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-   -   tile over concrete (https://www.johnbridge.com/vbulletin/showthread.php?t=129947)

Brown 10-16-2020 11:44 PM

tile over concrete
I have 43 year old home with a slab on grade kitchen, laundry room and 1/2 bath and would like to install porcelain tile in the laundry room and bath.
I'm undecided on what to do for the kitchen floor right now.

The floor had vinyl covering and I had an asbestos remediation co. remove it. Now I have 400 sq.ft. of bare concrete.

The kitchen floor is in generally good shape with a couple of hairline cracks and numerous divots from removing tack strips. (half of the kitchen was carpeted!).

I don't know if self leveling should be used in the kitchen to fill the divots or just use concrete patch. There are no cracks in the bath and laundry room.

What is the procedure for installing tile? Do I need to install an uncoupling membrane or can I simply put thin set on the concrete and set the tile?

Which raises the question do I apply something to the concrete to make the thin-set stick to it?

I am looking at using large format tiles (12 x 24) that are American made and are flat.

Tool Guy - Kg 10-17-2020 06:39 AM

Welcome to the forum, Jack. :wave:

First thing to ask about is moisture. Do you have any moisture issues going on?

Second thing to understand is if your slab is porous or not. You want open pores for the mortar to stick. Pour a few ounces of water on the slab and wait 5-10 minutes...then wipe off all the excess. Hopefully, some moisture has sunk in and has temporarily darkened the slab. If so, you’ve got open pores and a surface that’s really to be stuck to. If the slab remains visibly unchanged, you may need to run a diamond cup grinder wheel (rentable) over the surface to rectify the sealed pores.

As far as the divots, they aren’t a big deal. Whatever setting material you’re going to use can very likely be used to fill them ahead of time. Just mix up some mortar and patch them with a little putty knife.

Assuming you don’t have moisture issues, you want to use a crack isolation membrane (rather than an uncoupling membrane that doesn’t have a rating for crack isolation properties). For an easy crack isolation membrane, you may want to consider using Custom Building Product’s RedGard or Laticrete’s Hydroban. These are both paint-on liquid membranes. While they don’t go on as easy as paint, they aren’t hard to apply with a roller and afford decent crack isolation properties. If you need a high-performance crack isolation membrane, Noble makes a sheet membrane called NobleSeal CIS that is the best of the best.

If you do have slab moisture issues, let us know.


ss3964spd 10-17-2020 07:07 AM

To add to Tonto's post, given the 12X24 large format tile you intend to use, as part of your slab prep you'll also want to use a long straight edge to check for floor flatness. I believe the requirement is that the floor can deviate from the intended plan by no more than 1/16" in 2 feet and by no more than 1/8" in 10 feet.

In other words, if the slab has high spots you'll need to remove them. If it has low spots you'll need to fill them.

Davy 10-17-2020 09:58 AM

What the others said. I'll add that Lowes has Mapei's Aqua Defense, it's a paint on membrane similar to Redgard. You just want to get the membrane thick enough, usually credit card thickness is about right. I usually apply it in two coats to get that thickness.

For thinset, any of the LFT (large format tile) thinsets will work.

Brown 10-18-2020 01:53 PM

Thanks for the warm welcome and the advice!

The slab is bone dry-no moisture issues.

I did the water test and it soaked it all up so I guess it is porous enough.

The laundry room is 8ft x 6ft and it has a slight slope to a drain in the middle of the room. The drain cover is 5"dia. and has a slope that starts about 2" out from the edge of the drain cover and down to the drain which is 3/4" from the floor.

I didn't realize the slop in the rest of the floor before until ss396 mentioned the requirements for large format tiles and I went to check it and found the slight slope.

So that means I'll have treat the tile as a shower floor sort of for tile size. No more large format tile!

The RedGuard or the Hydroban is something that I will use for the isolation membrane.

I appreciate the advice that I receive here because I consider the John Bridge Forum as the Gold Standard for advice that can be trusted.

Thanks again, guys.

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