1. Is there a special kind of non-rusting staple that should be used? No need, regular staples are fine. 2. Can I simply staple the poly across the top and then let the board screws secure the rest of the poly or should the whole sheet be stapled? If staples are recommended, shouldn't each staple be sealed to prevent water/vapor flow? The staples really aren't a factor in terms of affecting the poly sheet permeability. There's not a vapor drive in a regular shower like you get in an enclosed steam shower with a true steam generator. So hang the poly, slap a few staples to hold it in place, then cover it with the cement board. 3. Once the hardibacker is in place, should the screws also be sealed? If not, why not? (The Hardibacker instructions only say to tape and seal the seams.) If the screws should be sealed, is thinset enough, or use some other type of sealant? Screws don't need to be sealed. The vapor barrier is behind the face of the hardie so there's no need to seal anything on the face of the board like the screw holes. Any divot where the screw head is will get filled with thinset when you tile. 4. Should the poly be sealed across the tops and sides with some sort of sealant? If not, why not (wouldn�t the water/steam simply go around these unsealed ends? No need. Again, it's not a steam shower where all six sides of the steam shower cube need a tight and integral vapor barrier. We're really just worried about water on the walls getting through the tile/grout, be it through penetration/absorption, through pinholes in the grout, cracks in the grout or tile, etc. In a shower surround I usually hang one sheet of 6-mil plastic and wrap it around the walls, from one wall to the next. Leave it a little slack in the corners so it doesn't get stressed/stretched when you hang the tile backer board. 5. For the area where the poly overlaps the tub flange, again I assume a sealant should be applied between the tub flange and the back surface of the poly. Yes, you can run a bead of sealant or caulk on the flange then bed the poly into the sealant/caulk. That'll hold it secure to the flange. Then cut the excess off with a utility knife. 6. What about the plumbing pipes? Will a good bead of sealant all around be enough, or is there some technique for this area? No worries, again, this isn't a steam shower where you have true vapor drive. The shower arm hole will be covered with an escutcheon plate and it'll be above the splash zone. The trim plate that covers the shower valve usually has a gasket on the back of it, when you install it it seals the trim cover tight to the tile so no water can get through the valve trim and into the wall. 7. EXACTLY what type of sealant should I use? I've seen references to using asphalt tar, silicone caulk, acoustic sealant, Kerdifix�.? Can acoustic sealant be bought at HomeDepot/Lowes/Menards? I usually use a urethane sealant when I'm looking for a sealant. For caulk, usually a silicon-latex will work fine. 8. Should you use the same type of sealant on the poly/tub flange area as you would on the other edges of the poly? Really no need. Just seal the poly to the tub flange to help hold it in place. 9. Here is my major puzzlement: I keep reading that a bead of caulk should be run between the installed poly and the cement board at the bottom of the tub flange. Wouldn't this trap any moisture between the board and the poly?? How can the water run back into the tub if there is a line of caulk blocking the path? On the other hand, if it is left unsealed, how to you prevent water from the shower area getting on the end of the board and wicking up the board? (Or is it irrelevant that the board gets wet because of the poly barrier?) It's a confusing area. You can seal the poly to the tub flange, it's not necessarily a "seal", it's more just tacking it in place so it doesn't slide around. That's really the only thing you have to do at the tub flange, is make sure that the poly is overlapping the tub. After tiling, a lot of folk will caulk the tile to the tub. Some caulk the entire line, some leave a few areas open as "weep holes", some don't caulk it at all. Whatever moisture gets through the tile and grout then hits the cement board. The poly prevents the insulation and framing from wicking that moisture out of the cement board and into the framing cavity. What usually happens is that during a non-showering drying cycle, the moisture that got through the tile and grout leaves the wall through the same path it entered...through the grout, the tile, the cracks and crevices, etc, and goes back into free air within the bathroom. If you do get excessive wetting in the cement board, then yes, liquid droplets can form on the poly. They'll run down the poly, or down through the cement board, and theoretically drain back in to the tub over the tub flange. Sealing the poly to the cement board deosn't do any good that I see. WEre you to ever get excess amounts of water in there, moisture down there will just wet the cement board and excess moisture will then just drip out the bottom edge of the cement board. That's why some folk leave weep holes or gaps in the caulk if they caulk the tub-to-tile line, or why some installers don't caulk it at all. Still, most people want the tile caulked to the tub, and that's fine, I have no reservations about doing that at all. Some people envision water building up back there...realize that if there were excessive water, it would saturate the cement board, then the grout would appear wet, and the grout would dry with the moisture going back into the bathroom air. It sounds a lot more serious than it all is. You need a seriously compromised wall to get water collection on the back side of a tiled wall. 10. What about the ceiling � My plan was to leave the existing drywall/greenboard up there (I haven't started demo yet, so I don't know exactly what it is.) Does this need to come down to studs + have poly barrier there also? If not, why not? Wouldn't steam simply absorb into the ceiling and go through to the studs? Again, it's just a shower, not a steam room. If it's in sound condition you can leave the drywall up there and just paint it. The paint film itself can act as a vapor retarder. 11. As for the plastic itself, as long as it is 6 mil, does it matter what "kind" it is? Home Depot only had one type, and it just says "plastic" on the label, which no indication of if it is poly or not. Do I need to find something particular? 6-mil polyethylene, or "PE" sheet plastic. They normally sell 4-mil and 6-mil, use the 6-mil, and it's usualy PE. 12. How far past the edge of the tub/tile area should the poly and hardiboard extend? It usually stops at the edge of the tub under the last column of wall tile. The wall tile hides the transition seam between cement board and drywall. 13. Should I use alkali-resistant tape and thinset at the seam where the hardiboard meets the existing drywall, or regular fiberglass tape and drywall compound? I use paper tape and joint compound with drywall. I use alkali resistant mesh tape and thinset on cement board. Since the transition line will be covered with tile, I use mesh tape and thinset at the cement board/drywall transition seam. One extra tidbit: If you thinset and tape the seams between the cement board panels on one day and then tile the next, one big mistake people do is they leave too much thinset buildup on the seams, you end up with humps. The seam should be flat. It might even help to tape and thinset the seams as you're tiling the wall.

Bill - The last "fix" was the same as 2008's - put more screws in, reset the (cleaned up) tiles using Flexbond this time. I know I should have taken your advice and insisted on tearing it all out and doing it right, but when he started it seemed like a small area (when he left the first day I found about 10sf more that just pulled up, made him come back the next day and reset that too). But I really didn't want the hassle and my lawyer said to "work it out" rather than suing. Now I'm wondering if there's anything I can do in the basement to stiffen the floor so we can make this job last and won't have to move the appliances, tear out the tile, and move out of the house for 2 weeks to fix it. Can I add more plywood b/t the joist underneath, screw the panels up into the existing subfloor so no banging from hammers? Will that help at all? Or cover the joists (and insulation) with sheets of plywood spanning the joists? Might not be able to do that everywhere since ductwork and plumbing hangs below in some areas. Ironically, the worst (heaviest traffic) place in the kitchen where all the tile to date has come loose is right near the center of the house where we have lally columns and doubled-up 2x10s, so that *should* be stiffer than the middle of the room (13 ft span, blocked about halfway). The foyer tile has just failed all over - I only have a small corner by the stairs and in the coat closet that hasn't already been reset. Thanks.

Oh, I really feel for you -- after all of that work. So discouraging. I am sorry I don't know the answer. I would recommend joining and posting on the John bridge forum (johnbridge dot com). They are an excellent resource.

Thanks for all the input. I might not have been clear enough in my original post. The 1 x 6 planks, though intact, are pretty old and there is a little bit of rot around the toilet. This house is more than 60 years old. The plumber is just concerned that the joint esp. between the tub and the finish floor, no matter how you seal it, will allow some moisture to escape through and cause damage to the already old plank subfloor below, which might fail under the weight of the new tub. We were considering an underpayment on top of the subfloor and putting linoleum over it. This is actually the reason I was hoping to put the tub directly on the subfloor so that the thickness of the underlayment will cover the joint at the bottom of the tub since linoleum is not thick enough by itself. My intent in the original question was to "reinforce" the old subfloor using a thin layer of exposure 1 grade plywood and set the tub as well as the underlayment for the linoleum on top of that.