Stupid floor buckle....

[mrcaptainbob]

Nearing completion of Wife's bathroom. The floor is sistered and leveled floor joists, covered with two layers of 3/4 ply run n/s 1st layer, then e/w 2nd layer. Glued and screwed. Hydronic floor heat was also installed on basement side. Luan was cut to fit and glued down with Elmers wood glue. Sticky-back tile layed down and paint and molding in place along with appliances. So...two/three months later and the dang floor has a bubble of sorts in it! The luan came free from the 3/4 ply subfloor!! RATS!!! I do not think I can squirt glue from the underside. I considered a Forstner bit with a gauge block to drill through 1 1/2" several places, but don't think I can get...liquid nails?, some better grade wood glue?... up in there and smeared around. I'm thinking I may have to remove appliances and rip that stupid 'bubble' out and replace it all. RATS!!!

[mrcaptainbob]

To repeat...sistered floor joists (glued and through bolted every 18" in W pattern). Leveled floor joists. 1st layer of 3/4 ply layed n/s and glued and screwed to floor joists. 2nd layer of 3/4 ply layed e/w and glued and screwed. Dimension from floor center to concrete basement floor has not changed in well over eight years. My plan is to set ceramic tile now. Since the floor is rock solid can I use backerboard and trowel grout and set ceramic tile on that? Since there is hydronic floor heat in this room there is some expansion/contraction between summer and winter. Will this cause any upset in the tile or backerboard? Should I fasten backerboard to the plywood subfloor or let it float? Come to think of it, floating may not be possible, as it would be held in place by toilet flange and shower drain.
Any suggestions?

[HayZee518]

other than using steel support joists, you're gonna get some flexing in a wooden floor. make sure your sistered joists are installed "cup side" up. This way any axial load goes out to the joist ends. For your backer board, screw out from the center to the ends (just makes sense) Wait for at least two whole days for the adhesive to cure, THEN tile and do what you have to.

[mrcaptainbob]

When I sistered them up many years ago (10+) I did cup them up. I also placed a mark at the center of the room on one of the joists. Took a dimension from that to the basement cement floor. It has not changed at all in that time. I do understand that you may be alluding to movement while using. Well, I'll just have to go with the ceramic and see if that works. You mentioned glue. Is that backer board glued as well as screwed? What kind of glue? I was surprised that the liquid nails gave way when the floor heat came on. It had four months to have cured between the luan and the plywood subfloor. What kind of 'glue' should I use for the backer?

[HayZee518]

the newer types of adhesives should be looked into. Older stuff was latex or water based. A solvent based adhesive evaporates the vehicle faster than a latex, even though water based seeems to dry out faster. Loctite products are safer and more durable. Check "Liquid Nails" products and get industrial brand. If you drive a fastener into steel you must pre-drill a pilot hole before power fastening a screw type of fastener. These are usually of the torqs type with a star bit.