Sealing Hardi backer and glass block window

[TJfive0]

I am putting a ceramic tile surround in my bathroom around my tub. I am doing it from the tub to the ceiling.

I have a glass block window in the shower/tub area.
I have installed hardi backer board everywhere thus far, except the ledge that meets the glass block window. I am not sure how to handle this ledge as it is only about 1 inch thick.

I know it would have been ideal to have the glass block window flush with the tile, or have a larger ledge, but this is what i have to work with.

Should I install the thin strip of hardi for the 1 in ledge to meet the window with the rest of the hardi backer?

How do I seal between the window and the hardi on the walls?

As for the rest of the seams, should I use alkali mesh tape then thinset over the joints? Do i mesh tape and thinset in the corners as well?
Then should I paint the entire hardi backer shower area with some water proofing compound like red guard? If i do apply redgaurd, should I apply it a 1/4" or so up the window from the hardi to make some type of seal?

Then apply my thinset and tile?

[Kman]

TJfive0 said Should I install the thin strip of hardi for the 1 in ledge to meet the window with the rest of the hardi backer? As for the rest of the seams, should I use alkali mesh tape then thinset over the joints? Do i mesh tape and thinset in the corners as well? Then should I paint the entire hardi backer shower area with some water proofing compound like red guard? If i do apply redgaurd, should I apply it a 1/4" or so up the window from the hardi to make some type of seal? Then apply my thinset and tile?

I would say yes to every question except one: Don't put redgard up the window. I would install the hardibacker, then run a bead of quality clear silicone around the joint where it meets the window. Apply redgard all around up to the shower head height and up to the silicone bead on the window.

Check the redgard instructions on Custom's website. The first coat of redgard is diluted with water (can't remember the ratio off the top of my head), then full strength on the second coat. Make sure you cover every square inch thoroughly, and if you have any blobs of excess be sure to flatten them out before they dry. Removing them after it's dried may cause you to have to re-apply for that area.

For that 1" strip on the window ledge: that's always a tough one to do without breaking the hardi. Their instructions are to use thinset underneath in that application to fill in any voids, however it's not likely that you'll be putting enough pressure on that 1" strip to cause a problem, so this is what I do. Keep in mind that this is against Hardi's instructions, but I've done it before and it works.

Liberally apply a bead of construction adhesive to the back of the Hardi strip, push it into place, and secure it with a few finishing nails, preferably from a nail gun. I find it necessary to hold down the ends while I shoot a nail in a couple of inches away. Holding down the ends keeps them from kicking up and snapping off. As long as you keep it from breaking apart while you put the nails in, the glue will dry and hold it firmly in place. Wipe off any excess glue, let it dry, then apply mesh tape and thinset over the joint.

If you're like me and need some pictures to look at, my website has a couple of pages with something similar to what you're doing (sans window). I used Permabase and Laticrete 9235, but otherwise the process is the same.

Preparation for Tiling a Shower or Tub Surround | Welcome to Trevathan Floorcovering

Tiling a Shower or Tub Surround | Welcome to Trevathan Floorcovering

[Sean Moore]

Should little ledges like that have a fall to them to shed water or can you do them flat as long as the silicone is good? I've done one glass block windowed shower (scared but it was for a relative, 5yrs = no problems so far) in travertine (scared me even more) and had a ~2in ledge. I gave it about a half inch fall and she sort of complained because she couldn't put her shampoo on it reliably anymore.

Oh, and the old sill was flat and I had to do some framing repairs because of water damage... therefore I put some fall in the new one.

[TJfive0]

Thanks for the response!!

When you apply the thinset to the seams do you......

Apply thinset in the joints, then put mesh tape, smooth out, let cure, then put another layer of thinest over the tape and feather it out like you do on drywall?

Or do you just apply thinset to the joints, put mesh tape, smooth out, let cure, then apply waterproofing?

[TJfive0]

Also....

I used a mix of screws and galvanized roofing nails to secure the hardi.

Should I do a skim coat of thinset over any of the nails or screws that appear to not be completely flush?

And If I do do this, do I skim coat it before or after the red guard waterproofing?

[Kman]

A tiny bit of slope on the ledge won't hurt (about 1/16" is fine). Considering it's 1" wide, it's not going to hold much water. The best thing that can be done for that ledge is for the user to wipe it off with a towel after each shower.

For the nail/screw heads, just skim over each of them with thinset, let it dry, then Regard over them. Redgard adheres much better to a cementitious surface, as opposed to a nail or screw head. A depression in the wall from a screw that is counter sunk will cause some excess Redgard to build up then start running out. That usually happens after you've left to room to let it dry, then you've got a big drop of Redgard to scrape away.

For the mesh tape, skim a thin layer of thinset over the joint, embed the mesh tape, then skim it again. You want the tape thoroughly embedded, but you want to avoid having a bump in the wall at each joint. This is why I use permabase. The factory edges, (the long sides anyway) are tapered to allow for some thinset buildup. Makes for a much flatter wall.

[TJfive0]

This would be unmodified thinset correct?
Any particular brands preferred, or any to stay away from?

[Kman]

If you're going over Redgard, you can use modified thinset. It'll give you a better bond and more "working" time.

You'll probably be limited to the brands available in your area, but at Home Depot look for Custom Versabond. At Lowe's, look for Laticrete Multipurpose or Mapei Ultraflex 1 or 2.

If you have a particular brand available that you want to now about, let us know the name of it.

[TJfive0]

So I should use modified thinset on the hardi backer with the mesh tap, as well as modified thinset over the redguard to apply the tile?

[Kman]

TJfive0 said So I should use modified thinset on the hardi backer with the mesh tap, as well as modified thinset over the redguard to apply the tile?

Yes, that will work just fine.

[TJfive0]

If I create bumps, or some areas aren't completely flat, can I skim coat those with the Versabond to make them flat, then apply the redgard?

Say I skimmed nearly all the wall, that would be fine correct? The redgard and subsequent tile would adhere no problem right?

[Kman]

TJfive0 said If I create bumps, or some areas aren't completely flat, can I skim coat those with the Versabond to make them flat, then apply the redgard? Say I skimmed nearly all the wall, that would be fine correct? The redgard and subsequent tile would adhere no problem right?

Yes. Let the thinset dry overnight before applying Redgard, longer if the thinset is more than just a skim.