Waterproofing tub/shower window niche w/ Hydroban

[chriswand]

I'm hoping y'all can help me out here. I'm tiling a tub/shower surround that has a window in the wet area of the tub. I'm using Go Board as my backerboard and using Hydro Ban to waterproof the seams/corners and fastener heads I'm also embedding Hydro Ban fabric in the wet Hydro Ban for extra insurance in the corners and seams.

I've wrapped the Go Board into the window niche so that it butts up to the vinyl window frame and sealed between the edge of the Go Board and the window frame with Go Board's sealant. But for extra insurance, I was planning on applying the Hydro Ban on the backerboard in the window niche and having the Hydro Ban lap up onto the edge of the vinyl window frame just far enough that it will be hidden by the tile on the sides and top of the niche and the quartz ledge that will be the window sill (which will be well-sloped to shed water).

Does anyone know how reliably Hydro Ban will adhere to the vinyl window frame? On the bottom I was planning on having the embedded fabric also lap up onto the window frame (it would be tough to do that on the sides and top given the tile is fairly thin). Obviously as an exterior window in a shower, there will be some expansion and contraction over time from temperature swings.

I will (obviously) be caulking the tile and quartz window sill to the vinyl window frame with silicone caulk as well, but would like to have multiple lines of defense since I know that water will be accumulating on the window sill from the shower spray.

Thanks!

[cx]

Chris, Laticrete says Hydro Ban will adhere to PVC, and I expect your "vinyl" window frames are similar, so I'd expect your plan to work there. I'd not be as confident of it adhering to the Go-Board pookey, though. Just don't know what that is, except I'm guessing a urethane of some sort.

You might wanna call Laticrete's tech service number.

My opinion; worth price charged.

[John Bridge]

Hi Chris,

I wouldn't bank on the HydroBan to vinyl connection. Instead, use Hydroban on the cement board and caulk between the cement board and vinyl with silicone caulking. After tile and grout you can put another bead of silicone where tile meets vinyl.

That's my opinion. There are others, I'm sure.

[chriswand]

Thanks John and CX for the quick replies!

I did see that Hydro Ban's tech lit said it sticks to PVC, but IIRC it had some disclaimer about that being only as it related to plumbing fixtures. I called tech services and they said they didn't think it would adhere to the window (even though it's the same material, go figger).

Far as I can tell, the Go Board pooky is a silane modified sealant, seems similar to OSI Quad Max (sticky as all get out and about as fun to work with/tool as marshmallow fluff!). I masked off everything except the gap itself before applying, so the Hydro Ban would have to bridge over only a small strip of pooky.

I think I'll end up relying on the Go Board being caulked to the window with Go Board sealant, as one line of defense, run the Hydro Ban slightly lapped onto the window (as a "can't hurt" additional line of defense) and make sure to leave plenty of un-Hydro Ban'ed window frame for a final caulking between the frame and tile/grout so that the silicone caulk has untouched vinyl window frame to adhere to.

[chriswand]

I'm now onto the tile layout phase for my daughter's tub surround. The main field tile will be an 8x16 ceramic subway tile with a horizontal accent of blue porcelain penny round tile. The penny round tile is about 1/10" thinner than the subway tile (see attached photo) before thinset, but I would expect that given the difference in tile sizes, the subway tile once set in a thicker layer of thinset will end up more like 3/16" (or maybe even more) proud of the penny round (since I'll use a larger notch trowel to set the subway tile).

However, I'd like them to flush out so that the finished surfaces are in the same plane. Since the penny rounds are so small, I doubt I can just make up the difference in thinset when setting the tile (like I might with a larger tile) without it oozing through the mosaic mesh and making a mess.

In the past I've set a layer of Ditra to "shim" behind the thinner tile, but the penny rounds are pretty small (about 3/4" diameter), which I don't think is kosher to set over Ditra (with its minimum size tile of 2x2).

So, any suggestions on the best way to end up with flush tiles?

My Plan B approach is to set the subway field tile and leave space for the penny rounds. After the field tile is set, I'ld come back and screed a thin layer of thinset where the penny round will go, let that set up, and then set the penny round with a small notch trowel. Not the end of the world, but more time consuming as well as a bit fussy to screed a fairly thin layer of thinset uniformly enough that it doesn't cause the penny rounds to not lay flat.

Thanks for any creative suggestions--I know I'm not the first to have to tackle this.

Chris

[cx]

I think you're right on point with your proposed solution, Chris. Done alla time. Just make you a screed with a measured depth and use a cementitious patching material or a thinset mortar if the total mortar depth will be less than 1/4-inch. Not an appropriate use for thinset mortar, and some patching materials might be easier to work with in that application.

An appropriate screed might look something like this:



No reason you couldn't use the Ditra, though. The tile size limitation is for floor applications, which are the only applications for which Ditra is designed and indicated. But it would make a convenient way to make a consistent mortar depth if the depth happened to be appropriate. And so long as no one in the Chris houshold is prone to walking on the shower walls, particularly in the accent area, I see no reason it couldn't work. See my warranty information below.

My opinion; worth price charged.

[chriswand]

Thanks for confirming my plan B, CX. The screed approach it is.

Do you have any recommendations for cementitious patching material? I'll be using Versabond to set the tiles so will likely use that (assuming it's no more than 1/4") but my experience has been that screeding modified thinset can get a little sticky, so if you know of other materials that might be easier to work with, I'm all ears!

[Sheldonblk]

Hey Chris how well did the hydroban stick to the go board? I was thinking of using goboard on my walls and using hydro ban on top of my mud bed and up the walls a bit. I really don't want to have to use cement board.

[chriswand]

Casey, the Hydroban stuck to the Go Board just fine. Of course I don't have any ability to vouch for how it will hold up over the long term, but Go Board lists Hydro Ban as an approved sealant (google "go board approved sealant" and the first link that shows up should be a Go Board document listing approved sealants, so I have no reason to think it won't last for the long haul.

I embedded the Hydroban reinforcing fabric in all the corners/changes of plane as well as bridging any joints/seams in the Go Board. Even though Laticrete doesn't require it, I think it's cheap insurance. I definitely would use the reinforcing fabric if you are waterproofing the joint between a mud pan and Go Board walls since that is a prime area for leaks. I also used Hydroban to seal the screw heads from fastening the Go Board to the framing.

I will say that having only used various cement backer boards (both with Hydro Ban and Kerdi membrane) prior to this project, I love using the foam backerboard. Go Board's facing is a non-woven fiberglass and it will make you itch, so wear gloves and a long sleeve shirt, but it is so much nicer to work with, especially for cutouts. And the price was significantly lower than Kerdi board. I, for one, will not be going back to cement backerboard.