Crack treatment

[BillBo]

The crack in the attached pic is at an inside/outside corner of the concrete. The concrete itself is about 40 years old and part of the above-grade floor that supports living room and garage and sits (a second pouring) on the below-grade concrete of the basement. I noticed the crack from the outside when we moved in, assumed it to be outside only, and "fixed" it back then with some spray-in foam insulation; was surprised to find it inside as well.

I sent sample of the tile and the mastic to a lab for asbestos testing and will properly remove those before I set tile.

My question for you guys is, once I've prepared the floor, how would you fix the crack. As you can see (well, or not), it's up to 2 inch wide, more than 20 long and VERY deep (almost 30 inch or so where you can see it at one (but not the other) of the outside walls.

Also, would you remove some of the drywall to check whether the outside wall is still properly supported in that corner?

[cx]

Welcome, Bernd.

Let me make a couple assumptions here and you correct them if I'm wrong.

Since we're a ceramic tile and stone information website, I presume you intend to install tile over this concrete floor.

By your description I'm assuming that your concrete floor is sitting on the poured concrete or CMU (block) walls of a basement and is spanning, unsupported, that basement area.

If so, we'll need to know more about your slab.

As to fixing the crack, I'd make no attempt to do so. Not likely to work and will serve no practical purpose. You can fill it if you like, but you'll always hafta treat it as a crack on accounta it'll always be.........a crack.

If my assumptions are not correct, we can discuss the situation a bit more, but you'll still have a crack in your concrete.

I suspect that crack almost certainly has a vertical component, i.e., one side of it is a little higher than the other. Is that correct?

Let's stop there and see if we're on the same page or even in the same book, eh?

My opinion; worth price charged.

[BillBo]

> I presume you intend to install tile over this concrete floor.
Yes (and I said so ;-)

> By your description I'm assuming <SNIP>
Not quite, sorry if haven't been clearer. Just assume it's a separate slab of poured concrete above grade.

> it'll always be.........a crack.
Sure, understood, but this doesn't mean I'll ignore it.

[cx]

OK, then, let me presume you intend to lay ceramic tile on your slab.

We really need to know as much as you can tell us about that slab, Bernd. Above grade concrete slabs don't act the same as SOG, especially if part of it is for parking of automobiles as it appears from your description. You can have a good deal of deflection going on with that arrangement.

How 'bout the vertical component of the crack?

And if you'll visit our FAQ near the top of the page you'll find a brief tutorial on how to post and attribute quotes here on the site. Very simple once you see it.

[BillBo]

Originally Posted by CX

OK, then, let me presume you intend to lay ceramic tile on your slab.

Yes, please do, after all it's what brought me here ;-).

Originally Posted by CX

We really need to know as much as you can tell us about that slab

Oh, well, I shall try then. So, assume 2/3 of the house rests on below-grade slab (with a below-grade basement), while 1/3 of the house (living room and garage) rest on above grade slab (which is still SOG as I understand the meaning of SOG, ie, concrete slab resting directly on the ground). It's one house, though (eg, steel beam running full length through it), and the concrete is connected but doesn't seem to have been poured at the same time. I'll check again tomorrow, try to be more precise, and to make some additional pics.

Originally Posted by CX

How 'bout the vertical component of the crack?

As I said, pretty deep. I can provide a pic tomorrow.

[cx]

Depth is of no concern in the crack, Bernd, we need to know if one side is higher than the other. At all. Even a very little bit. That's what I mean by vertical component.

[BillBo]

Originally Posted by CX

we need to know if one side is higher than the other

Thx for the clarification, CX. The answer is yes, the corner dropped by about 1/8, evenly in all directions.

I also attach another pic to clarify, and partially correct, an earlier statement, namely, that the poured concrete sits on top of another layer of concrete. Hope this helps to get a better idea what I've got.

[cx]

'Fraid that photo doesn't tell me a thing, Bernd. I presume that's the exterior of your foundation? But I see no crack.

The vertical component of that crack on the inside means you haven't got a prayer of successfully tiling over that area unless you are willing to provide a movement accommodation joint in your tile surface that mirrors that crack.

And you'd need to expect that whatever seasonal movement (or continued structural failure) you have in the slab would be telegraphed directly into the tile surface. Corner goes down, tile corner goes down with it, etc.

My opinion; worth price charged.

[BillBo]

Thx, CX, for you continued concern.

Originally Posted by CX

'Fraid that photo doesn't tell me a thing

You said you need to know everything about the concrete (whether it's SOG or not) so I provided you with a pic that tells the outside story.

Originally Posted by CX

whatever seasonal movement <SNIP> would be telegraphed directly into the tile surface.

I didn't expect anything else and am going to use a de-coupling membrane to hopefully prevent the worst

So, back to my original question: what material would you guys use to fill the crack?

[Davy]

If you're going to go ahead and tile away and hope for the best, fill the crack with comcrete mix up to the top. The top 1/8 corner area that is low can be filled with thinset, After it sets, apply an anti fracture membrane like Redgard, Hydroban, Protecto Wrap, etc. I would apply the membrane to the whole corner section and out past the crack 6 to 8 inches. Like CX said, it will probably still crack.

[BillBo]

Thx, Davy!

Originally Posted by Davy

I would apply the membrane to the whole corner section

Since it's tiles on concrete, I was planing on using a membrane for the entire room anyway. The crack looks ancient, so I don't expect too much movement and maybe nothing bad will happen.

[ob1kanobee]

You don't have to put underlayment all over the entire room BUT it won't hurt. Sometimes it can be overkill but by all means if it will make you sleep better at night.

Now me, I would NOT fill that crack nor most any crack running across the floor like that. Reason being is the last thing you want is vertical movement as opposed to side to side movement. If the crack is filled and it needs to move, I feel at that point it will want to move up and down as opposed to side to side because it can't move side to side cuz you done filled it (get what I'm saying?)

Now this is just my opinion but I sorta trust my opinion on these sorts of things.

I've tiled over much worse with membranes and seen the jobs throughout the years and years later. You should be fine and I wouldn't worry about it.

Come back or stick around but 20 years from now let us know how it's working out for you LOL. I'm sure the only problem you'll have at that point is some dirty grout.

[Davy]

I guess we all have our own way to look at it. He said the crack is 2 inches wide so I felt it needed to be filled with something. I may be wrong but to me the slab will do what it wants to do regardless of the fill. If it wants to open up, the fill won't stop it. The fill might keep the crack from closing up, which I would think would be a good thing.

I did a bath floor about 10 years ago that had a big crack, 1/4 to 3/8 wide and it did have vertical movement. The crack was over near the wall, maybe 10 to 12 inches away. I covered the area with Protecto Wrap with the primer.I told the homeowner that this would fail for sure but he had his mind made up to use tile on the floor. He knew I couldn't stand behind it and we kept extra tiles. He called me back about something 2 to 3 years later and I asked him if the tiles ever cracked and he said no. No two slabs are the same so we never know if and when it will decide to move again.