[captsaveahouse]

I just finished putting 3/4in tongue & groove sheeting glued and screwed every 6in on 16in engineered i joist that is to be the sub floor for the second floor of a 24ft by 40ft shop down stairs house up stairs the floor dont seem to be sturdy enough to support tile without cracking. The I joists are 24ft long & 19.2in on center what can I do .

 

[Just Bill]

From your statement, the 3/4 plywood is the only subfloor?? If yes. I would add a layer of 1/2" sheathing, glued/screwed, the 1/4" hardibacker or duroc, per their instructions. That is a long span, and I joists tend to be a bit springy. Usually a rigid floor of 1 1/4 is sufficient for tile.

 

[captsaveahouse]

Thanx just Bill, Do I run the sheets in the same direction but stagger the pattern or cross ways

 

[JazMan]

House,

I need to know the brand & model of your joists, 16" is not enough info. Even then it can be tricky to simply say yes or no. There are many factors including their proper installation. We'll wait for your answer and go from there. Also tell us the type of tiles, size and method and products you are considering.

As for the subfloor, I too recommend adding an underlayment. Make sure it's "underlayment" grade and NOT "sheathing". Sheathing is a cheap grade and is used vertically, outdoors maybe? Underlayments should NOT the glued to the subfloor, are always installed across the joists just like the subfloor and offset both ways. Also the thickness of the subfloor has nothing to do with the deflection of the joists, only the space between the joists, which is where most of the problems start.

Jaz