pre Slope [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-09-2003, 07:41 AM
Hello all:

Been doing lots of reading on this site. Thanks for such a great site. Starting major bath remodel to include tile shower with masonary monument seat, tile floor and tile around soaking tub

I know everyone likes pictures so I have uploaded several to:

Followed combination of several of the Liberry articles to start the tile shower.

Felt paper with lath generously stapled to sub floor of two sheets of plywood 1/2 and 5/8. Plywood nailed and screwed to 2x10 floor joists on 16 centers. House is about 15 years old. Shower being installed in a former tub shower combination alcove 40x60 in size.


I thought I was doing pretty well but after installing pre-slope, I noticed several hairline cracks appeared in pre-slope around the thin area around the drain. No cracks in the outer edge area of the preslope. If I step on the preslope around the drain, I notice slight movement. Sub floor was pretty solid, but since it is wood not perfect, I suspect this might be combination of small movement in the lath concrete combination and a little plywood flex. Do I need to worry about this or will the mortor bed bridge over this the create a solid floor.

I am sure this will be first of many questions. I will continue to post pictures of progress.

Thanks for your advice,


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01-09-2003, 09:59 AM
Hello Pete,

Welcome to the boards, the pros will be along shortly to answer your questions. Took a peek at your gallery pics, looks like you're on the right track. Happy tiling and keep us posted. :D

01-09-2003, 10:09 AM
The mortar bed will be 1" thick and have lath bedded in it. Should work. Preslope just shapes the liner to guide the water into the weep holes.

01-09-2003, 01:12 PM
It wont matter. The pan is going to act as a slip sheet between the new setting bed and will prevent the crack from telegraphing through to the new floor. I think your preslope was probably too thin at the drain. Your finish slope has min 1" of mud at the drain.

01-09-2003, 06:32 PM
Hi Pete, welcome. :)
That's a good looking shower so far. I was told minimum of 1 1/4" of final deck, 1 1/2" is better. I was also told not to bother with lath in the final deck, although some guys do it. :) Are you going to fur out the studs with 1/4" lath so that the cbu doesn't bulge at the bottom from the liner?

01-09-2003, 07:20 PM
Great looking shower. You are missing some blocking along the two stud bays where your supply lines are. No big deal, but I would block those areas with narrowed recessed blocks sistered against the studs and some three quarter plywood spanning the stud bay. This is especially important if you are using Hardibacker, which requires blocking on all four corners.

John Bridge
01-09-2003, 08:34 PM
Hi Pete, Welcome. :)

No problemo.

I'm looking at your curb, though, where it angles into the end wall. When you mud it, it's going to be sticking out beyond the end of the wall. I wonder how you'll handle that.

01-10-2003, 11:35 PM
Thanks for all of your advice:

Couple more questions and some replies to your advice:

Plastic or roofing felt for moisture barrier. Seems most use plastic, I have both, any advantage of one over the other.

I have some Custom float bedding mortar, leftover from preslope, seems you guys like the Sakcrete sand mix, can I mix the two for my final deck mud. I take it they are the same, but Sakcrete is just cheaper.

John B./Davem, In the shower seat article you built your monument seat directly on top of the membrane and then floated the floor later, does it matter if I floated the full floor and then did the monument seat on top of all of that or is it preferred to build the seat structure first and then float the floor up to the seat. My thought for doing latter was to have a nice continuous final deck an also to stay off the membrane as much as possible after it is installed.

In Tom Meehan's shower pan article on Cape Cod Tile, he mentions putting felt paper between the preslope bed and the membrane as an extra layer of protection for the membrane agianst abrasion. That sounded like a good idea but haven't seen anyone else mention doing that. I also thought I would run felt around the bottom of the floor between the blocking and the membrane to protect against any protruding blocking nailheads etc.

Plan to take BBcamp's advice and put lath in the middle of the final deck just to help with any floor flex and will plan to do 11/2 thick final deck.

Davem: affirmative on putting in 1/4 furring strips to help smooth out walls for membrance thickness.

Scooter blocking you see out was at top of old tub, will be adding an additional 2x4 blocking on top of the 2x6's I initially put in for the bottom blocking to insure adequate support around bottom of base.

Planning to use Hardibacker on the walls since I thought that was superior to durock, etc, but after reading Tileguytodd and others on this site not so sure, but it has been bought and to much work to return.

John: Thanks for you detailed look at my curb. I think I might be able to make what I have work. Curb at angle corner does sit back about 5/8 from edge of drywall on endcap of wall. If I make curb 3/4 thick and put tile on wall end cap (Anyone have any problems with tile on the end cap wall), with angle of wall I think mortar joint between end cap tile and curb tile can make up the difference and will look okay. Other thoughts or ideas welcome.

Planning to work on finishing up the block, furring out and installing a pro form niche tomorrow, and try to get some upper layers of hardibacker on as wel as install the membrance, will post more pictures of the progress.

Thanks again for all your help.


John Bridge
01-11-2003, 01:46 PM

Doesn't matter whether the seat is above or below the floor.

The tar paper won't hurt, but it's not necessary. In the old metal pan days (lead and copper) they used tar and tar paper to separate the metal from the cement, and the practice carried through. PVC and CPE don't really care what they are up against.

01-13-2003, 10:55 PM
Well I got the blocking in around the bottom and in the middle at the hardibacker joints so all edges of the hardibacker have support. Went with plastic for the moisture barrier and hung the upper layers of hardibacker and installed the proform niche, which by the way is waterproof. I filled it up with water and put it in the bathtub overnight to test it. No leaks.

Put felt paper down on top of the pre-slope and around all the lower blocking to help bridge the gaps a little and provide a smooth surface for the PVC liner.

Got the pvc liner in but have some question about properly attaching the dam corners. I used silicone caulk to attach them, but not sure if that was correct, the silicone isn't real sticky and the corners will pull away from the liner. Should I have used PVC cement. Went with the caulking because corners don't fit tight as a result of the angle of curb. It looks like silicone caulk will peel right off as I tested by caulking two pieces of liner together, should I peel off, start over and use the PVC cement.

Another question, when attaching hardibacker on horizontal surfaces of tub should I put thinset on the framing top plates and then screw the hardibacker strips to the two top plates or can skip the thinset and just screw.



Updated pictures posted to

John Bridge
01-14-2003, 07:04 AM
Thin set is always a good idea under horizontal CBUs.

They make a special glue for seaming PVC liners and for attaching the corners. Oatey's product is called X-15 (Home Depot).

Mark R DIY
01-14-2003, 11:15 AM
Pardon my ignorance, but what are the black pieces on the curb?

01-14-2003, 11:33 AM
the black things are shower damb/outside corners. several mfg. offer them. they are avalible on line at or in some areas H.D.

01-14-2003, 09:10 PM
Got the X-15 pvc cement this evening and will glue up this evening.

How long do I need to let it dry before doing the leak test.

When putting up the lower CBU/Hardibacker board in the shower, I think I am suppossed to hold it that off the bottom of the pan a 1/2 inch or so, do I hold it off the sides and top of the curb as well.



01-15-2003, 08:55 AM
recently saw product called pro form IT IS A PRE MADE CURB!

01-15-2003, 10:20 AM
I'd wait 24 hours to do the leak test, although that stuff cures so quickly overnight would probably be fine.

I hold the CBU's off the pan.

I don't hold them off the top of the curb, only about sixteenth or quarter or so. Same for the sides of the curb. The two materials between the curb and CBU are more or less mushed together when you tape or when you apply the trowel on waterproofing, e.g., tape and thinset, and fabric and latex. No big deal there.

The ProForm curbs don't work well with hybrid showers and are better suited for showers that use their own CBU because of thickness issues. An you have a split curb with an angle in it, too. Proform is better suited for straight lines.

John Bridge
01-15-2003, 09:36 PM
Thanks, Info, but we're already beyond that point on this one. :)

Yes, you should wait overnight, but you won't be testing the curb corners anyway. You won't put that much water in your liner. The curb corners more or less deflect water that hits and gets into the top of the curb. Doesn't have much to do with the pan test.

02-25-2003, 09:54 PM
Its been a while since I posted. Been been busy tiling.

Updated photo's at

Sorry to have to use the links but I haven't figured out how to post directly to site and to reduce size of picture. Didn't want John to yell about bandwidth.

My questions is do I need to caulk corner joints in shower and between floor and wall tile or can I grout. Seems I have read that some just grout everything now when the wall length isn't that great. Back shower wall is 5 feet across, walls are 8 feet high.

If caulking is the way to go how do you keep it from discoloring over time. Caulk used with previous cultured marble would mildew within the year after installation. I really don't want to have to replace caulk constantly. Is caulk from Color Caulk more resist to mildew, discoloration.



John Bridge
02-26-2003, 06:38 AM
I would grout it, Pete, but that goes against the book, which says to use caulking. ;)

02-26-2003, 06:50 PM
Thanks john for your quick reply.

I will plan to grout even thought it is not TCA approved as I really hate the idea of dealing with caulk.


02-26-2003, 08:16 PM
Been been busy tiling.

Understatment of the year, Pete. :D Great looking job. :shades:
I see you had a helper, looks like a master with a margin trowel. :p

02-27-2003, 11:57 AM
The pictures look good. I have a couple of questions because I will begin identical work this weekend.

1. I want to know if that is greenboard on the ceiling in the shower stall or is it regular drywall. Is it 1/2" or 5/8"? I ask because I was told that I could use regular drywall on the ceiling.

2. It appears that the remainder of bathroom is regular drywall. Am I correct with my assumption.

3. Where did you purchase the soap/shampoo holder?

Thanks in advance for your info.

02-28-2003, 12:21 AM

Very impressive work. Nice attention to detal, primarily where it never gets seen..under everything.

02-28-2003, 05:46 AM
Nice Job Pete,
I think you qualify for the wall of Fame :)
Why dont you send john a couple finished pics that he can post in our members album.maybe we'll make ya famous!! :D

02-28-2003, 12:32 PM
Originally posted by Methodical
The pictures look good. I have a couple of questions because I will begin identical work this weekend.

1. I want to know if that is greenboard on the ceiling in the shower stall or is it regular drywall. Is it 1/2" or 5/8"? I ask because I was told that I could use regular drywall on the ceiling.

It is greenboard on the ceiling in the shower. It is 1/2 to match with the rest of the ceiling drywall. I used greenboard as I didn't want to take any chances with the regular stuff. It is not a steam shower, but I like to take long hot steamy showers and that moisture will go up.

2. It appears that the remainder of bathroom is regular drywall. Am I correct with my assumption. All drywall around soaking tub is also greenboard. The rest is regular drywall.

3. Where did you purchase the soap/shampoo holder? Holder was purchased from local tile store. I believe you can purchase same or similar from one of the board contributors at Several other companies make similiar items. Search the forums for shower niches.

Will send/post some final pictures when its all done.


Thanks in advance for your info.