Level with Thinset/Mortar???


Old 07-14-07, 12:04 AM
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Level with Thinset/Mortar???

Standard preamble about searching for, but not seeing quite what I am looking in other threads.

Project: To level the floor in a wood-stove alcove added to the home, at some time after 1976, so I can install new tile/slate. Previous stove stood on a pedestal 8 above floor-level of the rest of the room. Now the entire room, alcove and all, sits at (almost) the same level

Area to be tiled: ~89" wide x 58 deep total. Wood-stove alcove proper measures 89 wide by 37" from back wall to where it meets flooring of the living room.

Construction: Alcove sub-flooring is (I believe) 1x6 t&g; rest of room is OSB. Joists below are inaccessible, but it appears to be 16 oc.

Problem: Alcove sub-flooring is 1/8" lower than that of the living room at the joint and slopes to a total of 3/8" at the back of the alcove, a distance of 37".

Setup: Tile shop suggested using mortar/thinset to level the floor as opposed to a "true" leveling-compound.

- Is this normally done?
- If I go this route, do I:
o lay the mortar and immediately place the backer-board on top, let cure, then install tile?
o Or let the mortar cure for a few days, then set the backer and tile?
- 1/4" or 1/2" backer? For ease of aligning the tile I like that with the grid embossed (Hardy Plank?), but only find this in 1/4" thickness. Long-term, I prefer a quality, finished product and believe the is the way to go for structural integrity.
- Is there a better way to do this?
- Am I splitting hairs? I think not if setting a, very heavy, wood stove on the finished product.

I look forward to any and all advice.


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Old 07-14-07, 04:59 AM
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First issue is the planking...You need to add atleast 1/2" ply over top before adding any sort of membrane or cbu. Either replace the planking with the same thickness plywood or osb--or--cover the planked area with 1/2" ply and then the osb with 3/8 ply which would bring the two areas in plane. Too bad you can't access things from below as I'd be real concerned about bridging the intersection of the osb/planked area without being certain as to if it needs to be treated as a cold joint or not.

Hey, isn't this the second thread with a tile shop giving questionable advice in about a week? Maybe they're all recruiting staffing from the big box stores now?
Old 07-14-07, 05:18 AM
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How about removing the planking, replace it with 3/4 inch ply wood, and do a mud set? That eliminates the need for leveling compound or CBU and can be made level with whatever other flooring you may have or be putting in. Just a thought here.
Old 07-19-07, 11:26 AM
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Firstly, thank you for your responses. Secondly, I apologize I've been unable to thank you as I had to be away unexpectedly for a few days. Thirdly, I need to make a correction to my initial post.

In my initial post I listed the sub-floor in the alcove as "1X6 t&g", which was wrong and I should know better than to type when tired. It should have read 2x6 t&g sub floor.

Since I've found that I have indirect access to the sub floor under the alcove I can confirm that I have joists at 16"oc and it insulated from the back of the alcove all the way across the joint and throughout the living room.

My questions:
- What is a "mud set"?
- What is a "cbu"
- How do I treat as a "cold joint"?
- Would a photo or 2 be helpful?

Thanks once again.

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