DuRock Over Cut Back, Then SLC? - Flooring - DIY Chatroom Home Improvement Forum

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Old 10-28-2012, 01:05 AM   #1
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DuRock over cut back, then SLC?

I've seen plenty of Q&A's online regarding SLC over top of concrete backer board, but none with the specifics of my situation.
Due to a recent leak from my washing machine I've had to tear out hardwood flooring and plywood subfloor from my den. What I have now is a concrete slab with cut back and tar paper still adhered to the concrete. My intent is to install engineered flooring in this room.
The cut back and tar paper can not be scraped from the concrete. I've tried both a 6' floor scraper, as well as a carbide tipped floor scraper that attaches to a floor polisher. Neither method worked at all.
The slab is not flat, whatsoever. It is up to 2" non-flat (a ridge in the center of the room, which tapers down on either side) I know that I need to level the floor prior to installing the engineered floor, but assuming I don't find a way to remove this cut back and tar paper, what will be the best way to level the surface?
My latest idea is to install DuRock across the entire surface, prime, then SLC over top of that. Then glue the flooring. The reason for the DuRock being that the SLC would certainly not adhere to cut back and tar paper. That said- what should go under the DuRock? Everything I read says mastic is not an option, but it doesn't seem like thinset should be applied over top of the tarpaper either. Any help will be greatly appreciated!


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Old 10-28-2012, 04:46 PM   #2
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Pics of concrete slab

Here are a couple pictures of my concrete floor. The section where you see exposed concrete is where I tried the carbide tipped floor polisher attachment. The blades dulled by the time it had scraped off the cut back from this portion of the floor, and was useless . ANY advice on how to move forward?
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DuRock over cut back, then SLC?-img_1499.jpg   DuRock over cut back, then SLC?-img_1500.jpg  


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Old 10-31-2012, 12:54 PM   #3
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Any Ideas?

I guess the lack of responses on this one confirms what I was fearing-- that this is a 'tough one'.. I made another attempt with my floor scraper only to have the floor laugh in my face. The main issue is I can't get under the tar paper with the scraper edge.

I'm considering renting a gas powered concrete planer to try and scrape the surface. Would it get all gummed up with the tarpaper?

But my original question remains: Can I attach concrete backer board over top of this mess, then SLC over top of that? I know it sounds like covering up one mess with another mess, but I'm really stumped here....

Thanks for any thoughts or different ideas.
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Old 10-31-2012, 01:57 PM   #4
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you don't attach backer board to concrete.

here is the sheet for the quickrete brand of slc


here is another that says it works over cutback


here is the link for the ardex brand installation and tech info

i think all of them required the floor to be free of any loose material and with one you couldn't have any water soluble adhesive on the concrete. all required a primer before pouring the floor leveler.

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Old 10-31-2012, 06:29 PM   #5
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Mapei makes a number of excellent self leveling products as well, and just like the previous poster indicated you'll want to make certain that you use the proper type of primer from the same manufacturer as the leveling compound. There are typically 2 types of primers, one for porous surfaces, and one for non-porous, just make sure you apply it properly and follow the directions to the letter. It also might not hurt to contact the manufacturer directly and see which of their products they would recommend for your situation.

On a side note it seems that the only way to remove tough adhesives from a rough and irregular concrete surface would be to bead blast, chemically strip, or use a large grinder with a heavy gauge wire wheel/disc type attachment. The oil in the tar paper might affect primer adhesion, but going over the cutback won't be an issue, just contact the product maker directly if you cannot find an answer to this potential issue on the primers product data sheet.

Good luck!
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Old 10-31-2012, 06:39 PM   #6
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Jifset is good over cutback ,also---Mix with Linewebers liquid latex and pour and spread----this is good enough---no need for Durrock---just the self leveling compound.
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Old 10-31-2012, 09:56 PM   #7
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You're not going to remove tarpaper and cutback using a wide putty knife or scraper, you need to 'slice' it off using a sharp razor cutting tool if you plan to do it by hand yourself. Although I agree that bead-blasting, shot-blasting or a special grinder or planer is probably a better way to go.

However you may not need to remove all that stuff anyway, if it's all stuck well. There are plenty of products that will work right over that floor as is. But using SLC may not be the best way. Consider the cost of the SLC for starters.

Assuming the perimeter of that room is level but the center peaks 2", you have an average of 1" to fill. We don't know the size of the room, but 1" of SLC is gonna hurt the budget. Tell us the size of the area in question and if the floor along the walls parallel to the ridge are level or not. We may be able to give you an idea how many bags you will need. $$$ ouch.

It might actually be better and cheaper to hire someone to "mud" the floor for you.

To your original idea of installing concrete backer, you already know it's not a good plan at all.

BTW, did you have homeowner's insurance for your home?



TILE GUY - retired- TROY, MI - Method & Product suitability consulting.

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slc durock level cutback

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