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Old 06-07-2010, 11:48 AM   #1
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Crack in Concrete Subfloor - options?

Hi all - I've been lurking here a bit since buying my first home at the end of April and am moving full steam ahead with all of the projects I have to do. The next (and last!) major project is flooring. We had wanted to put porcelain tile down in each bath (there are 2) and the kitchen but I've hit a snag.

When I removed the existing flooring in bath #1, I noticed a patch job in the concrete slab foundation. It looks like they had to get in to the foundation, possibly to fix some plumbing issue at some point (I'm not sure exactly). So aside from the patch job, there's a good sized crack as well. Here are pictures of what I found:

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So - I filled the crack and now it looks like this:

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Above you can see the 'patch job' that was done previously.

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The area where you can see the patch job is somewhat uneven so regardless of what I put down I'll have to level the floor a bit (my project tonight). The crack SEEMS to be the result of whatever work was done when the patch was created but it still have me nervous if I were to lay down tile.

Is what you see here enough reason to scrap the idea of putting tile down and go with another flooring product or does it not seem too risky if I make sure everything is flat and I use a membrane over the cracked area (3 times the width of the tile, of course)?

You can see the glue on the concrete from something they had there before, but the concrete itself is quite rough so I'm thinking that I don't have to sand that off before using the self leveler tonight.

Thanks in advance for the advice - I greatly appreciate it. In related news, that bath is off of the kitchen and the patch job extends in to the kitchen a bit, so I've decided to put a floating floor in the kitchen.
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Old 06-07-2010, 12:24 PM   #2
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Bill, if there is any vertical displacement of the slab from one side of the crack to the other, you can probably rule tile out. Vertical displacement may be a difference of height or it could be a change in slope. If there is no vertical displacement, then an antifracture membrane can be used.

If you have the height, a floating reinforced mud bed could allow you to use tile, but that makes for a almost 2" step up into the bathroom.
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Old 06-07-2010, 02:19 PM   #3
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Thanks Bob - there seems to be very little vertical movement over the majority of the area where the crack is. When I place a level over it, it's flat on both sides for the most of the length of the crack. There are a couple of areas where that's not the case, but the difference is pretty small. I can measure tonight if that would help. Of course the area where the patch job is is fairly uneven, but that's due to a crappy patch job.

I'm not sure that I'm in love with a floating reinforced mud bed due to the height differential and the amount of work involved when I've got 3 other rooms to do flooring in (one more bath with tile, hopefully and the kitchen and living room with a click lock floating floor).

I'm going to level the floor tonight then hopefully decide what to do about the floor by Friday since I took it off in anticipation of being able to lay some kind of flooring down.
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Old 06-07-2010, 03:46 PM   #4
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Shouldn't be a big problem from what you write. Put some Redguard over it and tile away.

"Women and cats will do as they please, and men and dogs should relax and get used to the idea."
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Old 06-07-2010, 04:20 PM   #5
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Welcome, Bill.

I can certainly agree with what Bob said about your cracking issue. The "repair" you show there will certainly fill the crack, but it doesn't really do anything to prevent future cracking nor the old crack from opening again. Or trying to close.

Not trying to discourage your SLC experiment, but you do understand that your tile doesn't need a level surface at all, it only wants it to be flat. And if you require a good bit of flattening because of your cracked areas, I think you have a pretty real problem for a ceramic tile installation.

Can't share Laz' enthusiasm for just putting down a little RedGard and tiling. That floor looks bad enough to me that I might tile it if it were mine, but not for a customer. And if I were to tile it I'd want a pretty serious crack isolation membrane such as Nobleseal CIS or similar.

My opinion; worth price charged.

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Old 06-08-2010, 10:01 AM   #6
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Thanks for the advice, everyone.

Yes, I understand that we're going for flat, not level but using a leveling product seems to be the quickest, easiest way to get the room flat. The cracked area is generally flat, but the patch job area is a bit on the bumpy side which is why I thought it best to use the leveling product so the room would be uniformly flat.

I'm still torn as to what to do. I'm not the kind of person who asks for advice and does what I want to do anyway. I've seen that happen quite a bit in these forums and it's annoying and frustrating! If I talk myself in to taking a chance with the tile it'll be because it's only 35 square feet and I need to do another bathroom anyway (or will I once I discover what's under the current flooring there?!) so I might as well get some practice in with this room.

Of course the other factor is that talking the girlfriend in to not having tile hasn't been easy (of course, she isn't the one doing the initial work or the repair/replacement if there's an issue!). Any suggestions on other good looking products that we could use instead of tile? I found some decent looking click lock flooring that looks like tile in the local big box hardware store but I'm a bit nervous to use that in a bathroom even if it is supposed to be moisture resistant.
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Old 06-08-2010, 11:35 AM   #7
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Bill, you can level the floor with SLC, but you still need the membrane. Put the membrane on top of the SLC. If the crack moves again, the SLC will crack, but the membrane will provide some protection for the tile.

Rent or buy a angle grinder and a diamond cup wheel to remove all that yellow stuff, level the area that was repaired, and get down to decent concrete. Install the SLC according to the manufacturer's instructions. Dam the threshold and any other leak paths, including the toilet flange. Plan your pour to have about 1/8" to 1/4" over the top of the high point. Alternatively, use the cup wheel to knock the high points down so there is no more than 1/8" variation in height across the room., and skip the SLC.
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