Slate tiling job - uneven floor [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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05-07-2014, 02:59 PM
Need a little advice please - My husband and I bought an old restaurant that we're renovating into our home.

The old commercial kitchen (all 500 sf of it) had a linoleum tile over plywood floor, that (due to a failing drain system that we have decommissioned) was falling apart, so we've removed the plywood and found another layer of linoleum on the concrete floor. Most is well-fixed to the concrete, but some tile has lifted off.

So, my question is: if we do a medium bed or mud mortar, can that help us even out the 3/16" difference between the bare concrete and the remaining tile? We're putting down 16" x 16" x 3/8" gauged slate tile. I would REALLY prefer to not have to remove all the tile that's on the concrete. It is very well-fixed, I'm assuming it's likely asbestos, and the less I have to break it up, the better.

Thank you!

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05-07-2014, 05:12 PM
Welcome, Sara. :)

I can't really tell what you've got in that photo.

The lighter gray areas that appear to have a grid marked on them are?

The blue is the VCT?

The holes and gaps in the light gray are showing the actual concrete surface?

Please strike the term "medium bed" from your thinking. No such product exists in the ceramic tile industry and that which is commonly called by that name is a thinset bonding mortar and not to be used for truing or leveling of any substrate.

The only way I can see that you could reasonably tile over what we see there (once we find out what we see) is to use an unbonded reinforced mortar bed. That would need to be a minimum of 1 1/4" thick with welded wire mesh in the vertical center.

If that's not an option you might want to look into hiring someone to come in and scrape and mechanically scarify that floor in preparation for a stone tile installation. If the surface flatness is not sufficient for your tile size (no deviation from required plan of more than 1/8th" in ten feet nor 1/16th" in two feet), you'll need to deal with that at the same time.

If you wanna do it all yourselves, you'll likely wanna rent some larger equipment than you might have in your arsenal.

My opinion; worth price charged.

05-07-2014, 05:54 PM
Thanks for the reply!

The lighter gray/beige is the existing linoleum tile. The "blue" is the concrete (still has some old adhesive on it.) That's it, there's just the two surfaces, the concrete, and the tile, 1/8" difference in height. (The thicker stuff to the right on the image is the old plywood/tile layer that we're removing.)

I had hoped that since we were working on concrete, we could use a mortar with a larger sand (what I had read was Medium Bed Mortar on the TCNA website) and just build it up higher on the slightly lower areas of concrete.

From the TCNA website: Medium bed "thinset" mortars can be used to adjust for slightly larger variations in the substrate than can be accommodated with thinset mortar. They are also used with large, heavy, or thick tiles where a thicker setting bed and a coarser aggregate may be required to achieve a flat installation and to support the weight of the tile while the cement is curing.

Which sounded like exactly our situation. I also found products that are described as medium bed mortars so I thought we were all set.

So I'm totally confused! Anyway, if your advice has changed with the further explanation of our conditions, please let me know.


05-07-2014, 06:12 PM
There's no way I would tile over that VCT. Looking at the bottom of your pic, if it will come up in pieces that big, it'll come up. I'm sure it's stuck better in the traffic pathways.

Many times there is more time spent prepping the floor than actual tile setting. It's very important if you want a long lasting floor.

One way or another, I would remove that VCT and then Like CX said, " mechanically scarify that floor in preparation for a stone tile installation".

05-07-2014, 06:21 PM
Got it. Thanks guys!

05-07-2014, 11:31 PM
Good to see you were doing your homework there, Sara. I suspect you'll see a change in that wording in the TCNA Handbook soon, though. Much discussion was had on that very issue at a technical committee meeting before Coverings last month and the problems with misunderstanding of the purpose of those products.

Those bonding mortars, like all other thinset bonding mortars, are not intended to be used to flatten or level the tiling substrate. That should always be a separate step in the tiling process. But it's become clear that the users are viewing the mortars with the "medium bed" properties as something to be used as a flattening/leveling material rather than the intended purpose of bonding.

Now that I see which is which on your floor I most certainly gotta agree with Davy. I just wouldn't recommend you do what you have in mind.

My opinion; worth price charged.

05-08-2014, 08:24 AM
Interesting. That's definitely how I read it, glad they're going to change it. Thanks very much for all the fantastic advice. What a great public service...all to avoid the sin of bad tiling I guess?

So it's been me and my heat gun for most of the last 18 hours (averaging about 7-8 minutes per tile) but nearly all of the old tile is up in the section we're planning on doing this weekend. Going to the next step though brings more questions! Please, if you can:

1. We are staging the demolition/installation to do half the room now, then tile/grout, move everything over and then do the other half. We just have too many things in the kitchen and no other space to move it to. Do you foresee any issues with doing the job 1/2 and 1/2? How much time should we wait to move heavy things (like a refrigerator) onto the new tile?

2. The concrete that's left after the linoleum tile removal has a good deal of adhesive still on it. I know I need to get that off and rough up the surface, but hiring people with giant machines isn't an option for us. Am wondering if something like this TE-905 tool ( with the bushing attachment would be enough to scarify the floor so we get good adhesion?

3. We have a 16" x 16" x 3/8" Brazillian Black Slate cleft-front/gauged-back tile. I've installed this tile once before in a small kitchen, and the stone importer I worked at the time for recommended a non-sanded grout because this slate is fairly soft and prone to scratching. I believe we did a 1/8" grout line and it turned out beautifully. But it seems like most of you recommend a sanded grout, so I'm confused. Is there a real downside to using the non-sanded? I know there can be shrinkage, but I think before we were careful to not remove too much when we were wiping off and even though it shrunk it was fine. I've had bad experiences with sanded grout ending up pitted and weird, and they also seem more porous and seem to hold dirt, so I think I'm inclined to go non-sanded if you guys don't object.

Thank you Thank you Thank you! :D

05-08-2014, 09:58 AM
Hi Sara. The bushing tool will work although a slow process. But, I don't know of a better or faster way without some big equipment.

If that slate scratches that easy, I would second guess using it. I've installed tons of slate and have never used non sanded grout. Many times, slate is cut out of size so bad that the grout joints will vary, some might go to 1/4 to 3/8, some 1/8. The joints will stay fuller with sanded and it will be easier to grout.

As far as leveling with thinset, like CX said, it isn't designed for that but it does work. I hate using SLC for leveling and it's more expensive than thinset. Some SLC's need a primer first and I feel like thinset sticks better to thinset than it does to SLC.

05-08-2014, 11:27 AM
Thanks. Already bought the tile, so I think we're stuck! I'm considering the sanded, easier sounds better, and with a cleft face I don't think any tiny scratches are going to matter. That's going to happen with normal wear and tear anyway. I honestly don't think it's all that soft, our old floor wore fine, the old importer I used to work for was usually working with polished materials, so I think that's why they were always recommending the nonsanded.

After I remove all the tile (nearly done!) we will be dealing with a totally flat surface, so I don't think SLC will be necessary. I just picked up that light-duty drill hammer but with a flexible scraper bit, which is doing a nice job of both removing the adhesive and scarifying the floor, so I think we're good.

The only other question I have is that there are spots where nails came out and brought a bit of concrete with them. They are probably every 2 feet, and only about 2" in diameter, and not more than 1/4" down, just little spots. Are those ok to fill with thinset or do I need to fill them with some sort of special concrete patching material?

Thanks again! :)

Richard Tunison
05-08-2014, 11:47 AM
Thinset will be fine. You might have to hit em' twice to get things even as the first lift will probably shrink a bit.

MAPEI - Technical Service
05-08-2014, 11:52 AM
As for grouting, you may be better off with one of the new ready-to-use grouts out there. They work at a variety of widths. Our Flexcolor CQ has a round aggregate that won't scratch as easily as typical sanded grouts. The color consistency is also better if you're planning to do 1/2, then wait, then do the other 1/2. The product will stick to itself too which makes blending easier. You can read more and see some testimonials on this thread:

Your question about when you can move your heavy items onto the floor depends on what you're using for a setting material. Whatever you choose should let you know in the technical data sheet how long to wait. For example, our Ultraflex LFT recommends 7 days (and I would wait that long realistically):