Cracks on my cement floor....

bcbud3

I have a 2" concrete slab with radiant floor heating. The floor is about 24 years old and has some cracks in it. The floor also has some low spots in it. I talked to three different tile guys and 2 said that self leveling would be best solution. The 3rd tiler said that self leveling was not good on radiant floor and that there could be issues in the future because of the clc. He recommended schluter product. That is too expensive for me. He then recommended lathe and plaster mesh laid on the floor and then a coat of quickset put over top. Kind of a new sub floor on which to lay the new tiles. What would be the best solution here?

ccarlisle

Need more info: do you have radiant heat inside the clc? or on top? What type and size tile are you considering? is this a basement? is moisture an issue?

What % area would require the self-leveling cement? a fraction of the whole or more than half? are the cracks stable or not?

Once we know that, we'll give better answers but if you plan on tiling directly over concrete or clc, the cost of the Ditra will have be viewed with what your tolerance is for cracks in the future. Some can't live with cracks in their tile - so Ditra at $2 per sqft is a form of insurance. Others don't realize the other benefits of Ditra if moisture is an issue...

bcbud3

The radiant heating is in the concrete slab. The slab is 24 years old so i pretty sure it's settled now. The concrete on either side of the cracks is level. Not sure qhat % would need clc. I don't think there's much moisture in it either. I'm not sure how many dips there are. I am wanting to put 3/8 porcelain (approx 350 sq ft) on this floor for my kitchen. This slab is on the top floor of my house (above grade)

rusty baker

A slab upstairs? Is this concrete or gypcrete? It makes a world of difference on what you use.

__________________
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bcbud3

it's concrete. The floor was a 3rd floor addition and instead of adding forced flow heating they ran infloor heating (pipe buried in concrete.) The slab is only max 2" thick

ccarlisle

OK...just to make sure we understand each other, you have a 2" thick 'clc' slab (i.e polystyrene bead-containing 'concrete') that has a polyethylene pipe running through it for heating, and you have in-plance cracks (i.e. no change in height) is that it?

If so, those cracks are probably stable and flush with the surface unlike on grade where settling might have come into play. I also gather there are a few low spots here and there - but nothing like a 1" difference, right?

If that is what you have, I would opt for putting self-levelling cement patches here and there, not enough to affect the heat transmission of the pipes, max 1/2" at the center and feathered out to the edges. Moisture is not an issue here so the use of Ditra is less, but still a worthwhile consideration for the future. But again it comes back to your tolerance level of cracks.

If cracks do appear, the tiles are easily replaced...so make sure you have enough extra tiles for the next 20 years or so, say about 10%.

A 50lb bag of SLC will give you coverage of about 18 sqft at an average thickness of 3/8". The thinset you use to place the tiles will fill in the rest and any small voids here and there under each tile.

Bud Cline

The first thing you do is stay away from that guy - he has no idea what he is talking about. SLC is one of the primary state of the art recommendations for this type of work.

Being on a third floor the cracks mean little. They are probably very stable and are a result of structural shifting over the years. They probably radiant from something having to do with the hardware and piping used to install the heat system. They are not subject to subsurface fluctuations in soil moisture-content and other stuff like that. If SLC won't work then nothing else will either, especially tile.

I can tell you that Schluter does not "cost"...it "pays". But I won't try to sell you Schluter even tho it could be the right thing to do here.

NO WAY !!!
Not if he is suggesting a gypsum product. Gypsum and tile DO NOT go together under any circumstances.

This brings us back full-circle to what was used originally. Typically in a wood structure and on subsequent floors above grade a lightweight product like Gypcrete is used to keep the weight down.

Also typically when that type of heat is used above grade in a wood structure a product like Gypcrete is used to embed the heat system.

There's two votes for Gypcrete (or a like product) existing there

NOW, the problem if it is Gypcrete is that the floor requires special attention if it is to be compatible with a tile installation. The tile MUST BE isolated from the lightweight product.

Now we are back to Schluter DITRA again.

To repeat...it doesn't cost, it pays.

Besides, How big can this room be anyway? 150 square feet maybe?

bcbud3

The room is about 350 sq ft. The previous tile was mudded directly onto this floor and there was no cracks on any of these tiles (they were on the floor for over 20 years). I had to chip up the mud once i popped up the tiles. I'm thinking some slc on any low spots will be the answer. How do you tell the difference between concrete and gypcrete?

Bud Cline

Well there ya go......!
Sounds as if you may be in good shape. Now I'm not convinced SLC is really necessary - maybe just a good Portland-based cement patch material.

Gypcrete (in my experience) appears lighter and more grainy than cement. It is usually fractured everywhere and very dusty. It also scratches easily.