how do you prep this subsrate - Contractor Talk - Professional Construction and Remodeling Forum

floorinstall · 10-22-2007, 05:50 PM

I am bidding on a job that I have not dealt with before. I need to remove 800 sq.ft. of tile and replace it. The substrate is 3/4" plywood, I don't know the joist size but it is 16" o/c with a span of 15 feet. The floor is 15 years old and dose not seem to have much deflection. On top of the plywood is 2 inches of light weight concrete. I will be taking out the tile and reinstalling 13 inch porcelain tile, the original tile seems to be stuck well except for a few isolated areas. Out of 800 sq.ft. only 15 to 20 square feet has loosed or cracked. I was thinking of removing the tile and installing an isolation membrane for noise reduction and crack suppression. I have not taken out the tile but there are no long cracks in the tile that would indicate cracks in the substrate. My concern is rigidity of the sub floor and would the isolation membrane buy me cheap insurance against future problems with cracks telescoping and tile coming loose.

Floordude · 10-22-2007, 10:10 PM

Sounds like you have a mud bed & lathe under the existing tile. Done like it was done, when guys knew what they were doing.

Your going to need to make up the 2" in height your fixing to bust out.

I would go over the subfloor with anthor layer of ¾, and use CBU or Ditra.

MattCoops · 10-22-2007, 10:25 PM

option mentioned above is great idea.
No one really floats floors anymore, there's so much newer technology.

I think the Ditra acts as an isolation membrane also.
And if you use the kerdi band on joints I believe you make it watertight.

I don't use Ditra much.
Most of our installations we're using DensShield water-resistant backerboard.

floorinstall · 10-22-2007, 10:32 PM

It may be a mud float in the area of the utility closet it looks like a float finish. I know it is not a drypack. Do you think it is possible ti chip out the tile without taking out the entire mud bed. The unit next door was done about a year ago and I don't believe that they removed the entire bed.

MattCoops · 10-22-2007, 11:19 PM

you can chip off just the tile and then use a thin coat of SLC

reveivl · 10-22-2007, 11:55 PM

You really do want to find out the dimension of the joists. If the 2" bed is not damaged (cracked) you're probably good to go, but why not be sure? Once you're sure it's stiff enough, throw down a membrane and set some tile.

HJ1 · 10-23-2007, 09:01 AM

Sounds more like gypcrete than a mud bed to me. If thats the case it'll be hard not to do damage to the gypcrete when removing the tile. Is this a condo or coop apartment? This stuff is often used in condos for its sound reduction qualities but is not great for tile as its really unstable and susceptable to cracking and crumbling. Many condo associations will not allow you to remove it.

You may be able to patch it up and go over it with an isolation membrane.

floorinstall · 10-23-2007, 08:16 PM

I think it is gyecrete. They are calling it light weight concrete. I like the idea if chipping out the tile and floating the floor to repair the damage and install an isolation membrane, Do you know if the common practice is to us a metal lath with this product or is the concrete going to disintegrate when I try to chip out the tile?

HJ1 · 10-26-2007, 02:28 PM

In my experience, this stuff breaks and crumples real easy. You need to be careful and gentle when removing the old tile. The tile should however come up pretty easy. You said some of the tile was already coming up right.