Also, a slow cure time might be a good thing. Give it time.

I bet the thickness is causing the problem with drying.

(and this is the man who made fun of me for gluing a taillight lense together?)

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I bet you're right.

My desire to use the mastic is not based upon saving money...........I thought it would be preferable for this task.

Clearly, the thickness of the mastic and the product itself is not a good combination here. We'll give it a week and see if it will finally setup.

Personally, I would've put some hardibacker board on top of the plywood and thinset to that. If redoing it is not an option, and you just want them to stick dammit, then I'd just pull the tiles and use Liquid Nails/subfloor and shim them to height. Throw a short level across the span, measure (-the tile thickness), and glue them down.

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1984 300TD

That was my thinking too.

Thanks for all the help.

If the mastic doesn't dry, I'll use some shims with the Liquid Nails.

I'm going to give it a few more days before I give up on it. The first batch dried to an acceptable level after one week.

We tile floors all the time with "polymer fortified thin-set mortar" I think its called. I just buy the bag I recognize! The instructions are very clear that it is perfectly fine for use on plywood, backer board, concrete, etc. I generally like to use "underlayment" plywood. No voids. Floor shouldn't deflect when walked on. Experience has shown that fastening the new underlayment subfloor with lots of screws from the collated screw gun usually does the trick.

Unfortunately Brian the only real solution is a new reinforced subfloor that will not flex. Anything else is just not going to hold up.
RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

That's not a bad idea but I'd recommend the polyurethane construction adhesives. You have a lot more working time and they set up, unfailingly. It's like super glue: water vapor is what catalyzes it and it gets enough to do the job while being spread out.

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1986 300SDL, 362K
1984 300D, 138K

I just had an idea! How about 3M 5200? Tenacious, waterproof, slightly flexible. Might be perfect. RT

__________________
When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

Yep, I know it Rob. I'm just buying time. I'm just not in the mood to rip out all the tiles and start again. The marginal single sheet of plywood lasted 15 years and most of it is still intact..........despite the noticeable flex in the floor.

Thanks for the tip about the polymer thinset.