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Old 03-15-2012, 08:47 AM   #1
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


I'm looking to tile the basement, and I'm wondering if using an uncoupling underlayment on top of the concrete slab is necessary/strongly recommended or optional? I've read and some folks say "just tile over it," but some folks recommend the underlayment. I was curious what the experts think here is the proper way to do it.

The house was built in 1985, and I haven't yet ripped up all the carpet (and vinyl underneath the carpet) to prep the slab, but it looks good from the exposed part I see (no big cracks/etc). I understand I'll need to clean it thoroughly and may need to use some SLC to get things level, but that's another topic. Thanks for anyone's input!

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Old 03-15-2012, 09:26 AM   #2
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


Using something like Ditra helps with small cracks but is not really a crack isolation membrane.

A product like Noble Company's Noble Seal TS will give you crack isolation and help warm the floor a hair.

In my basement I'm playing around with 1/4" cork which I installed with modified thin set. The cork is amazing and the room no longer cold.

How large is the room? God places a crack every 10' whether you want it or not!

JW

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Old 03-15-2012, 09:45 AM   #3
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


Thanks John for the info and response. The space is roughly 19'x19' + a small hallway about 4' x 8' or so. Here's a picture of the space currently. It's a townhouse. Interesting idea with the cork.. Only concern I have is durability. In case there's a leak/etc. in the basement (it's a walk out in the back, so it's not very humid/moist), I'd be concerned about mold developing under the tile. I considered doing some kind of heated floor underneath the tile, but opted it's not worth the cost (for us). Large area rugs will have to suffice in the winter. My main concern is really crack prevention/longevity.

So in your last sentence, is it safe to assume then that avoiding cracks is impossible regardless of whether I use an isolation membrane or not? Or perhaps using "control joints" (if that's the correct term) every 10' would work? Thanks for the input!

-Mike
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Old 03-15-2012, 08:55 PM   #4
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


Typically, you look at the concrete and use some isolation membrane if there are cracks. You have to also look at the age of the basement and the condition of the cracks. If the basement is from 1985, it may be done cracking. If the cracks are protruding up 1/2" from each other, you won't be able to tile anyway.

You also want to look at where the control joints are, if there are any. I like to saw control joints where walls will be placed, then you can put a control joint in the tile when you do the door threshold.
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Old 03-16-2012, 10:45 AM   #5
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


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Typically, you look at the concrete and use some isolation membrane if there are cracks. You have to also look at the age of the basement and the condition of the cracks. If the basement is from 1985, it may be done cracking. If the cracks are protruding up 1/2" from each other, you won't be able to tile anyway.

You also want to look at where the control joints are, if there are any. I like to saw control joints where walls will be placed, then you can put a control joint in the tile when you do the door threshold.
So if there are just smallish cracks, can I just tile right over the slab without an isolation membrane? Seeing as how the house is 25+ yrs old, I would imagine any settling cracks will have run their course, but wasn't sure what I needed to do to prevent any future cracking.

If there are large cracks protruding up, can I just grind it down so that it's level? Thanks.
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Old 03-16-2012, 12:53 PM   #6
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


I would say if there are hairline cracks, I would contact an isolation membrane manufacturer and ask them how far out to go with the membrane. I suspect if it is sold in 4' widths, they would be able to tell you if you need to come out from the crack 2' in each direction, or 1' in each direction.

If it is a bigger crack with a lip on it, I would re-think tiling it. I guess your options are grinding the floor, filling with a leveler, or removing and replacing the floor. My concern with grinding or filling is that if the floor has moved up and down, what will stop it from doing the same again?

I only have experience laying tile on a "modern" slab with 4" of rock or sand underneath, control joints, etc.

There is a large, recently constructed shopping mall nearby, and there was a lot of tile laid on the slab. I think it is 3 years old. I noticed that there are many cracks developing every 12 feet or so, that run all the way through a walkway running down the center of a store. There is carpeting on either side, and I suppose the crack continues there.
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Old 03-16-2012, 01:26 PM   #7
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


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I would say if there are hairline cracks, I would contact an isolation membrane manufacturer and ask them how far out to go with the membrane. I suspect if it is sold in 4' widths, they would be able to tell you if you need to come out from the crack 2' in each direction, or 1' in each direction.

If it is a bigger crack with a lip on it, I would re-think tiling it. I guess your options are grinding the floor, filling with a leveler, or removing and replacing the floor. My concern with grinding or filling is that if the floor has moved up and down, what will stop it from doing the same again?

I only have experience laying tile on a "modern" slab with 4" of rock or sand underneath, control joints, etc.

There is a large, recently constructed shopping mall nearby, and there was a lot of tile laid on the slab. I think it is 3 years old. I noticed that there are many cracks developing every 12 feet or so, that run all the way through a walkway running down the center of a store. There is carpeting on either side, and I suppose the crack continues there.
Thanks again for the response and info. I hadn't really thought about that (with big cracks), but that makes a lot of sense. If the slab is moving at all, I guess any tiled surface would certainly crack over time. I guess I'll have to rip up the floor and take a look. On the exposed section of slab (the laundry room and the small section of the larger room) I don't recall seeing any noticeable cracks, so that's a good thing.

If there aren't hairline cracks, is tiling directly on top of the slab a-ok, or should I always use an uncoupling membrane?

-Mike
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Old 03-16-2012, 06:24 PM   #8
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


It is OK to tile over it if there are no cracks. If it has been there for a few years, I would go with it. Cracks that I have seen form have happened either overnight because I didn't have expansion joint against an inside appendage (recessed entry) or over a set of seasons. So if it has been one year, I say go with it.
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Old 03-26-2012, 08:58 AM   #9
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


Last question for you guys.. Will using something like ditra as an underlayment actually help the tile floor not be as cold, or is it purely an isolation membrane to prevent cracking? Someone was telling me it helps keep the floor warmer (rather than tiling straight to the slab), but I'm skeptical that it actually helps keep the tile warmer, since the ditra is set in thinset, and tile is set in thinset on top of the ditra. Anyone care to comment if ditra helps keep a basement floor a little warmer? Thanks!
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Old 03-26-2012, 08:33 PM   #10
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


That Ditra under the floor will not only warm the tile, it will make you better looking and your investments will start doing better as well.

Your flatulence problem will cease and your spouse will love you more.

You might want to consider a double-layer.
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Old 03-27-2012, 07:46 AM   #11
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


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That Ditra under the floor will not only warm the tile, it will make you better looking and your investments will start doing better as well.

Your flatulence problem will cease and your spouse will love you more.

You might want to consider a double-layer.
Forgive me if I missed the clear answer in all the sarcasm.. So ditra won't make any difference? Thanks.
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Old 03-27-2012, 08:26 AM   #12
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


More sarcasm then answers when it comes to flooring and tile here.....

One half dozen or the other for ditra on concrete it still needs to be placed in thinset the call is yours I think anyway.
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Old 03-27-2012, 08:37 AM   #13
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


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More sarcasm then answers when it comes to flooring and tile here.....

One half dozen or the other for ditra on concrete it still needs to be placed in thinset the call is yours I think anyway.
Thanks Jetswet.. My latest question though is does ditra provide any insulating properties? Does it make the tile less cold because there's a layer in between the tile and the slab w/ the ditra?
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Old 03-27-2012, 08:44 AM   #14
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Tiling basement on concrete slab- Use uncoupling underlayment or not?


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Thanks Jetswet.. My latest question though is does ditra provide any insulating properties? Does it make the tile less cold because there's a layer in between the tile and the slab w/ the ditra?
http://www.schluter.com/media/DitraHandbook.pdf

Forgot what page 13 I think. But yes your tile will take the room temp before it takes the slab temp.

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