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Unread 12-23-2008, 04:20 PM   #1
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Odd repair job

I'd like some opinions on how to best handle this repair.

I removed the last row of 12" tiles, which were cracked. Picture shows why they cracked. The tiles to the left are on a mud bed and are fine. The last row of tiles had only a couple of inches on the mud bed and the rest directly on 1/2" ply. Thinset of course didn't stick to the ply and came up clean.

To complicate matters a bit, the mud bed part is on a dropped subfloor. Meaning ply is supported between joists and sunk flush with top of joists. You can see the joist near the center of the photo. The 1/2" subfloor to the right is not dropped. It sits on top of the joists.

I'm thinking of cutting out the 1/2" ply on the right and extending the dropped subfloor, with proper reinforcing below. But not sure if I want to (or can) extend the mudbed. The existing mudbed is only 3/4" barely, maybe 5/8", and you can see how bonding to the existing bed is not real promising.

Would it make more sense to put some 1/4" hardy in there and do a medium bed install, like Custom's Marble & Granite, or several layers of flexible thinset like Custom's MegaFlex? Or do you think extending the mudbed is OK because of the lath? What would you do?
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Unread 12-23-2008, 04:40 PM   #2
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The pic a a little tought to see. Maybe if it was rotated 90 degrees, it would make more sense that it's a floor.

If you can drop the subfloor and make it so a properly supported layer of cement board could be installed right next to the mud bed, nice and flush with it....you could tile on that and leave a soft joint of caulk in the grout space where it met the other tiles.

But bonding to that mudbed isn't gonna happen without putting in a mud bed with your new metal lath overlapping onto the old metal lath. And that would require the removal of a row of tiles and at least the first couple inches of the old mud bed to expose the old lath.
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Unread 12-23-2008, 07:26 PM   #3
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like bubba (kurt??) says you need to take those tiles up and remud it and span the tile over the joint, you'll have a cold joint where your 2 setting beds meet and i can promise you that that joint will crack within 6 months of the repair.

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Unread 12-23-2008, 07:35 PM   #4
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The best you can do is try to overlap the lath by 2 inches, and spread some thin set on the edge of the old mud bed before extending it with the new. You may have to take up the second row of tiles to do it.

No guarantees, of course.
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Unread 12-23-2008, 10:46 PM   #5
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Overlapping the lath is no problem. Maybe not 2" overlap everywhere, but at least 1" everywhere, 2" most places. See picture.

My question was basically this: Extending the mud bed, no matter how and how well, I have a cold joint. Would a medium bed mortar or several layers of flex thinset make for a better bond to the existing mudbed, and therefore less likely to crack in the future?
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Unread 12-24-2008, 03:11 AM   #6
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I think the best chance for success for this is to drop the subfloor in the area to the right and recess the ply between the joists. I would cut away the mud and lath on the left side of the ply so it is flush with the existing 12x12 tile on the left. Then, float in new mud over lath on the right side to the same thickness as the floor on the left. Set and grout the replacement pieces of 12x12 tile and leave a clear joint all the way through to the subfloor both on the left and right sides of the new tile. Then, I would fill the joints between the two fields of tile with color-matched silicone.
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Unread 12-24-2008, 07:24 AM   #7
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