Floor tile mortar bed crumbling. Tear up and replace?

The bath floor in my 1984 house is crumbling in high traffic areas. . When I pull up the loose 2" tiles, the mortar bed is in 1" and smaller chunks. It doesn't help that they laid the tile with the paper backing still attached, not the best thing for sticking to cement.
I've been doing temporary patch repairs by cleaning off the backs of the tiles, vacuuming up the dust, and re-laying them in wallboard compound.
I guess I'm going to have to tear the whole mess out, put down a sheet underlayment, and set the new tiles in mastic.. The hard part will be getting the height set so they mate with the wall edge trim and the toilet flange.
I don't understand what advantage bedding the tiles in mortar is supposed to have, when the floor underneath is going to flex. I suppose it might work on a slab, but not on wood. -- Email reply: please remove one letter from each side of "@" Spammers are Scammers. Exterminate them.
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Tile only works when the floor underneath does not flex.
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Doug Warner wrote:

for real. i'd put up with long as I could anyway, at some point, you might have replaced all the weak spots, it could stay another 6 years.
im doing a bath right now, and Im putting a flex additive in the mix
I know what you mean about getting the heights the same.
you say mastic, i've never tried this, but I hear that vynal glue is excellent for tile repair. something like this would help the tiles stay low.
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On Sat, 17 Dec 2005 20:41:42 -0500, Doug Warner
Sorry you're having problems, but...

Loads of people have tile floors on other than slabs.
I have two bathrooms with 1" tiles. I don't know what is at the bottom of the whole thing, but it comes out even with the carpeting on plywood in the rest of the second floor.
I guess they must have used that stronger board that they push now -- I forget the name -- but I may never know.
Remove NOPSAM to email me. Please let me know if you have posted also.
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If they laid the tile with paper, they probably didn't know how to get a non-flexing floor to lay it on. If it's just plywood over joists (16" OC) in a stick frame, the subfloor should be at least 1 1/8" thick plus a 1/4" layer of cement board (Hardibacker is my favorite). If you want to use mastic and stick with the small tiles (up to 2") then the floor movement is of less concern. Also, as far as a new floor lining up with other things, the doorway is your biggest concern. A big difference there will have to be transitioned with a threshold. Takes some skills to cut and fit that. Being level with the flange is not as important. If you end up a bit high, use double wax rings to ensure a seal. Around the trim, lay the tile to within 1/8" and fill that gap with caulk that matches your grout. TEC brand is good for this, get it at a tile dealer. It's more expensive than the crap box stores sell, but for the amount you'll use in a bathroom it'll be worth it. Good luck!
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Spammers are Scammers. Exterminate them.
Seems your wasting your time setting tiles in joint compound.
It is not hard to get the new floor to finish out at the existing height. After rip out just measure the subfloor to the UNDERSIDE of the toilet flange. Deduct the thickness of the new tile and the thickness of the new cement board. This will give you the thickness of the plywood underlay you will need to install. So if you measure 1" your new tile is 1/4" and you use 1/4" durarock you need to install 1/2" plywood underlay.
If your "wall edge trim" is sanitary base you will not be able to save it and should figure on replacing it also.
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