I put down 1/4" Durock Cement Board on a new 3/4 plywood subfloor for my bathroom after the toilet leaked onto the original particle board and it rotted. We found that out after my wife put her leg through it! (how in the world particle board even meets code requirements is beyond me) I screwed the cement board down extremely securely, then realized I never put any adhesive at all on the plywood before I fastened it down. I now have taped on all the joints. I haven't put any tile down yet. Is it imperative that I unscrew everything and put some thin set down, or am I gonna be ok without it??

As I mentioned above, I put in a brand new 3/4 plywood subfloor,followed by 1/4" Durock Cement Board(next gen?) and it feels and looks pretty even. I hate to have to take the half ton =0) of screws I put down, just to put the mortar down and then redo all the screwing and taping of the cement board.

I am putting down 12x12" Ceramic tile using Mapei Ceramic Tile Mortar. (Polymer-enriched Thin-Set Mortar, if that matters. I noticed many people asking for help here didn't give enough info up front for a good answer, So trying to be specific as possible)

Also, I'd rather not mix the entire 50 lb bag of mortar at once, as I have another project to do in the near future and the bathroom I am doing is only 35 sq ft. Is there a ratio of water to mix (For example,1 part water to 4 parts mix) that I can use so I just use about half the bag? I would just weigh out 25 lb of mix and cut the water in half, but I have no scale of any sort here to weigh it.

Hmm, Maybe I need to invest in a scale after my wife put her foot through the floor! (Lord I hope she doesn't see this! LOL! )

You should have no problems by leaving the Dur-a-lock down without gluing it to the sub floor.

I mix to a consistency of soft mashed potatoes.mortar has to grab tile. Do not mix enough to do whole floor. Usually make 2 batches for room that size.

Chuck

Hi Pilot,

I don't know about Dur-a-lock, but Durock and all CBU's require a leveling/supporting bed of thin set mortar under them. It's not to glue (hold) the board to the floor, it's to support every square inch so there is no movement.

Will it fail? I guarantee the tilework is liable to develop hair-line cracks in the grout. When, I don't know, but usually within 5-6 years. You may never see the cracks, or it could happen by next spring and some grout could come out in chunks. Will the entire job be a failure? Probably not.

I never mix #50 of thin set at once. Every bag gives you an approx. ration, do the math and then tweak as necessary.

Jaz