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Unread 08-05-2020, 02:02 PM   #1
Jason_Z
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Want to tile over 9" Vinyl Tile in Basement

Hi,

Planning a basement renovation - there's some 9" vinyl tile in the basement held down by black cutback adhesive. Have not had anything tested yet but treating it with an abundance of caution.

The floor is not level, it's concave by about 1/2" over 10' span. The floor is 50 years old and has no visible cracks.

I would like to use large format tiles, 13x20" porcelain, so I expect I'll have to level the floor.

These are the options I'm considering, I think I would prefer #1 or #2. What do you think?
  1. Leave the vinyl tile alone and use primer and SLC on top. Is this an option? Is there any SLC that can be applied to primed vinyl tiles?
  2. Remove the vinyl tile but leave the cutback adhesive, and level the floor on top of the cutback adhesive. I'm trying some modified mortar on some of the cutback adhesive now to see what kind of bond I can expect... I've read on this forum that there are modified thinsets that can work on cutback adhesive, but I'm not sure if that also applies to self levelling compounds or if my modified thinset test is even worth doing.
  3. Remove the tile and cutback adhesive. I don't want to have to remove the cutback adhesive if I don't have to..
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Unread 08-05-2020, 02:17 PM   #2
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Welcome back, Jason.

Just as with wallpaper, one sure way to remove VCTs is to install ceramic tiles over them. There are probably combinations of various primers and SLCs that would allow you to do that, but I sure wouldn't.

Every tile installation product you'll find that indicates use over cutback adhesive requires that the cutback be removed to no more than a stain.

If the cutback material contains (testing is readily available) asbestos, grinding is usually not recommended. If it doesn't contain asbestos, I would recommend mechanical scarification of the concrete surface before installing ceramic tiles.

You say you want to level the floor. Your tiles don't give a rat's patooti whether your floor is level, they care only about flat. And for the size tiles you've selected that means no deviation from intended plane of more than 1/8th" in ten feet nor 1/16th" in two feet. That's a very, very flat floor.

You'll need to check with the manufacturer of your chosen SLC to determine their position on installing over cutback residue. At very best I expect you'll find the same as for the thinset mortars, but the SLC manufacturer might not recommend their product at all in that application. They generally want a very clean, primed surface.

My opinion; worth price charged.
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Unread 08-05-2020, 02:20 PM   #3
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Hi Jason,

We'll have to decide on a SLC manufacturer and contact them. I sure don't know the answer. What brand do you have or plan to use?
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Unread 08-05-2020, 03:16 PM   #4
Jason_Z
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Hi guys, thanks for the replies and the welcome back.

The kitchen remodel went amazing. 13x20" porcelain tiles over new 3/4" T&G plywood subfloor, 720 deflection ratio, mortar, 1/2" CBU, 1/2" trowel mortar, and then just made a transition strip from the tile to hardwood floor. Custom frameless cabs from Barker Cabinet, travertine backsplash, quartz counter, Kohler whitehaven apron sink




I don't have any SLC yet. I just have "TEC Totalflex Universal (modified) Mortar" that I purchased a while ago as a $5 broken bag to play around with. I have a few test patches on the cutback adhesive and normal exposed concrete... Not sure what it will tell me if anything...

I read some threads on here previously that recommended using thinset directly on cutback adhesive, and not to remove the cutback adhesive... because apparently there will always be a thin film of adhesive anyway and its not worth the effort trying to remove... But Im not sure if that advice applies to SLC and/or if that advice is even still relevant?

Are SLC's and thinset mortars equal when it comes to bond strength or is one better?
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Unread 08-05-2020, 04:50 PM   #5
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The question isn't so much about bond strength as it is what the substrate is. I'm not familiar with any mortar or compound that the manufacturer recommends using over cutback. There may or may not be one out there that I'm not familiar with.

You can see what's available in your area and find out if it'll work in your application. Then spread out to see what you can get that's not local and try again.

If it were my floor and I were facing what you are, I'd probably consider a different type of flooring. But if you want ceramic tile, there's a way to get it done, it just might be more work or money than you want to do.
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Unread 08-05-2020, 05:08 PM   #6
Jason_Z
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Ok so Im reading the datasheets for
  • CBP LevelQuik® RS
  • CBP Versabond Fortified Thinset Mortar

Both are acceptable to use on cutback adhesive residue - they do not want me to use solvents to remove - only wet scraping. How does wet scraping really work if the concrete floor isn't perfectly smooth? Wouldn't it only expose the peaks/asperities of the concrete and leave adhesive residue in all the texture?

Whats the best thing to wet scrape with?
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Last edited by Jason_Z; 08-05-2020 at 05:44 PM. Reason: more info
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Unread 08-05-2020, 05:39 PM   #7
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Jason, if you read carefully you'll see that, as I mentioned above, they want nothing more than a stain of the cutback residue remaining on the concrete before using the product.
Quote:
Originally Posted by LevelQuik Instructions
LevelQuik instructions"Adhesive residue must be wet scraped to the finished surface of the concrete, leaving only the transparent staining from the glue.
If you're not able to do that, you'll need to go to plan B or take your chances on installing the product over a surface not recommended by the manufacturer.[/url]

My opinion; worth price charged.
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Unread 08-05-2020, 05:48 PM   #8
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This is probably the level I could bring the concrete to... 50% exposed concrete 50% cutback
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Unread 08-05-2020, 06:18 PM   #9
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Without mechanical abrasion I would not tile over that, Jason. YMMV.

I would recommend at least setting one tile over that spot and letting it cure for a week before removal to test the bond. May be OK, may not.

Did you use a razor scraper on that spot?

My opinion; worth price charged.
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Unread 08-05-2020, 06:26 PM   #10
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Hey CX,

That's a good idea, and something I can do now. Once I let the tile cure for a week, what's the test to see if it's good enough? Pop the tile off with a prybar... and if the thinset breaks in the middle instead of at the substrate or tile, we're ok?

I used a small carbide scraper. It was definitely removing concrete... but the cutback was filling low spots that the scraper couldnt get to, which is why you still see cutback. It's wet in the picture which is reason for the color variation.

I guess this begs the question - If concrete isn't polished smooth before cutback, why would manufacturers suggest you could wet scrape to an acceptable level? Is it just a marketing gimmick? What am I missing?
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Unread 08-05-2020, 07:13 PM   #11
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That would be a best case result, Jason, but I expect you'll get something less than that. I'd be looking for a very difficult removal, preferably even on that resulted in a broken tile, but I'd accept just a very difficult removal to make me comfortable doing the entire floor.

If your concrete had been given a "hard trowel" finish, as in quite common in residential SOG work, the razor scraper could be expected to produce the surface the setting materials manufacturers are looking for. I would personally still want to mechanically abrade the surface were it mine.

My opinion; worth price charged.
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Unread 08-05-2020, 07:27 PM   #12
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Yeah, I hear you on that. For such a big job its worth a little extra thought.

I might look into finding some kind of diamond scraper or something with bristles. I should be able to keep it wet pretty easily.

I'll let you know how the tile adhesion test works out in about a week
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Unread 08-06-2020, 08:27 AM   #13
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I found a datasheet for Laticrete 254 Platinum that says suitable substrate "non water soluble cutback adhesive". The datasheet does not mention a wet scraping requirement.

I called Laticrete technical support, and asked about surface preparation and I quote: "you can clean with water and detergent first, but other than that no". I then asked if, like other thinset mortars approved for cutback adhesive, if it would need to be wet scraped first and the reply from Laticrete was "No, you don't need to wet scrape, you would only need to remove the cutback adhesive if it was water soluble because then the thinset would dissolve the adhesive. You do not need to remove the adhesive if it is non water soluble"

https://laticrete.com/tile-and-stone...ct-information

So far the TEC Totalflex seems to be bonding directly to my cutback adhesive.. Will share some pics soon after it has time to cure fully
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Unread 08-24-2020, 08:10 PM   #14
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Natural stone vs tile for basement slab floor?

Hello again,

The area I want to tile is on the basement slab highlighted in blue. I could separate it into 3 sections if it needed CTE joints.

What do people usually use for stone? Are there any special considerations for installing stone on slab vs large format tile on slab?


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Unread 08-24-2020, 08:49 PM   #15
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The critical things on a slab are if there are any cracks. FWIW, a slab generally will, or has already cracked, so that is a critical consideration. If those cracks have elevation differences, you should not try to tile it. If they are expansion cracks, then a crack isolation membrane will likely resolve that problem
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