Mortar for laying DITRA on subfloor

Hello:

Is it OK to use Custom Flexbond modified "crack prevention mortar" to lay DITRA on top of the subflooring? If it is not, what would be best for this application?

Thanks in advance for any help!

 

Hi Moogy,

Custom's Flexbond is plenty good enough to install Ditra if your (unknown) subfloor is the proper grade of plywood or OSB. You could use something cheaper, but, it's only money.

What do you plan to use to install the tiles over Ditra?

Jaz

 

Hi Jazman:

Thanks for quick reply!

(1) I am going to try and place mesh resin-backed 2" x 2" travertine tiles (mesh holds it in 12" x 12" pieces) using LATICRETE LATAPOXY 300 ADHESIVE. All of the thinset bags or mortar said don't use regular mortar on resin backed tiles.
(2) I was debating whether to do anything else with the subfloor. It seems solid with no squeaks, etc. but I had peeled off a layer of pretty old vinyl linoleum and it left a very thin layer of what looks like paper. It's less than a millimeter thick. It doesn't want to come off. If I dampened it first (so it would not suck the water out of the thinset too quick) do you think it's OK?
Any additional advice will be much appreciated!

Thanks,
Moogy

 

Good chance that the paper from the linoleum is over 1/4" underlayment grade plywood. That needs to come out before you begin your installation. Can you see a cross section of the subfloor in a HVAC vent?

 

Dear czizzi:

Thanks for the reply.

I drilled out a 1.25" core from the floor. This house was built in 1975 and all three floors/cielings are made from 2" x 8" tongue and groove Doug fir. The core was 2" thick with the first 1/2" a sawdust//glue composite on top of the 2" x 8" Doug fir.

Please advise on what I need to do to lay the Ditra. I'm disinclined to tear out the composite unless it means the end of the world as we know it.

Thanks!
-Moogy

 

This is particle board and the absolute worst substrate for tile and needs to be removed. You can not tile directly to dimensional lumber (your 2x8 T&G) so you need to go back with a layer of plywood screwed down. Minimum 5/8" plywood or 3/4" OSB.

 

Thanks for the reply. As you can tell I am very much a tile novice so I had a couple more questions:
(1) if one were to lay tile onto the particle board/T&G subflooring, how does it fail?
(2) Is there anything that I can put over the top of the particle board (cement board) and keep going?
(3) The vanity and shower stall is over the top of the particle board. If I want to remove the particle board, how is the best way to do that and cut it along the shower, vanity, etc? Would a compact circular saw work? Tearing out the vanity and shower stall isn't an option.

Thanks!

 

Add any moisture or water spill and watch it swell and disintegrate.

I'm not going to offer any advice on how to make this work, it needs to come out. Rent a toe kick saw and be careful using it. It will cut flush to the item you are trying to take out. I doubt that the partcle board goes under the tub or the vanity Remove the 1/4" underlayment talked about earlier and see.

 

Thanks for the info.

(1) What is the 1/4" underlayment? The attached photo shows a 1.25" diameter plug drilled out of the floor as described earlier in the thread. The photo shows the 1/2" particle board on top of the 2" x 8" T&G subfloor. The bathroom is on one side of this plug and the crawl space under the house on the other. Is the 1/4" underlayment you're referring to somewhere else?
(2) I guess I thought the Kerdi and Ditra would provide some protection against water as the manufacturer claimed.
(3) I guess I'm lucky that the unprotected particle board didn't fail over the last 42 years since installation.
(4) The particle board does go under the vanity but not the shower stall. In fact, it appears as though the entire floor of the house is this 1/2" particle board on top of the T&G Doug fir boards.

Thanks!

 

OK, traditionally, there is a 1/4" underlayment beneath the linoleum - in your case there is not. But regardless, remove the particleboard, add back some plywood and then you may ditra or cement board. Must be the ply buffer between dimensional lumber and the ditra/cement board.