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Old 12-22-2008, 05:54 PM   #1
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Help! Tile-over-concrete slab problems


Howdy everybody, I've got a mind-bender for you that I hope someone can help with.

I'm replacing the 30-year-old vinyl flooring in our laundry room with 8" poreclain tile. The house is a tri-level, and the laundry room is in the two-story part of the house, in the basement, with one wall abutting the one-story part of the house, and another wall being external. This comes into play in a moment.

We've pulled the old vinyl out and gotten most of the adhesive backing off (and THAT was a good time, let me tell you), so now we can see what's underneath ... and it ain't pretty, for two reasons.

Expansion joint: first, there is an expansion/isolation joint between the concrete slab that makes up 90% of the room, and the last ~5" of the room floor running along the wall, which apperas to be part of the slab or foundation of the one-story part of the tri-level. The joint is about 1" wide and is filled with styrofoam. It appears that it was plastered over under the vinyl to make it somewhat smooth, but some of the plaster has crumbled. The 5" strip is about 1/4" to 1/2" lower than the main slab floor.

Raised foundation sill: on the external wall, we have a different problem. about 5" from the wall, the smooth level-ish slab suddenly becomes "lumpy" concrete, that sticks up above the slab maybe 1/8 to 1/4". I'm no foundation expert, but it looks like some form of "sill" jutting out from the external foundation ... but I'm not sure.

Full set of pics at http://flickr.com/photos/jeffchrisop...7611465010391/.

So ... both of these things are complications in our tile-laying plans. I could fill the expansion joint with levelling compound or thinset or something, and use similar to bring the level of the 5" strip on the other side of the expansion joint up to level ... but that seems like I'll get broken tiles or at least cracked grout at some point. The raised foundation sill is uglier - do I chip the dang thing down, then use leveling compound to smooth it out? Can you send concrete down?

Other info: the expansion joint wall will, in general, not have much load on them, and won't be easily viewable, as it will run behind the toilet, sink, and laundry machines. The spacing between the laundry machines and the wall SHOULD mean they won't load any tiles that bridge the expansion gap. The external "sill" wall is another story - the laundry machine stack feet will be on those border tiles ...

Anyway, there's my dilemma ... thoughts? Any ANY help appreciated.
- Jeff

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Old 12-22-2008, 07:59 PM   #2
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Help! Tile-over-concrete slab problems


Hey Jeff,

I took a look at your pictures, and you don't have a perfect situation for tile, but one that is fixable.
Step 1: I would try to chip off or grind down the roughest spots along the outside wall. Sweep and vacuum until it is perfectly dust free. I would also try to fill the 1" gap with something sturdier (maybe even wood).
Step 2: Sounds like you are familiar with leveling compounds. Use a quality, portland latex mix such as Ardex or something comparable. Not a white Dependable powder or any lesser grade.
Step 3: I recommend using an uncoupling mat, such as Schluter Ditra Mat. This is an orange "waffle-like" roll that goes down between the concrete and your tile.
www.schluter.com
The waffle design of this product will absorb any movement from below and keep it from transferring to your tile and grout. This is one of the best tile underlayment products that we use. It is very versatile. It is also a waterproofing material.
Once you have the floor smooth, you install the Ditra Mat with the same mortar that you will use to set your tile. You can do a small amount of additional leveling with the mortar coat that the Ditra Mat lays in and again with the mortar bed that the tile sets in.
Obviously, with your inconsistent subfloor, you need to use some type of "uncoupling" material or you will have cracked tiles and grout down the road. Ditra Mat is widely used and highly recommended by many installers.
Ditra is available at most quality tile shops nationwide.
hope this helps,
good luck
Kurt

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Old 12-22-2008, 09:08 PM   #3
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Help! Tile-over-concrete slab problems


Just adding to the advice already given...

You should not tile directly over an expansion joint. There are very clear procedures for this. You should either a) use a soft joint aligned with the expansion joint, or b) install an expansion profile product like Schluter's Dilex.

Just to be clear, yes Ditra itself is waterproof but for an actual waterproof floor installation, the addition of Schluter's Kerdi is needed.

If you use a leveling compound, check the instructions carefully before you begin. Some require the use of a primer over the cement slab before installing.

Good luck!
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Old 12-23-2008, 11:06 AM   #4
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Help! Tile-over-concrete slab problems


Quote:
Originally Posted by TileAndTimber View Post
...Step 1: I would try to chip off or grind down the roughest spots along the outside wall. Sweep and vacuum until it is perfectly dust free. I would also try to fill the 1" gap with something sturdier (maybe even wood).
I've got an angle grinder that I plan to go to town with this morning. That's straightforward, at least.

Quote:
Step 2: Sounds like you are familiar with leveling compounds. Use a quality, portland latex mix such as Ardex or something comparable. Not a white Dependable powder or any lesser grade.
I've got a big ol' box of Henry 547 UniPro (http://www.wwhenry.com/prod-547.htm). Portland, but no latex mentioned ... good enough?

Quote:
Step 3: I recommend using an uncoupling mat, such as Schluter Ditra Mat. This is an orange "waffle-like" roll that goes down between the concrete and your tile.
www.schluter.com
The waffle design of this product will absorb any movement from below and keep it from transferring to your tile and grout. This is one of the best tile underlayment products that we use. It is very versatile. It is also a waterproofing material.
Once you have the floor smooth, you install the Ditra Mat with the same mortar that you will use to set your tile. You can do a small amount of additional leveling with the mortar coat that the Ditra Mat lays in and again with the mortar bed that the tile sets in.
Looking at the Schluter material, I don't quite get where I'd use Ditra. I'd still have to honor that joint separately, yes (as angus pointed out)? I looked at some of the Schluter Dilex products (at http://www.schluter.com/141.aspx) but I can't seem to figure out which one would be appropriate - seems like they are either too shallow, or too narrow, or can't be retrofitted into an existing joint ... am I missing one?

There don't appear to be any solutions that would allow us to cover up the fact that there is an expansion joint there, yes? Sounds like we'll have to have a ~5" tile on the 'small' side, then the expansion joint thang, then the rest of the room field on the main slab ...?
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Old 12-24-2008, 02:06 PM   #5
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Help! Tile-over-concrete slab problems


Anyone?
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Old 12-24-2008, 02:33 PM   #6
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Help! Tile-over-concrete slab problems


You have a tough situation for sure.

I have used Ditra in the past and have had great results. It is great stuff and it can be used over concrete. However I don't know if you use it over an expansion joint. You should call the Schluter Ditra folks and ask them directly. Has the joint moved? Did you have any reflective cracks in the tile. If so, that may indicate that there is movement. Discuss this with the Ditra folks.

Are you dead set on tile? I used a "pergo" type inter-locking floor in my basement and it has held up great. I too had very old glued down kent tile floor, only I could not get the glue up as well as you seem to have. I was concerned that nothing would adhere to the floor (I wanted to tile it also) so went for the interlocking floor. My basement is dry, so I don't have any issues, but I do believe that they make a interlacking floor that is moisture resistant.

I hope this helps

Bob
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Old 12-24-2008, 05:22 PM   #7
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Help! Tile-over-concrete slab problems


You have a foundation footing with the slab poured inside the footing wall. No big deal. The problem is there was probably a time when the elevation of the two elements where identical, now they are not. This tells you the slab has sunk slightly.

You can resurface the slab with Self Levelling Compound raising it to the same elevation of the footing wall. You must still honor the expansion joint. This can be done with a piece of wood used as a temporary dam or even sill foam for that matter.

Once the elevations are matched tile can be installed but the expansion joint still must be honored. Still not a big deal. You can lay the tile overlapping the joint and create a grout joint of about 1/4" overlapping the tile on both sides of the expansion joint. When grouting don't grout that joint. Instead use a matching sanded caulk to fill the expansion joint.

You will not know the (soft joint) is there and all will look great. The soft joint will easily absorb some movement but if things move up or down the joint will likely tear open. The biggest problem is going to be if you have to cut tiles mid-field to honor the joints but this is done routinely.

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