Tile over uneven slab (old garage floor)

[joea]

First, due in part to prior assistance received on this site, my bathroom shower re-do turned out well. Thanks.

Have moved on to working on a converted 2-car garage, that was converted into a "split level" room. An area about 20x20 is framed out as a "raised" area (but even with the rest of the first floor), with steps down to an 8x20 are that leads to the "front door", which is at ground level.

The original conversion (prior owner) had built this lower level as ceramic/???set/plywood/dimensional lumber, on slab. I ripped all this out as the tile was cracked and the sub floor seemed to flex some.

The slab is not level, it tapers down toward the door area some 3 inches or so. A typical garage floor, so I am told. The old framing tapered from 3 inches near the door, to about 1/2 inch where it ended at the raised area.

I am faced with a decision on how to level this, yet provide a solid base for new tile. I think there are only two sensible choices

1 - pour a bed of "sand mix" (due to it being only 1/2 inch thick at one end)

2 - re-frame a sub floor, this time, much less flexible.

My additional concerns - There is a "musty" odor that seems to emanate from the existing slab. The concrete appears dry. That odor is now noticeable thoughout the room. I want to make sure that does not seep thru when all is finished. Thus, I think I must put down some kind of vapor/insulation barrier. Such as the "bubble/foil" stuff that is around. This, with taped seams, would provide a moisture/odor barrier and a "thermal break" between the room and the slab. I would extend this barrier to cover the entire room (crawl space under raised area, for additional benefit.

Problems I see -

1 - In a "slab over", there would be no bond between slabs. That, I guess, would be "a bad thing"

2 - in a frame over, I would have nasty time cutting and shimming the framing, to be level. And, by the time I put 5/8 or 3/4 plywood and backer board over the framing, I would be too high to clear the door.

Suggestions?

joea

[Davy]

Hi Joe, the tiled area can be mudded up with 5 to 1 dry pack bonded to the old slab with a slurry of thinset. Ditra could then be put down over the mud to seal it off. Not sure how to seal off the other area that is under the framed raised area.

[joea]

Well, now ya gots me. I guess I'll spend the rest of the afternoon searching on "dry pack" and "Ditra".

"Dry pack" I can sorta intuit, but "Ditra" draws a complete blank. By 5:1, that means 5 sand, 1 Portland? Dry means that the mix does not slump and must be packed into place?

I forgot to mention that the existing slab appears to be painted over much of its surface. It is not expoy, I'm pretty sure (from the looks of it and from when it was done). Will I have to abrade that off for a good bond?

As far as the crawl space, I guess the best idea is either poly or the bubble/foil held down with dabs of adhesive and the seams done with metalic foil.?

And thanks for the speedy reponse.

[John Bridge]

Hi Joe,

The Sand mix or "dry pack" mortar is explained in our Liberry.

Ditra is a flooring membrane made by my patron company, Schluter Systems. It is glued down with thin set, and the tiles are set directly to it with more thin set. Have a look at the Schluter site, and I'll put a picture below as well. http://www.schluter.com

[joea]

Thanks John,

So, where to buy this Ditra stuff? Checked about a bit and found no one. And, how does one join/seal the seams, as it appears to be 3.3 feet wide?

joea

[Davy]

Around here Daltile can order it, takes a week or so, Interceramic keeps it in stock.

Kerdi band can be used to seal the joints completly.

[cx]

I agree with Davy on the mud bed over the existing concrete, Joea. And yes, that sounds like a pretty typical garage floor. I usually try to get 2.5 to 3 inches drop to the door on a 24 foot garage. Gives you something in the neighborhood of plumber's fall.

Some of your smell problem may be from dampness in that slab. Unfortunately, builders will frequently not bother with a moisture barrier over the fill in the garage area of a foundation slab, the rationale being that it is not conditioned space. Prolly saves 25 bucks total, including installation, on the cost of the whole house. Never have understood it.

Anyway, cut you a two foot square piece of clear polyethylene, any ol' thickness you have laying about, and duct tape it over the middle of the floor, sealing all four edges well. Leave it there for a day or two and see how much water condenses on the underside of the plastic. Give you an idea if you have a real consideration there.

I'm afraid I don't have a clear picture of your crawl space situation, so I can't comment on that. Maybe more description would help.

Or maybe not.

[joea]

Yep, I would consider that normal over 24 feet, but this 3 inch drop is in the last 8 feet. Not the only oddness I've seen in this building.

If I do have a moisture issue (and I probably do) will the "Ditra" stuff not seal the moisture well enough? I'll probably need to find a dealer closer than Texas.

Anyway, the crawl space - The original garage floor (slab) was about a 20 inch drop from the main house floor. They framed out a new floor, level with the main floor, in a rectangle shape. They laid up double 2x12's down the center, lengthwise (blocked at one end to be level) and "hung" 2x10's, 16 on center, between that and each side of the room. So, there are 2x10's from this center post, to the house/garage wall and the same on the other side, to the garage/exterior wall. This leaves me with the center 2x12's pretty much flush on the slab, at one end, and about 2-3 inches above the slab, at the other. And, about a 12" crawl, under most of this floor framing. A tight fit, for sure.

This left an rectangular 8x20 or so as a "lower level", where they laid tile over
plywood over angle cut 2x4's and shims, laid/nailed to the slab. This is what I removed, to the bare slab and where I need to put a new floor.

I was going to deal with the "knee wall" that results by a means yet to be determined, but that will allow future ease of access and a means of ventilation.

I could, maybe, forego any moisture barrier in the crawl, and add mechanical ventilation in the crawl. A year ago, I bought one of these Energy Recovery ventilators, to change change interior with exterior air, yet recover heat and humidity. I have yet to hook it up. I could set it up to draw air from the crawl, as part of the whole house return. Wadda ya think?

joea

[flatfloor]

You can purchase Ditra right here through our store click on it and it will lead you to Schluter products. The distributor is Dave Taylor one of our members. He is a growing boy and needs the bee..er, food money.

[John Bridge]

Dave's prices are good, and they have a store in Jersey. Only takes a day or two to get it to you.

http://www.tileyourworld.com/catalog...ffdc3268272764