Tiling over moist limestone ? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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Debra L
05-19-2019, 10:10 AM
After reading this I realize I should not have used natural stone on shower floor but I had no idea I was buying limestone and trusted the person who showed this to m. Installer did not pre seal limestone before grouting on shower floor. It absorbed water and looks horrible. I was able to dry it out with a heat strip but it took HOURS. They then tried to seal it and same problem. I have opted for porcelain as I do not want to go through this again. Their solution is to tile over this and not take it up. Is this ok? My concern is moist stone will be trapped under the porcelain.

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Debra L
05-19-2019, 10:16 AM

05-19-2019, 10:34 AM
Hi Debra, welcome. Presealing would not have helped.
Do you know what type of waterproofing is under the floor tiles?

Debra L
05-19-2019, 10:47 AM
Unfortunately no. It has a mud bed and a layer of some type of membrane.

05-19-2019, 11:18 AM
It looks like a Kerdi grate. Assuming installers wouldn't use this unless using a surface membrane. Debra, do you remember seeing orange on the floor/walls at some point?

If it's a surface membrane, removing pan tile will likely damage it. Redo is a huge job. Tile over tile is viable if done right, and would preserve waterproofing.

I'd be curious how they intend to deal with drain grate height as that's kinda fixed now. I've never tried to break the drain grat loose on Kerdi drain after the fact, but it's conceivable it could be done without compromising waterproofing.

Debra L
05-19-2019, 12:52 PM
I do not remember seeing the orange membrane but I definitely recall them talking about putting one. As for the grate, it is slightly too high as of now. Water puddled slightly to left of drain.

I did see on another website that there is a piece which can be installed on top of current drain pipe to raise it higher.

So I am just the customer who has done as much research as I can to understand what is going on and that it will be done right. I also would love to get this wrapped up!
From what I gather here, even if the stone has retained moisture, it is still better to tile over this rather than taking up current tile?

05-19-2019, 01:07 PM
I question whether the drain extension was intended for a Kerdi drain, which is a unique animal. Can you link what you're talking about?

As to a "better" way. I can tell you it's a viable method if done right. Prep existing, raise grate, preserve waterproofing. One measure of this would be the workmanship warranty of installer and the confidence in providing a long term solution.

The above assumes that original installation was done according to waterproofing manufacturer's specific instructions. Can't make something better by just heaping more of same on top.

Is this your nickel or installer's?

Debra L
05-19-2019, 01:32 PM
This is the installers “nickel “ and I had someone else do the demo of existing shower because they were doing other repairs.
However, this installer was particular about wanting to do plumbing to finish because then I would have no question as to whom would be responsible if issues arose. He said they have never encountered a situation quite like this and is trying to make this right.
As for long term, he took over this particular business 12 years ago. I used the original owner 35 years ago when building my first house. I trust him as much as I can to make it right.

I can’t say that this is a Kerdi drain because I am not familiar with the terms. It was just a product I saw on line and when I searched just now I found one called extendo drain. It consists of washers and a plastic fitting.

05-19-2019, 01:40 PM
Definitely a Kerdi drain....which presupposes that it is a Kerdi membrane floor. I would imagine that the tile could be removed carefully and it may or may not damage the membrane, although fresh Kerdi membrane might be able to be reinstalled for the fresh tile.

05-19-2019, 02:35 PM
This the Extend-O-Drain (https://www.stonetooling.com/Extend-O-Drain-Height-Extension-Kit-p/40-00179.htm) you're talking about, Debra? If so, that's not gonna work with a Schluter drain.

While I've never tried it, I think it likely possible that a fella could chip out the drain grate assembly and replace it in a new tile-over-tile installation. The first part of this video (https://www.youtube.com/watch?v=Ta_Kf0dCd3U) would give you an idea which part I'm talking about. I think Schluter would be willing to provide the needed parts. If not, buying a new drain assembly might be necessary.

I think your chances of actually removing the existing tile from the Kerdi membrane on that floor while maintaining the waterproof integrity and the fleece condition necessary for a replacement tile installation are right about zero. Realistically, probably a little less than that.

My opinion; worth price charged.

Debra L
05-19-2019, 04:52 PM
Thanks to all who have replied. I have watched videos of Kerdi drain and understand the problem. I do recall Kerdi board on the walls, curb and bench. I was not here when floor was installed but because of the unusual shape, they did a mudbed. I remember the center drain part being raised and was large like the Kerdi. There was miscommunication between the plumber, tile installer and contractor so for some reason tile guy installed drain which may not have been great. Watching videos I see where the tile is set from outside finishing in the middle. He definitely did NOT DO THAT as he set tile around drain first and came back another day to finish the rest of the floor.
Hence the floor does not slope properly to the middle. I do not know how they will handle the slope and drain but I at least know some appropriate questions to ask and am comfortable with them tiling over existing floor if necessary.

My concern was if the moisture in the existing tile would cause problems in the porcelain which would go over it. From what I am seeing is the drain is as big or bigger an issue.

05-19-2019, 05:08 PM
Most any tile contractor will tell you he'd much rather install a Kerdi-type drain than let any plumber handle it.

Starting the tiling at the drain did not cause a problem with the slope of the floor if the floor was done properly to begin with. Incorrectly installing the tile near the drain could be the problem, but not because of where he elected to start installing his tile.

My opinion; worth price charged.

clifton clowers
05-19-2019, 09:34 PM
The Schluter drain grate consists of two pieces of metal connected via 2 screws in the corners. I think they are M4 threads. If it is already installed, the top piece of metal can be removed by removing the screws and reattached with some small, stainless, Male/Female M4 spacers raising the height of the drain to accommodate another layer of tile.

Is it ideal? Probably not, but it works fine. The worst thing that happens is you are back to where you are now. It is also a good idea to epoxy some Female/Female spacers into the other two corners for added stability.