do most concrete slab homes need isolation membranes? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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05-29-2019, 01:58 PM
When you install tile on a typical 1500 sqft slab home, do you normally see cracks everywhere?

I'm gonna be pulling out the carpet next month, and I dread to see how many cracks there will be.

I tiled the dining room a few years back, and there was a hairline crack which I tiled over, and those tiles eventually got hairline cracks as well.

Do you guys just roll on the pink stuff? Mapelastic CI or Redgard ?

If i'm putting in 8x24" tiles, I just roll the CI 24" left and right of the crack, right?

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05-29-2019, 03:27 PM
You need to cover at least three tiles in either direction, Having said that, if the cracks are can do this. If they are vertical...bad luck and I see carpet in your future......:gerg:

05-29-2019, 05:43 PM
In many cases, I just cover the slab with Laticrete Stratamat. It not only protects the tile from cracks that have already formed, but from cracks that form in the future, as long as they don't expand more than 1/8".

Cheap insurance when the alternative is possibly tearing it all out down the road.

05-29-2019, 07:25 PM
I figure enough in the job to cover the whole slab with Redgard or Auqa Defense. I've had good luck using these products but they have to be installed the right thickness. Like Kevin said, it's cheap insurance.

05-30-2019, 07:30 AM
I used Ditra on the entire slab. Why use something just localized on a crack? The whole slab is a potential crack.

05-30-2019, 09:32 AM
Ditra is better than nothing, but it isn't a crack isolation membrane.

I use Ditra if I need the floor to be waterproof, and Stratamat for crack isolation.

05-30-2019, 09:45 AM

Ditra does the same thing. Call it whatever you want.

Metropolitan Ceramics
05-30-2019, 10:43 AM
Concrete always cracks as it cures. Sometimes those cracks go where you want them - for example in a sidewalk where control joints are cut in every 4 feet so the cracks form there. Sometimes those cracks go wherever they want. Usually if your slab has been in place for several years, the cracks due to shrinkage of the concrete have already developed and you can safely 'spot treat' them by covering the crack and going out 3 tile sizes to either side. As others have pointed out though, this won't help if new cracks develop due to settling of the house, for instance. If settling is an issue in your area, full coverage of your crack isolation membrane is recommended.

Roll-on products like Mapelastic CI are perfectly fine at stopping cracks from propagating up through the tile or grout and are very easy to apply. Membranes like the Stratamat or Ditra also protect the tile from cracks below but do it by deformation between the layers of the mat instead of by stretching of the membrane. In your situation, the distinction isn't really all that important. Either will work, you can purchase based on availability and your comfort level with installing. If it was me and my house, I would roll on a crack isolation product like the CI instead of messing with mortar, membrane, rolling, and filling holes with more mortar.

05-31-2019, 04:30 AM
this home was built in 1966.

Since slabs always require rebar, I would hope there is no vertical plane cracking.

05-31-2019, 08:18 AM
Since slabs always require rebar...Not so, Paul. There are other methods of reinforcing SOG concrete. Post-tension cabling is a popular one.

...I would hope there is no vertical plane cracking. Even concrete slabs with steel reinforcing can, and frequently do, end up with vertical displacement between sides of a crack.

My opinion; worth price charged.

05-31-2019, 02:09 PM
In many locations rebar/cables aren't needed. CA is an interesting place tip to tip, if you don't have expansive soils and a few other details align, slabs don't require bar at all. Cheap builders like to VE it out and engineers will support that in many instances, especially for SFRs.