waterproof and screw size

Help, need quick answer; behind on job.
If I want to be on safe side and waterproof the tile bathroom floor, where do the membrane film need to be located?
Between the hardie bd and plywood or plywood and subfloor 2x6.\?
Screw: Do I screw the plywood to the sub floor all the way thru the 2x6 subfloor or just penetrate be fine?

Hardie bod: Do I scre the hardie board to plywood and thru the subfloor or just enought to penetrate the sub floor?

Waterproof membrane if uses: How do I attach that to the plywood? Can I use the same screw that I screw my plywood to the subfloor be ok?
Need answer ASAP: Need to run to HD tommarrow. Need to finish this job. Just cut all my plywood.
Really appreciate if I get some good advices.
G

This is your own house is it? You're behind schedule and the wife or gf is on your case? Do you think you really need to waterproof the bath floor?

Jaz

Tileplayer you really need some more research before you retro-boost into this job. Is this your own home and are you sure the floor joists are 2X6's?

My wife and also my daughter coming back in Dec.
Only got one toilet at this moment.
It's 2x6s tongue & groove DF. Span is approx 4'-9" between the foundation wall and the first 4x6 joist. And also installing 15/16" plywood with thin set then cement board. I like to provide a extra protection.
I want to install a waterproof membrane over the plywood and then thin set. To prevent accidental spill water and leakage down to the plywood and cause mold.
Can you give me a name of a film that I can lay over it other than roof paper?
If I use this film, do I just use the same screw as my plywood, or staple separatly? Too much holes?
Since the thin motar as I understood it is to fill the void, it not need toattach to the plywood, correct?
That bring up a extra question, why put anythig under the cement board since the plywood is really nice and sanded. (There is no void, so why a cement board need the thin set to sit on?)

George, there is nothing you can use to waterproof the floor that would be under any of the layers but the tile. All those screws would make it nothing but Swiss cheese. Going back to your first post, make sure the 2x6 subflooring is secure to the beams.

Next, install your plywood using coated screws, deck screws work great, fastening every 6" around the perimeter of the sheets and every 8" within the field, but go in straight lines to eliminate any bowing, don't fastening the perimeter and then filling in the field. 1/8" gap between sheets and 1/4" gap around the room. Lowest quality plywood would be CC plugged and sanded, never seen it, though, around my area, BC sanded is it. I hope you didn't buy anything listed as "CD exterior" or "sheathing rated" because that's not enough quality under ceramic. Since you've already cut it, if you didn't get the right stuff, the wrong stuff is good for basement or garage shelves.

Then you can install your choice of either cement board set into a bed of thinset or use a tile membrane. Pretty much no company is going to warrant their products over pier and beam structures, but we see posts often enough that I can only assume it works because I've not ever seen anyone come back to complain about cracked grout or tile. Almost 2 1/2" of wood and ply is a thick floor with only a 4 1/2' span. Bet you could drive a truck over it and not feel any bounce.

No need or use for thinset under your plywood.

You do need thinset under your cement board though. Why? Unlike wood, where when you start to go from the first piece into the second and the first panel rides up the screw shank a tiny bit (called screw jacking), when the head of the screw reaches the panel surface, the two pieces get pulled together tightly. With cement board, you have the cement dust/concrete tear out between the two and the screw head stops at the surface, it doesn't pull all the cement tearout down into the plywood below. With that, you now have unsupported voids throughout the cement board installation. The cement board will fatigue and flex in those voids in time causing tile and grout cracking.

If you insist on having the floor waterproofed, go with a membrane instead of using cement board. Membranes cost more up front, but in general they outperform cement boards and have the added benefit in most cases of providing waterproofing as well. You can use cement board if you wish and then cover it with a trowel on waterproofing membrane, such as Laticrete's Hydroban, but then you will end up with a floor that at a price per sf cost more than the sheet membrane $ per sf and took 4 or 5 times as long to get installed and waterproofed. Look into Schluter Ditra which is waterproof and the seams over 1 meter would be made watertight by going over them with Kerdi band (Schluter's shower membrane) or look into Noble company's Nobleseal TS. Both of those sheet membranes get applied using thinset and add only 1/8" or 1/16" in additional floor height respectively.

Thanks for the reply BlJ: Since I got the plywood (Exposure1, and look really sanded and nice. Can say but it look A-C one side is very smooth, other few knotts) cut and the Hardie board (1/4") cut; I may not try to waterproof it since the membrane would be all torn by thinset anyway. (The other way as you indicates would be toocostly and more work). If I have known, I would have start out with difference system what you suggested.
I'm using Versabond thin set both under the Hardie and for the tile. I hope I have enought time to install the thin set and screw the Hardie down before it set.

Sorry, but I found on your forum indicating that I need to waterproof all plywood surface. Now would the cement board really protect the plywood it sit on? What if I put a poly mill vapor sheet under it and screw in with the plywood screw? I know it may get torn but it may not too. Would that work? In that piece I read, they say I could put a waterproof over the cement board then thin set. (Either way)
What do you think, or for a batrhroom would I have that much problem other than mopping the floor or a toilet leak?

Versabond will be fine over and under. You'll have plenty of time to comb the thinset, set the board and screw it down, make sure to use the robertson (square drive) backer screws, not the phillips head screws and don't attempt with a battery operated drill. Give the bucket an occasional mix to keep it fresh and you'll get a couple hours out of it. Just mix half a bag at a time.

Get the idea of the poly sheeting out of your head, Got it?! You're over thinking it. At this rate, it won't be done be the time the wife and daughter get there.

Install your toilet so it doesn't leak. Frequent damage I've seen had been caused by a lack of caulk around the base allowing condensation on the tank to drain down along the sides and run under the base. Other damage was a leaking supply line or leaking at the bolts connecting the tank to the bowl or the gasket between the tank and bowl that is closed off when the flapper goes down. That kind of leaking is easy to see and gets neglected by homeowners all the time. Unless the sewer line is backed up, there is never any water around the wax ring except when flushed, a toilet trap is upside down, there's nothing but air between the water you see in the bowl and the wax ring.