My kitchen remodel job is in a late 70's built ranch style house. The floor is post and girder construction, 1 1/8" plywood over 4" x 6" girders at 4' on center.
The owners have their heart set on a certain 20" square tile. In my opinion, there is too much deflection in the floor for tile. I told them that I could either pull the plywood and install intermediate joists OR I would just glue and screw 3/4" plywood over the existing 1 1/8" ply, running in the opposite direction. However, if they went with the cheaper option (no extra labor charge, only plywood cost) of the ply over ply, I wouldn't guarantee any cracking in the tile or grout. The area in question is approximately 9' x 9'. My recommendation to them is to add the extra joists, of course. But, with a $500 price tag, they are a little hesitant.
Any help, suggestion, advice you pro folks can turn my way? With the small area, will the ply over ply, totaling 1 7/8" in thickness, give enough resistance to deflection at 4' on center?
Thanks very much for your consideration.
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