Another Cutback Adhesive on slab question! [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Another Cutback Adhesive on slab question!

10-27-2010, 07:46 PM
I've read through a lot of the posts here about cutback on concrete and got some good info, I was just hoping for a little more though! I have a 300 sqft area, the slab is approximately 1953, I pulled off parquet flooring that was stuck down to the slab. I rented a slab grinder and got off what I could, but I am afraid there is too much left over to get a good bond. The grinder seemed to just flatten out a bunch of stuff though it did take off A LOT of material.

My plan was to lay my Warm Wire and then SLC and then tile. But now I am worried for several reasons. I'm not sure I can get a good bond for the SLC, and Watts Radiant tells me not to put the Warm Wire on the cutback for the chance of toxic fumes. They suggest a cork underlayment. So now I am thinking of a good modified thinset suitable over cutback (does that work?), then the cork, then the Warm Wire, SLC and tile. Any thoughts on this method? Or a better method? Thanks for any input!

EDIT: Pics added on the second page.

Sponsored Links

10-27-2010, 08:12 PM
Hi MD, A good modified thinset will stick to the cutback. Check on the bag to make sure it is suitable for going over cutback. :)

10-27-2010, 08:44 PM
Mike, thanks for the reply. What I don't get though is that some of them, Custom's FlexBond for example, says it's suitable for use over cutback, but then within the installation directions, under the slab section, it says:

"Adhesive layers must be removed...Adhesive residue must be wet-scraped to the finished surface of the concrete, leaving only the transparent staining from the glue."

I don't get it!

10-27-2010, 08:47 PM
I think Versabond will stick to it too. You can do a test, thinset a piece of tile down and in a few days (3 to 4) try to pry it up. You want to try to get as much as the black stuff off as possible. :)

10-27-2010, 09:07 PM
The idea MD is for the Tile to stick to the cement rather than the cutback.. That's why CBP's say a transparent film, ya just don't want to try to thinset it to a glob of cutback......:D

Hank B.
10-27-2010, 09:11 PM
The finished surface of the concrete would mean the concrete itself. If you have a 1/32" layer of cutback, your not at the finished surface. once you've scraped down to the concrete your good. You won't get bare concrete unless you grind down past the point where the glue penetrated the concrete. The cutback adhesive stains the floor so it will actually dark even though your at the finished suface.

I scrape off as much as possible, then use ultraflex 2(mapei), Its never let me down and should save you some money over the flexbond.

I believe laticretes primer for their self leveler can be used over cutback but Im not 100% sure. I wouldn't worry about fumes but thats just me.( fumes coming up through the level coat, then thinset, then tile?)

I assume you've soaked an area with water and try to wet scrap to make sure it isn't a mastic and not cutback right?

10-27-2010, 09:22 PM
I understand that they mean the finish layer of concrete, but that makes no sense, if they want you to be at the finish layer of concrete, then why say your product is suitable for use over cutback, when they really want you to have the cutback removed? Know what I mean?!

Hank B.
10-27-2010, 09:30 PM
Because the cutback is still there, staining the surface of the concrete, but you've scraped it all off the surface. If you spill oil on your driveway, but wipe it up, the oil is still there, its just penetrated below the surface. If its no more than a transparent film staining the surface, its still there and your going over cutback, its just not above the surface.:deadhorse

Just scrape it off the best you can, check with Custom Building Products, Mapei, Laticrete etc and find out which one offers a primer that can be used over cutback, roll it on, lay out your warm floor self leveler over it, then lay your tile.

10-27-2010, 10:43 PM
Then according to you there is no difference between a regular thinset and a suitable for use over cutback thinset, because they all say take it down to the film.

10-27-2010, 10:53 PM
something like that MD

Hank B.
10-27-2010, 11:55 PM

The film is still there, so your going over cut back adhesive. I suggested Ultraflex 2 because is can be used over cutback. If the film wasn't there you wouldn't be going over cutback, :deadhorse

10-28-2010, 08:05 AM
Talk about beating a dead horse Hank. Clearly you don't comprehend what I am getting at. ALL the thinsets say that they can go over the film, so according to you, ALL the thinsets are rated for going over cutback. So once again, why do they have specific thinsets that say "suitable for cutback" when according to you they are all suitable?!

10-28-2010, 08:41 AM
MD.. I use Versabond over a surface that I have scraped with a 4" blade alla the time.. I need to get all of the thick cutback off leaving just a "film" of the cutback and have no issues. When thinset mfg's say over cutback, they mean after it has been scraped to a film..

10-28-2010, 09:42 AM
Yeah Mud, I got that. Yet I just got off the phone with Custom, and Laticrete, Custom said film only, BUT Laticrete said with their 253 Gold or 254 Platinum, you can do a skim coat over cutback that is MORE than just a film. Which is what I would consider a thinset "rated for use over cutback". Maybe the others should just change their verbage to "rated for use over cutback RESIDUE"!!

(Which is what I've been getting at Hank)

Houston Remodeler
10-28-2010, 09:45 AM

Now you've learned the magic of our world and how to decipher what is written on the bag. Its best to call techincal support and get the straight poop.

10-28-2010, 09:59 AM
So, I'm fairly confident in going over my cutback area with a skim coat, but let's add another dimension! Part of the slab appears to have been covered with Thoroseal. Great. If I hammer on it pretty hard it will break up, but would take me weeks to do that to the whole area. Any thoughts? The guy at Thoroseal said if it's scarred up enough than you could mortar it...but what does he know!

10-28-2010, 10:01 AM
Yeah Paul, I always call tech support, no matter what project or product I'm doing. The best is when you're in Depot calling the number on the bag and the Depot guy asks if you need any help...uhh no thanks!

Houston Remodeler
10-28-2010, 10:02 AM
We have found it best to limit asking HD employees questions that only start with "Where can I find the...."

10-28-2010, 10:05 AM
I hear that! I'm going to try to throw some pics up here, maybe that will help.

10-28-2010, 10:41 AM
Some Pics. It seems if I skim the top with my hammer drill I can chip all that Throseal off. Going to be a tough job on the joints but I see no other way.

That 747 stuff doesn't do anything, I am pretty positive I've gotten what I can of the cutback up short of spending weeks taking a centimeter off at a time!

Houston Remodeler
10-28-2010, 10:54 AM
Looking good.

We do call this "work" for a reason. If it were easy, I'd be out of a job. :cool:

10-28-2010, 11:12 AM
any other thoughts on my method right now? I am worried about the asbestos possibility, how do you test for that?

Houston Remodeler
10-28-2010, 11:16 AM
A special crew who thinks they work for a TV show comes in and charges you a small fortune before looking through a microscope to tell you if you have asbestos. All the while you've been working there ... breathing...

Someone takes a sample or 3 back to the lab and tests. You get a report. The yellow pages can help you. You really only have to worry if the stuff gets airborne, as from grinding. If you have chunks the danger is far less. Encapsulated asbestos is deemed safe.

10-28-2010, 12:28 PM
Yeah, its mainly chunks, and I'm wearing a respirator, and at this point I'm almost done so...

10-28-2010, 01:27 PM
Well I don't know what to do now. I was going to skm coat the cutback then put the floor heat down and then slc. But Custom tells me you can't put an SLC on a skim coat. Any one have any direction for me?!

Houston Remodeler
10-28-2010, 01:28 PM
use a different thinset ? 800-243-4788 x 235 for laticrete tech support

10-28-2010, 01:46 PM
Laticrete said the same.

Houston Remodeler
10-28-2010, 02:01 PM
Then you are back to a diamond cup grinder and scarifying the top of the ceement.

10-28-2010, 02:10 PM
No I'm good on that front, the reason for the skim coat was to give me a layer between the cutback and the radiant wire. Watts Electric says to not put the wire on the cutback.

10-28-2010, 05:54 PM
The good news MD is that the thinset will adhere to the bare cement very well.. If you have any thickness of cutback it will try to adhere to the cutback as best it can.. If you have thick cutback. it will adhere and hope that the cutback don't separate... The thicker the cutback, the less your chances of adherence.. The thinset will adhere to the cutback, but will the cutback continue to adhere to the floor? :stick:

10-28-2010, 06:47 PM
I feel confident about putting thinset on the floor, what I don't know what to do about is how to get my floor heat in. Watts Radiant says not to put it on the cutback, so I wanted to put a thinset skim coat, then radiant and SLC, but Custom and Laticrete say you can't do SLC on a skim coat, they also say not to do an SLC on a cork underlayment, so what the heck do I do?! Custom's trying to get me to do a floating mortar bed, which I have no idea how to do, I think he just wanted me to buy more Custom products as he named about 8 different ones needed while explaining how to do it!

This is where the floor is at after cleaning it all I possibly can. What to do from here I don't know.

I'm starting to think that I just scrap the idea of using an SLC all together. The floor is pretty flat, and mostly level, my main reason for using the SLC was to encapsulate the radiant so I wouldn't have to tile right over it, but I guess it's not an option. So if I do a skim coat of thinset just to have a break from the cutback to the radiant, then I can just lay the radiant and tile right to the skimcoat?

Houston Remodeler
10-28-2010, 09:38 PM
Come on guys, someone has to have an idea for this guy. I don't run into much cutback so I'm out of ideas :shrug:

10-28-2010, 10:18 PM
I don't run into any either. Like I said before buy a bag of Versabond and set a piece and in a few days try to pry it up. Only thing you will be out is 15 bucks. :)

10-28-2010, 11:09 PM
Paul, thanks for trying to get me some help!

Mike, doing a test tile doesn't really help me as I'm not trying to set the tile to the slab, I have to figure out how to get the Warm Wire in first.

To add yet another issue, it seems that most people around these forums think that an insulating layer is necessary over a slab with a radiant system. I'm not trying to heat the room or anything, just get the tiles toasty. Do I need an insulating layer? If so, what? Most of the radiant places say cork but I don't like the idea of that at all. I am thinking if I have to do it it would be Noble CIS or Easy Mat I guess. And then we are back to how well I can bond an insulating layer to the cutback residue. UGH!!

10-28-2010, 11:39 PM
MD you could go the extra step and install a thermal break. Easy mat would work and also Kerdiboard would too. You could get some Laticrete 254 and skim coat the whole floor then do whatever. :)

10-29-2010, 12:13 AM
Yeah I guess I'm leaning toward Easy Mat, mainly cause it's easily accessible and I need to get rocking on this by saturday! I suppose that whatever bond I'm going to get with the shape the slab is in is going to be the same whether I use an underlayment or not right?

10-29-2010, 12:26 AM
Right. If you bond the Easy mat you can easily do SLC over it with your heat wires. :)

10-29-2010, 08:19 AM
Custom says to definitely NOT put SLC on Easy Mat. They say it is too thin and brittle and Easy Mat is spongy. They've told me this on two different phone calls. Anyone know more about the Noble CIS? I think I can get that easily too.

10-29-2010, 09:52 AM
I'm trying to decide whether or not to even use an insulating membrane on my slab before installing electric radiant and tile. I am in Maryland, the slab is about 4 feet below grade. Is it necessary to use an insulating membrane? If so, what? All the radiant companies say cork, Acousticork being one of the good ones engineered for the tile industry and backed by the TCNA. I'm also trying to find something readily accessible, I've seen Easy Mat around too, doesn't look that great to me. Any thoughts?

Brian in San Diego
10-29-2010, 10:35 AM

Please ask all questions regarding this project on this thread. We employ a "one project, one thread" policy so we have all the background information on one thread. Makes it easier for us to keep track of everyone's project.


10-29-2010, 10:45 AM
I once cleaned glue that was used to adhere linoleum to a basement slab with a sandblaster ( a real one...not a siphon blaster). The silica sand made a mess but it got the glue off....walnut husks may be a better blasting agent to use....Steve

10-29-2010, 02:22 PM

re: EasyMat. Didn't you just answer your own question in the (now) immediately prior post? :scratch:

10-29-2010, 07:42 PM
Umm, I don't believe I did. I said earlier that I've decided to scrap the idea of using an SLC. So at this point I am just trying to figure out what thermal break to use, and if I even need one to begin with.

Brian, I understand your point, but at this point, the title of my post is about the cutback adhesive, and I have solved that issue, now I am trying to get input as to whether or not I need a thermal break and if so what kind to use. I started a new post thinking that people might want to weigh in on that topic, and might not want to weigh in on the cutback topic. In other words, the cutback post title is no longer relevant to the information I am trying to gather, nor is most of what else is written therein.

10-29-2010, 07:45 PM
Axe a Mod and you shall have your wish.. ;)

10-29-2010, 07:51 PM
Hmm, ok sorry I misread. You're gonna bed the heating mat/cables in thinset then?

10-29-2010, 08:01 PM
MD, we can change the title of your thread to something more generic any time you'd like to suggest one. :)

But we'd like you to keep all your project questions on a single thread so folks can see what you're working on and what's been previously asked and answered.

As to the cutback issue, I'm not seeing where that was resolved. You just planning to tile over what we see there in your last photo?

The issue of the cleanliness of your floor doesn't change at all because you decide to use, or not to use, a thermal barrier of some sort over it. Anything you elect to attach to the slab with thinset mortar is gonna have the same problems if the slab is not properly prepared.

The issue of the thermal break has been discussed here dozens and dozens of times. Type thermal into the Advanced Search, ask for Titles, and you'll get a few threads to get you started. Couple of them lead to other threads.

Bottom line remains: Depends upon who you axe, eh?

Cork is one of the oldest materials used for crack isolation, uncoupling, sound attenuation, thermal insolation, and who knows what all for tile installations. It excels at being not really very good at any of'em.

There are other underlayments that are more useful for the thermal isolation and do the job better than cork but are still less than wonderful. They help, of course, but the actual benefit is much disputed.

Up to you. Your house, your floor, your tile, your dinero, your call.

My opinion; worth price charged.

10-31-2010, 12:22 AM
CX, sorry, I should have posted an updated photo, here is the floor as it sits now, pretty clean after two days of chipping off thoroseal, and good to go. By the same token, I assumed people understood that the cutback issue was resolved after several of my posts including:

"So, I'm fairly confident in going over my cutback area with a skim coat"

"No I'm good on that front, the reason for the skim coat was to give me a layer between the cutback and the radiant wire."


"I feel confident about putting thinset on the floor, what I don't know what to do about is how to get my floor heat in."

This is exactly what I am talking about as to why I started a new thread. My need for information NOW is about thermal breaks, and which, if any, I should use. Anyone reading this entire 4 page thread, such as Paul, would be with me on the progress being made. But hardly anyone reads the whole thread to understand the progress of the job to date, including yourself or you would've seen where I moved on from the cutback issue, to asking for information about thermal breaks. You only deemed it necessary to give any input when I replied to Brian about adding a new thread. Furthermore, I did do an advanced search using the key word "thermal" as you suggest and 9 threads come up, 1 from '09 which is discussing Ditra, another from '09 with zero information and 1 from 2010 has one reply, from yourself, telling the person to do an advanced search. There are 6 more, 5 of which are pre-2006, I am assuming that some things have changed in the past 4 years such as newer products and was looking for some information a little more current, as well as a little more customized to my situation, which is why I stated that I am in Maryland, with a slab 4 feet below grade. I don't know where the frost line is. The final thread from 2010 has the exact question I have, written by 'gitchi gummi' (Mark)

"Tile experts, please tell us acceptable ways to insulate under our tile and above our slabs."

To which you answer, "Mark, will you please visit the FAQ page (link in the dark blue bar near the top of the page) and find the part about attributing quotations. It's very distracting to see a list of quotes in a thread and have no idea who's being quoted, eh?"

I've found a bunch of stuff about insulating slabs from radiant, people throw around names of products left and right, but I have yet to find any info on WHY a product does or doesn't work. You say cork doesn't do anything well, WHY? And why is it pushed by TCNA and all the radiant companies? I am asking in earnest, WHY? All I'm trying to solicit is some information as to whether people think I need a thermal break to begin with and if so which ones are good and/or bad and why? Sorry that I broke your protocol.