Silicone will adhere to just about anything with great force. You don't need to overthink this or overspend on the subsurface. Plain drywall was used for years with zero problems. The problems with any sheet surface for a wet area come where the seams are. And where the top caulking usually fails. There is where the corner bead of caulk needs to adhere tightly. And that's on top of the surface, in the corners, not underneath it. So, choose whatever you want for the substrate, but be sure the corners are clean, and that you use a new tube of caulk for the corner beads.

What kind of screws did he use ? I'd ask him (or print out ) the install instructions for DensShield. - I'm pretty certain you'll find language that says something like : do not use drywall compound ! This is the manuf. instructions and needs to supersede any and all of his experience, intuition, and "I've never had problem yet doing it this way" A larger issue that no one has touched on is the Redgard over this stuff. RG will protect the screws and drywall mud from moisture ( if he applies it thick enough - he won't . Ask him if he has wet film gauge or even knows what one is) -but- I'm not sure RG will play nice with the acrylic coating of the DensShield. It may, but it's not an accepted assembly and really shouldn't be considered. Let him test it on his everyday shower. And don't let him tell you he has. Those products haven't been out long enough for him to have dreamed up this concoction and have a twenty year test bed from which to evaluate their compatibility and performance. Neither company is going to warrant the shower used as such. If he's so confident , and you still want to roll the dice - have him purchase a performance bond for this frankenshower.

How is he waterproofing the screws that hold up the board ? Does he use a wet film thickness gauge to determine if his seam sealer is thick enough? Does he even know what a wet film thickness gauge is ? Its a cheap and fast way to do a shower , not a good one particularly. You're basically putting drywall in your shower. Does that sound good to you ? Screams tract house production builder that will be outa business in the next downturn.

More research...and estimates of cost. 1 wall 39" x 60", 1 wall 65" x 60", 1 pony wall 39" x 15", top of pony wall, 4" x 39". Durock- $155.00 panels 5 = 75 sf = $65.00 Screws 180/ $10.00 Fiberglass mesh Tape $8.00 (1 roll, may need 2.) Thinset adhesive over tape. $30.00??? Type 1 organic adhesive or latex modified thinset mortar Liquid membrane $55.00/gal (will 1 gallon be enough?) Kerdi membrane (plus Durock or drywall first??). $373.00 + (more work taping.) Kerdi membrane 75 sf $163.00 Kerdi screws 2 boxes? $25.00 Kerdi inner corners 2/ $13.00 Kerdi outer corners 4/ $26.00 Kerdi shower arm $8.00 Kerdi faucet $8.00 Unmodified thinset mortar $30.00???? Kerdi board (plus Durock or drywall first??) $379.00 + Kerdi board 6 = $222.00 Kerdi band $38.00 Kerdi screws 2/ $25.00 Kerdi fix $25.00 Unmodified thinset mortar $30?? ?? Kerdi inner corners 2/$13.00 ?? Kerdi outer corners 4/26.00 Wedi board tub surround kit $575.00 5 – 3x5 panels 10 oz joint sealant 1 box washers 100 ct 1 box screws 100 ct 2 flexi collars I know kerdi board says it does not need a backer board or drywall, but I am not sure about that. It also says it can go in front of drywall. Really don't like that. Do I need to waterproof the back side of the pony wall, too? Or just the tub side and the top of the pony wall? Did I leave anything out of the materials list? I couldn't get a price on the unmodified thinset so I guessed. Laticrete Hydro Ban boards- $???? Look like they are as easy to install as Wedi boards. Couldn't find any prices. Wedi might be more expensive, but it is easier and faster to do if I can't find a contractor who has used it. Even with no experience with it, surely he could install it. Maybe?? If he won't, then it will be a DIY situation. Has anyone used Hydro Ban boards? Are they as easy to install as Wedi? Thanks.