DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Tiling, ceramics, marble (
-   -   How to properly fill stress cuts in concrete before tiling? (

vseven 04-19-2011 06:11 PM

How to properly fill stress cuts in concrete before tiling?
I've decided to tile my unfinished basement instead of carpeting. There is about 1000 sq/f total and the basement currently has stress cuts in going lengthwise side to side and three more front to back. The level of the concrete on each side of the cuts is pretty close, within about 1/32" of each other except for one perticuliar spot near a wall that's closer to 1/16". Either way I'm fairly confident I can set it at the right heights especially after doing a small 50 sq/f bathroom already and learning a thing or two.

My question is on the stress cuts. The narrowest one is around 1/8" and the widest is closer to 3/8". I was told I should fill them then put a "membrane paint"? over the crack about a foot to each side? First question is what do I use to fill the cuts? Secondly what do I use to paint over each side? Lastly should I use some foam 1/4" backer rod in each cut before filling them? They drop in about 3 - 4" to the gravel underneath and I'd hate to waste a bunch of material down each cut when backer rod is 5 cents a foot in bulk.

Bud Cline 04-19-2011 07:18 PM

That floor is not suitable for ceramic tile.:)

vseven 04-19-2011 07:40 PM

It sure is....I've had numerous people look at it and say it's fine for directly laying with thin set including getting two quotes on the work (which both were a bit high I thought). Other then the stress cuts it's perfectly flat and smooth.

Bud Cline 04-19-2011 07:57 PM


Other then the stress cuts it's perfectly flat and smooth.
That's not what you said an hour ago.
Here's what you said:

The level of the concrete on each side of the cuts is pretty close within about 1/32" of each other
"pretty close" is not "perfectly flat and smooth".
Then you went on to say:


except for one perticuliar spot near a wall that's closer to 1/16".
Now which is it?:)

If the floor has cracks and those cracks are higher on one side of the crack than on the other side of the same crack that floor has a tendency to heave and it IS NOT suitable for a rigid tile installation.

Those bidders are trying to sell you a pig in a poke. Just try to find them to stand behind that installation when that floor begins to crack and heave with seasonal changes.

You are getting some bad information, now that someone (someone being me) has told you the truth you don't want to see the possibilities and risks you are taking with a thousand square feet of tile.:):no:

vseven 04-19-2011 08:23 PM

Of the two that quoted me the one I've seen his work and I couldn't find any faults with it. I asked him about the height difference of 1/32" and he said it's nothing to be concerned about. I asked about the one section of 1/16" (it's about 3 Sq/f of floor against a wall) and he said again it's nothing to worry about. So I'm not worried about it....the floor has been set for 12+ years.

Thanks for your input but I'll trust the word of people that have seen the floor. I'll look for the answer to my question on google and hope it's as accurate as this site since questioning what I'm doing is more important then answering a question.

Bud Cline 04-19-2011 08:31 PM

Not questioning what you are doing as much as trying to save your butt from self destruction. Of course you can do what you want to do. I've given you some straight poop based on thirty-five years in the tile installation business and have nothing to gain or lose from it. Those guys have a project to sell to you. Mark-my-words my friend: That floor is not suitable for a rigid ceramic tile installation. There are none so blind as those that will not see!:)

There is no reason for you to get pissed now.:) You'll have plenty of time for that later.:)

Give it some time and let some others chime in here and see what the consensus is.:)

vseven 04-19-2011 08:56 PM

I will use the backer rod idea along with caulk to "seal" the stress/tension cuts but still allow them a slight amount of flex.

The floor meets everything I've read for the porcelain tiles I'm look at (18x18), it absorbs water if you put it on (doesn't puddle...gets absorbed quickly), it's smooth in very large chunks. The smallest "chunk" between cuts is around 160 sq/ft and as mentioned the height difference between every section is less then 1/32" except for the one odd ball part (and that part is low 1/16" which is why I was told by both installers that they would just add a bit more thinset and I would never notice it).

I believe what I want for both sides of the cuts is "Laticrete Blue 92", both installers said they would use a paint on membrane for each side going 1 to 1 1/2 feet from the crack.

If I have to I can attempt to level the 1/32" out but I don't see how I would really be adding anything to the low side that wouldn't be made up by the thinset by itself.

Bud Cline 04-19-2011 09:10 PM

The Blue 92 should be spread 1-2 TILES beyond each crack.

The Blue 92 should be trowelled on with a notched trowel, NOT painted on with a roller or a brush. Trowelling with a notched trowel will provide the required "mil thickness" for the 92 to work properly. Painting it on or rolling it on will not provide the proper mil thickness.

The larger the tiles the flatter the floor must be. Eighteen inch tiles are large tiles. Concrete floors are notorious for being out-of-plain over a large area. The floor is not as flat as you think it is.:)

Lippage will be a serious issue and some type of levelling system should be used, Tuscan is the best for this type of project.

A flexible thinset should also be used, something such as Custom Building Products Mega Flex.

The above products, ie; Blue 92 and Mega Flex are to mitigate possible damage from lateral movement. NOTHING will stop the upward movement of a heaving slab from cracking ceramic floor tiles.:)

firehawkmph 04-19-2011 09:18 PM

I think what Bud is trying to tell you is this: It's not so much the slight difference in the joints right NOW, it's what happens down the road if either of those slabs move up or down. I just ran into this on a basement job. I talked to the tile reps at the warehouse where I buy my tile, checked my tile bible book, and they both agreed with each other. The only proper way to tile over a control joint it to create a control joint between the tile right over the control joint in the cement. So basically the tile on one side of the joint is independent of the other side. Normally the cut joints in the cement are not where your tile layout wants them to be. And in your case, the larger the tile, the more susceptable to movement and a floor not being flat they are. I have to agree with Bud, the tile may go down and look good for now, but I would bet money it won't last without cracking.
Mike Hawkins:)

JazMan 04-19-2011 09:38 PM

Hi Guys,

Bud has given very sound info and suggestions for this installation. The horizontal cut/crack movement is fairly easy to deal with. The products mentioned, applied per directions along with properly place expansion joints in the tilework and perimeter will help prevent future problems due to lateral movement. (shrinkage or expansion of the slab, yes it will do that). The problem comes from up and down movement from heaving or drooping of either side of the slab.

The only way I know to save the floor from damage due to vertical movement is to install expansion joints in the tilework directly above the cuts. These joints must be at least as wide as the grout joint, but NEVER less than 1/4" wide. Wider in damp/wet areas, sunny areas, and when the temperature variations meets a certain limit. (not likely the case here).

So, now you know there may be a problem. I know you really want tile on that floor, and we do too cuz it's the best flooring on the face of the earth. Make sure you buy and keep extras.


vseven 04-22-2011 12:58 PM

Sorry if I came off flippant, I didn't mean to. I just know multiple people (both the two professionals with tiling companies older then me and casual do-it-yourself tilers) have seen my basement and all of them have said the exact same thing. So I have to trust what everyone who has seen my situation says.

With that said a little background. The house was built in 1999, walls are ICF (concrete filled). Floor is smooth trowled with stress cuts as mentioned (that end a few inches from the walls). The one side had some water coming in but it was due to the previous owner building a stone patio the year before I bought the house that was too tall and was pooling water to the point of going "over" the poured foundation (up under the siding and between the concrete and rim joist). I fixed that issue and it's been pretty dry until early last month. The area had a weird couple days where the ground was fully saturated, there was snow on the ground, and a huge thunderstorm came through. Both my utility and toilet drain (no toilet yet) in the basement started back feeding storm water (thankfully it was 99% clear water with some silt...smelled like decaying leaves) and we ended up with about 6 inches in the basement.

I talked to the sewer department who came out that morning and pretty much said they have never seen this much water in the system ever in there time working for the village and houses all over the area are flooding. I talked to the previous owner and asked about flooding and they said it never had happened before. I then checked with neighbors and it was year one house did it and the others were fine, another year a different house did it and the others were fine (were in a small 11 lot "development"). Looks like it was just my houses turn. I have been working on finishing the basement for over a year now (Re: and thankfully nothing was ruined. I got the water out (thank you walkout basement with big sliding door) and the drains stopped back feeding about three hours after they started. A couple shop vacs, couple dehumidifiers, and a very long 14 hour day and the basement was fine with no real damage other then some mudded joints near the floor that started to suck in which will be covered with base molding.

So now I want to do tile because I don't want to have to go through ripping out carpet in the very slim chance it happens again. I had just finished tiling and sealing my 50 sq/ft bathroom down there and it was a breeze to clean after the vac, quick mop, and done ten minutes later. All the water just beaded up on the surface and none of the black silt got into anything because of the sealing. The bare concrete however took all day with shop vacuuming, scrubbing, rinsing off, sucking it back up, then finally running a carpet cleaner over it to get whatever was left (which it turned out was a lot).

With that said I will put tile down either myself or hire someone to do the actual tiling portion and I'll do all the prep. so anything anyone can suggest to "minimize" problems would be great. I plan on buying a extra 50 sq/ft of tile for backup if the floor does move and in case something breaks. The tiles I'm going with will be 18" x 18" and installed in a diamond formation. I've been doing more reading and I'm thinking of sealing the stress cuts the same way I thought about (backer rod and flexible caulk) then I'm going to fill in the one low spot (the 1/16" one) with a self leveling thinset material so I don't have to purposly add extra thin set during install. Lastly I'm wondering if it would be worth coating the entire floor with something like RedGard and using it as a crack prevention membrane. The cost would be around $250 for the entire basement, half that to do all the stress cuts and the recommended distance on each side of them (which is the diagonal length of the tile so 25.5" on each side). Anything else I can do?

JazMan 04-22-2011 07:58 PM

The small areas that is a little low is easy to level as you mentioned. Not a problem with that. I'm not as satisfied with your other plans.


I'm thinking of sealing the stress cuts the same way I thought about (backer rod and flexible caulk)
That's fine, that's essentially the short form way of treating a control joint. But, the same control joint should continue in the tile work. I haven't heard you say you realize that yet.


Lastly I'm wondering if it would be worth coating the entire floor with something like RedGard and using it as a crack prevention membrane. The cost would be around $250 for the entire basement,
$250 to coat 1,000 ft? I don't think so. You'll need at least three 3 1/2" pails I think.


vseven 04-22-2011 09:08 PM

Yeah, looks as though I would need more then two but not quite three (although I guess it wouldn't hurt to put it down slightly heavier).

JazMan 04-22-2011 10:48 PM

Ok, answer the easy one. Disregard the important steps. Maybe they'll go away?


vseven 04-23-2011 08:20 AM

4 Attachment(s)
I went down with a square and checked all the stress cuts, out of the 7 I'm dealing with 5 are level, one is 1/32" (actually closer to 1/64"), and the one as mentioned is a little under 1/16 that I will be filling.

If after 12 years I have less then a 1/32" height difference between each piece then yes I am going to ignore it. Shouldn't I?

All times are GMT -5. The time now is 01:53 PM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1