Ask Me Help Desk - Is my bathroom subfloor going to be okay?

:confused:
I need to lay a sub floor in my bathroom and I know very little...

Our floor needs to be very sturdy because we are laying 1" hex porcelain tile and a 400 lbs. cast-iron, clawfoot tub (with water and extra-chunky person, yer talking 2200 lbs. or so, I think it came out to).

I reinforced all the joints under the feet of the tub with two layers of 3/4" plywood (both sides, four in all) using Heavy Duty Liquid Nails and 3" nails. On all other joists, I just put 1 layer of 3/4" plywood on each side (2 in all) same procedure.

I was planning on using only 3/4" plywood as my sub floor because my tile guy is going to pour a 1" "mud" floor to make my it level; I assume this is also to reinforce the floor as well?

My questions are such:

Will my sub floor suffice as I have described it?
Should the seams of the plywood run parallel to the joists?
What kind of screws should I use? what size?
What should I use to glue the subfloor down, Liquid Nails Subfloor Adhesive?

Thank you for your answers

Gangelo...

I use a 3/4" tongue and groove plywood for my subfloors. I run the plywood so that the 4 foot seams end up on joists and the tongue and groove run perpendicular to joists where they can join and span the joist bay with support between plywood pieces.

Use liquid nails subfloor adhesive on joists and on the tongue of the plywood.. then install butting pieces together, but leave about 1/16" where plywood joins. I would then use 2.5" screws to screw the floor down being sure to grab the joists every 8" or so.

Then I would run 1/2" plywood perpendicular to 3/4" plywood being sure to place adhesive bewteen layers (so 1/2" runs parallel to joists now) and screw that off every 8 inches with 1-1/4" sheetrock screws (grabbing the 3/4" underneath). Be sure to grab the joists with some 2.5" screws along the joist as well.

I would do this just because you have so much weight and a 1" pour of cement with such small tiles.

Not everyone will agree with me here...;)

Anyway... that's how I would tackle this one...

Let me know what you think...

MARK

Quote:

Originally Posted by massplumber2008

Gangelo...
...I would run 1/2" plywood perpendicular to 3/4" plywood being sure to place adhesive bewteen layers (so 1/2" runs parallel to joists now) and screw that off every 8 inches with 1-1/4" sheetrock screws...

Mark, ty for your answer. I was basically told the same thing by someone else... three questions please:

Regarding the adhesive between plywood: do I need to cover the ENTIRE plywood BETWEEN layers with the adhesive or just kind of run "beads" evenly spaced out?
Regarding the 1-1/4" screws, do I screw by the seams only, or, in a "grid" pattern?
How far do I want to place my subfloor from the studs? Someone told me 1/4" for expansion?

** I forgot to mention that part of my subfloor (around the perimeter on two walls) has some of the old wood flooring that runs perpendicular to the joists. I need to leave these in place to hold up two non-weight bearing walls. One area is about 5 inches depth and the other about 1-2 inches in depth. I cut them off at the middle of the joists they are supported by so I can butt my 3/4" plywood up against it. There is also one place where prior plumbing notched out some of the wood floor in to the joist it rests on, so there is not a gaping hole per se.

I guess the problem is that the wood floor is not exactly 3/4" thick; how do I properly "shim" the floor up to meet the 3/4" plywood I will be laying down?

The other question, is what is the best method for "filling" the hole the old plumber notched out?

TY so much for your help!

1) lay adhesive down every 8-10 inches in strips.

2) Screw in grid pattern.

3) Someone told you correctly... 1/4" should do it.

The difference in height between old floor and new floor can be resolved with a floor patch compound feathered to about 12" wide... let dry, then apply adhesive every 8-10 inches and set 2nd layer of plywood over all.

The hole in floor plumber notched out should be covered by the second layer of plywood. I would not woory about patching it if it is just a 6 inch hole. Anything larger than that I would patch by spanning hole with some 2"x4" and screwing through floor to catch wood then apply patch.

Let me know if I understood all...

MARK

Yes; that is it; thank you much!