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HavFixFun 11-09-2017 08:16 AM

Flat but not level shower
First time user, DIYer, and love to learn. I really appreciate this site; it has been a great help to us.

We are the owners of a sixth five year old house in NW Ohio. We're in the middle of remodeling a 1/2 bath, laundry and garage entry area of about 150 sq ft total. We have new exterior grade 3/4' OSB over 2 x 12 joists in really good shape over a crawl space. Deflection is good.

While this shower pan area is flat, it is not level as we discovered upon fastening the durock to the back wall. The shower area is sloped away from the wet wall such that we are 1/4" low on the wall opposite the wet wall. The 2.5' x 4.5' alove shower is 1/2" durocked all around. The floor piece of durock is fastened with thinset and Rock On screws.

We intend to use the Kerdi Shower Kit over the durock, using Schluter All Set and then travertine 2" x 2" mosaic on the floor. Since the kit's pan is 1/4" slope/ft, we definitely want the slope eliminated.

My thought is to use All Set thinset to 'level' the durock floor by skim coating the low part, waiting for it to cure completely, and recheck for level. I would grind off any rough or high spots and then carry on with All Set and Kerdi Membrane. Thoughts and suggestions? I love to learn!!

Kman 11-09-2017 02:26 PM

Welcome to the forum. :)

I moved your thread over here to the advice forum where more eyes are likely to see it. The mud box is for anything that doesn't fit into the tile/stone categories.

As you have probably read somewhere, the floor has to be completely flat and level to use a shower tray. Tilting in any direction will affect how the shower drains.

It would have been best had you not added Durock to the shower floor, unless you just want the extra height. The tray can sit right on the plywood. Also, what is the joist spacing? If it's more than 16", you would want to add a layer of 1/2" plywood to reduce deflection between the joists.

The foam trays can be a time-saver if your floor is flat and level, but we most often recommend building a shower floor with deck mud, as it compensates for floors that aren't flat or level, not to mention it costs much less than the foam tray. It is a little more work, but most folks that come here aren't afraid of that. ;)

HavFixFun 11-13-2017 07:49 AM

Thanks for moving the thread over, Kman.

The joists are 16" OC. I am embarrassed that I could miss such a thing as level, but we are where we are and mistakes are good for learning from.

I covet your counsel on what to do now. With a steady slope that is 7/16" from right (wet wall) to left in 52" we need to do something over the durock.

I've asked around among my friends and acquaintances and I'm getting, "you can use SLC over any concrete product, durock included" and "use deck mud to level on the left reducing thickness to a skim coat as you approach the right wall", and "just build up thinset on the left a bit when setting the Schluter pan and then again when you apply tile onto the pan to correct the slope".


Kman 11-13-2017 12:16 PM

It would probably be best just to use one product to do the whole thing, which would have to be either a self-leveling compound that can be troweled down to nothing, or something like Ardex Feather Finish.

Both of those are fast-setting, which means you have about 15 minutes to get them down once you add water, so have everything ready before you start. You might use something to mark the level of the compound within the shower, such as masking tape, a sharpie, or even some brad nails.

I'd use a straight edge to work the material off and get it flat and level before it sets.

HavFixFun 11-14-2017 06:12 AM

Thanks for staying with me Kevin. With your help, I am upping my game to avoid other mistakes, so thank you very much.

Realizing that prep is key, I have a couple more questions:

What do you recommend I dam the gaps at the durock edges with?
The drain hole is cut; how do you recommend I dam that?

I've seen videos referring to silicone caulk at wall edges, some blue foam stuff along walls that looks like a temporary baseboard, and what looks like plumbers putty around drains.

Finally, would you use primer on the durock surface or treat it some other way before applying Ardex Feather Finish?

Kman 11-14-2017 07:36 AM


What do you recommend I dam the gaps at the durock edges with?
How big are the gaps? Is this just between the wall and the Durock? If so, just some spray foam insulation would work.


The drain hole is cut; how do you recommend I dam that?
Depending on the size of the hole, a PVC union will work. If it's larger than 5" you'll have to use something else. Maybe some sheet metal that you can fashion in a circle to the correct size, or some roll flashing.

The things you mentioned will also work.

I don't think Ardex requires anything as a primer. Immediately before putting it down, I would dampen the floor with a sponge to keep it from drawing moisture out of the material prematurely.

HavFixFun 11-14-2017 07:53 AM

The gap is a smidge over 3/8" at the left wall and gradually declines to level at the right wall over a length of 52". This slope is consistent across the surface front to back.

John Bridge 11-14-2017 08:31 AM

Hi and welcome. Maybe give a first name or nick name for us to use. :)

I might have missed something, but I think the Durock should be removed from the floor before using the leveling compound. :)

Kman 11-14-2017 08:42 AM

I agree that it's of no use at this point, and I mentioned that earlier, but it's down with thinset underneath, so the only thing it's doing is adding 1/2" to the shower, so no harm done.

HavFixFun 11-15-2017 03:40 PM

The process continues. Thanks for staying with me. It will help to know that a 32" x 60" center drain Kerdi Shower Pan is being used.

A wise friend counseled me to cut and dry fit the foam pan and check for level before taking the drastic action of putting SLC over Durock. He confirmed my measurements with a Bosch self leveling laser (a new model GLL3-15). It was sloping 7/16" over 47" (the first 5" on the high side were actually level, then the slope begins, so it was actually WORSE than first thought! We measured and cut the foam Kerdi pan. The drain, which is nearer the low end, meant we needed to cut the pan on the lower end of the shower floor. Once the pan was cut to fit, we slid it into place to check level. Surprisingly, the slope was more than sufficient in the pan to overcome the confirmed the laser confirmed slope! A 2' level, placed on the low end to the drain, shows an extreme left of center bubble--we were amazed and please to say the least! All we can deduce is that Kerdi builds more than 1/4"/ft slope into their foam pans. No SLC...whew!

I learned a valuable lesson; some things just aren't as they appear! Dry fitting and remeasuring saved me a bunch of money, time, and effort!

The next hurdle is a Schluter profile question. Their popular DILEX and RONDEC profiles are planned for this project. We'll use some sort of edge for the tile ends (since the tile's bullnose is a horrible color mismatch), but want to know if anyone has any experience with this stuff. Is it worth the effort?


Gozo 11-15-2017 07:25 PM

The profile look depends on your personal taste. Because of the position of the door frames at either side of the shower, I used bullnose on one side and Rondec on the other. Looks OK to me, but I had planned on that look from the start of tile setting.
Take a look at the 1st and 2nd pics in my build thread here.

HavFixFun 11-16-2017 07:24 AM

Thanks for the response, Jeff. Great looking shower! I'd like to read more of your stuff. What is the thread name of your project?

HavFixFun 11-29-2017 08:25 AM

The project continues and I have more questions (of course).

I have leveled the floor (outside the shower) with Mapei Self Leveler Plus. With the plan to lay 12" x 24" porcelain tiles in about 115 sq ft:

What's down: 3/4" OSB over 2x12 joists 16 OC, Mapei Primer T, max of 1/2" of SLC per above:

1. Would you recommend a layer of 1/4" HardiBacker or do I lay tile on SLC with thinset?
a) if I need HardiBacker, how do I affix it to SLC?
b) if I don't need HardiBacker:
*is Ditra overkill or will it add significantly to the security of the tile to justify the cost?

2. I've read that 1 1/4" is proper substrate thickness. With what's down, I have that, if SLC 'counts'. A Lowes associate said HardiBacker over SLC with BackerOn screws; is this legit advise?


Kman 11-29-2017 09:35 AM

Assuming your joists are not overspanned, you would want to add a tile membrane to the SLC layer, such as Ditra or Stratamat, then your tile.

You can't put a cement board over SLC. Typically you would put down cement board first, then SLC.

HavFixFun 11-29-2017 04:58 PM

Joist are 12' long so using DITRA should be a good next step; thanks for the input! We plan to apply it with ALL SET thinset to stay in the Schluter family.

SOOOOOO, I just checked out the Mapei SL Plus pour we did yesterday. There is a 'ridge' where the last batch ran into a previous batch and it looks like it didn't make it all the way into the corners to cover the sill seam I used as barracade either. It looks like the mix was just too thick, even though we followed the directions (73 degrees, low humidity, 5 1/4 qts of cold water per bag, etc.) I see I'm not the first guy to experience a problem like this. I read thoekstr's "SLC didn't level out flat - help!" thread that was referenced at the end of our exchange. HELP! Can you advise on what you would do and what you would use to level out the first pour? Is a second layer ok?

1) I've got about 115 sq ft; do I just pour it thinner and at a lesser depth over the entire area?
2) How do I make sure the two pours bond?
3) Should I just mix the same product from Mapei only thinner like 'chocolate milk' as suggested in thoekstr thread?
4) What do you suggest I use to 'help it' or will the SLC actually level itself without help if it is thinner?
5) If I used 8 bags (50 lb each) for this space the first time, how much should I have on hand for a thinner 2nd pour, if that's the next move?
6) Any suggestions on how much water to add to make it thinner, if that's the way to go?


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