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Unread 08-25-2020, 06:27 AM   #16
Jason_Z
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no cracks anywhere on the slab, house ~60yrs old
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Unread 08-25-2020, 06:53 AM   #17
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An isolation membrane still isn't a bad idea, and with tile over concrete, unless the floor is heated, a membrane with a thermal break isn't a bad idea either.
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Unread 08-25-2020, 08:21 AM   #18
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I've combined you with your original thread on this floor project, Jason. A moderator can give it a more generic title any time you'd like to suggest one.

What did you decide to do about the cutback on the concrete surface?

What have you decided to do about flattening the floor?
Quote:
Originally Posted by Jason
I could separate it into 3 sections if it needed CTE joints.
What's a CTE joint?

You can use a ceramic tile or natural stone in your application. As Dan pointed out a crack isolation product might provide some additional assurance against cracking of the installation, but is not a requirement. Movement accommodation joints in the tile surface at the perimeter would be mandatory, and, depending upon the size of that floor, at the separations of those areas you've outlined might be a good idea as well.

My opinion; worth price charged.
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Unread 08-26-2020, 03:50 PM   #19
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Thanks for combining

CTE = coefficient of thermal expansion, I assume that's what people are talking about when they talk about expansion joints for tile floors? I'm not sure I'm in alignment with the rest of the community about actually needing them, since the tile is bonded to the floor and not just at the end of each span. But I don't mind adding them in case I don't understand correctly.

I'm thinking of doing a skimcoat with Laticrete 254 and then using self levelling compound over that. The Laticrete rep assured me that 254 can be used directly on cutback adhesive, not just residue, as long as the cutback adhesive isn't water soluble. I tried a modified mortar with some leftover travertine tiles... the joint breaks in the middle of the mortar and the tile is very difficult to remove. The leftover mortar can only be scraped off the cutback adhesive and does not chip off into individual pieces. There is no bond or substrate failure, just mortar failure (TEC Totalflex Universal (modified) Mortar)
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Unread 08-26-2020, 08:13 PM   #20
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does a membrane help if mortaring over cutback adhesive, or not worth the effort even in that case?
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Unread 08-26-2020, 08:27 PM   #21
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When people talk about expansion joints in ceramic tile installations they're nearly always talking about the movement accommodation joints in the tile surface, Jason, and calling everything an expansion joint.

In reality, these joints can be to accommodate actual expansion or construction joints in the substrate as well as control joints in concrete, changes in substrate types or materials, isolation joints, changes of plane in the backing material, etc. There are also the required joints around the perimeter of any tile installation and joints based upon the overall size of the tile installation.

And yes, aside from movements within and between substrate areas, the tile's coefficient of linear thermal expansion is a major factor in the location of joints based upon the size of the tile installation and type of tile.

The industry has specific requirements (EJ-171) for such joints based upon some of the above conditions which formerly had a generic dimension above which a movement accommodation joint was required, but these days there is a more complex formula for such calculations that requires that you know the actual coefficient for the tile in use. I don't know for sure when that change occurred, but nobody asked my opinion. Way more complicated than it was previously and I doubt your average residential setter uses it very often. I suspect it comes up only when there is a failure of a large tile installation and fingers need pointing.

If you're happy with your bond to the cutback as it is, I've got no argument. I'd be more comfortable if your Laticrete rep would point us all to their written instructions about using that 254 (which is known to be good stuff) over cutback adhesive without any abatement at all.

My opinion; worth price charged.
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Unread 08-26-2020, 08:56 PM   #22
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Hi Cx,

That sounds like some good advice on the control joints, I'll have to see if what I have is sufficient for thermal, but no other issues that you mentioned really other than a transition from bare concrete to cutback. If anything, maybe it helps isolate a tile failure to 1/3 the floor? Hoping the design isn't that marginal that this would help.

I agree I was really nervous when starting to read about cutback adhesive and the recommendations on the forum. I admit I'm usually a skeptic and think practical and specific applications can be a bit different... but despite confirmation bias, the test results on my floor look too good. Like, the discount mortar is extremely well bonded to the cutback adhesive and it's hard to argue against. Will the bond weaken over time? Maybe? But will everything be settled by then and it won't be an issue?

The laticrete rep on the phone said "dont need to remove" and I've attached written instructions from their website. I know this might seem a bit pedantic but so far I have no indication that the 254 needs to be wet scraped down to "residue"

thoughts?
Attached Images
  
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Unread 08-26-2020, 09:01 PM   #23
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One thought about the thermal control joints - If there ever was an adhesive failure, the relative motion for a small portion of tiles is probably acceptable (like a pseudo membrane?), but for a large section of tiles might cause visible buckling or separation?

Jason
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Unread 08-27-2020, 04:15 PM   #24
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'Fraid at least one of us is not following your question, Jason.
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Unread 08-28-2020, 09:22 AM   #25
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I would not consider for a moment installing stone over a black solvent based adhesive. You will likely find that the old 9" VAT tile floor breathed a lot more than anything you are proposing. Once that is altered you will have to wait and see what happens after the install. Way too much risk for me.
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Unread 09-03-2020, 05:56 PM   #26
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Hi cx,

Just posted the written instructions that don't recommend removal unless it's water soluable, which they then recommend the removal of. I've been mopping the heck out of this thing to clean the area, and while it does get 'wetted', nothing is dissolving or softening at all.

Im thinking of trying the laticrete 254 skimcoat first, then dropping a 1/2" layer of SLC, and ill have several months of use to observe it before having to do anything else. But eventually I want it sealed and levelled either way. Does that sound reasonable or does it still make it seem like a nervous proposition?
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Unread 09-03-2020, 07:17 PM   #27
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If you'll read the instructions for the SLC you choose, any SLC you choose, I think you'll find the manufacturer does not want it used as a wear surface, even temporarily.

My opinion; worth price charged.
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Unread 09-15-2020, 05:33 PM   #28
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Hi cx,

I just wanted to let you know I found another product that seems like its OK for cutback.

"Ardex Feather Finish". The datasheet says:
https://cdn.ardexamericas.com/wp-con...cal-Data-1.pdf
"Non-water-soluble adhesives should be prepared to a thin, well-bonded residue using the wet-scraping technique as recommended by the Resilient Floor Covering Institute (www.rfci.com) to remove thick areas and adhesive build-up, as well as any areas that are weak or not well bonded to the concrete. Any existing patches below the adhesive must be removed completely."

The RFCI says non soluable cutback adhesive only needs to be taken back to a thin "film" on page 25 here
https://rfci.com/wp-content/uploads/...glish_2018.pdf
"Continue above steps until what remains of the residual asphaltic “cutback” adhesive is a thin, smooth film."
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Unread 09-15-2020, 07:14 PM   #29
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Yeah, same requirements as for thinset mortars, Jason.
Quote:
Originally Posted by CX, Post 2
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.
Once you get it down to that stain, it just doesn't cost much to use an angle grinder and diamond cup wheel to properly prepare the surface.

And I recommend you re-visit post 25. Dave makes his living looking at failed tile installations.

My opinion; worth price charged.
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Unread 09-15-2020, 08:50 PM   #30
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I would assume that 9-inch tile with black adhesive contains asbestos unless proven that it doesn't.

These are always tricky situations. A slab floor that is that big will not be flat enough to install tile over. I'd be inclined to want to self-level over it.

They make bonding primers (like Eco Prim Grip) that will probably go over asbestos glue if you scrape it like you've shown in the photo. Then you could self-level over that.

I would also listen to what Dave said about stone over the black adhesive. Maybe installing a membrane over the self-leveler would help the cause at that point?

No matter what, as a pro, I would talk over this with a product rep and see how they would spec it out. Then follow what they say exactly. There's a lot of risk in this job but if it's your own house then you know what you are getting into.

The movement joints placement looks good to me as long as none of the spans are over 20ft. Usually, you want 1/4 inch, or so, with those joints. That might be tough with natural stone as a lot of it is 1/16th joints.
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