Old pans and new niches

[gjkilmer]

Just downloaded the book. How helpful! Iam planning to retile our shower using kerdi. Three quick questions.

1. The current shower pan is sound and quite well sloped; do I dare just kerdi over the current floor tile? I suppose I would have to remove some of the old mud layer around the drain.
2. I love the look of John's niches that use a tile as the shelf. However, we are planning to use ceramic that does not have consistent color throughout. What would you thing of epoxying two bullnose tiles together to have a face on both sides but stll be slim?
3. I'm having trouble understanding how the kerdi be lapped with a lap on top on the uphill side. Isn't it like a drainage plane, much like tyvek under siding? While everything will be thin-setted together, is it still possible that drops could roll down to the point where the lower sheet is lapped over the one above it and infiltrate through the thin set between and thus into the wall. I suspect that what I'm suggesting may technically be true but that any possible infiltration would be so miniscule it's not worth a second thought. Am I on the right track?

[cx]

Welcome. Please give us a first name to use.

1. Nope. Even if it were a good eye-dee, time you got a hole big enough to install the drain and pack mud under it properly you'd have most of the floor torn up anyway. And your chances of getting a good, flat, smooth slope for your Kerdi are not good. And how you gonna do the curb and such?

Tear out. Start fresh. Be happy.

2. You could do that.

3. Common concern, completely unfounded. Matters not a whit which direction nor orientation you make the lap joints, so long as the lap is at least two inches. No water is gonna penetrate the lap joint. None. If you fill your shower up to the 15-foot level and let it sit for years, no water is gonna penetrate the lap joints.

And if you try that at home, we wanna see pichers of your shower.

My opinion; worth price charged.

[gjkilmer]

Thanks cx. Name's Greg.
1. Yeah, I had a lot more trouble figuring out how I would retrofit and overlay than just starting fresh.
2. I hope the double bullnose thing will work, I will mock one up and send pix of completed niche if I like the result.
3. I'll buy that. As I was drawing up plans to seal the door and prevent any tampering with my experiment over the next 15 years. I realized that my second floor would definitely not support the weight of the water. Let's see a 4' by 3' shower filled 6' deep = 72 ft3 * 7.48 *8.34 = about 4500 pounds. So sadly, we will have to wait for a willing researcher whose shower is on a slab or something.
Thanks!

[gjkilmer]

I'm planning to cut field tile down to 2x2 or somewhere in that neighborhood for shower floor but this would also have applications for all smaller tile. Does anyone know of sticky sheets of material kind of like the webbed tape for backer board joints that would allow someone to place and space like a 12 x12 group of smaller tiles and then mortar these all at once. What I'm describing here would be much like the sheets that are composed of attached tiles. Not really worth experimenting on my own. If someone already has or knows of a product, it would be interesting to know. It would have to be pretty darn sticky to not cause more trouble than it would be worth. Just curious.
Thanks
Greg

[Tool Guy - Kg]

Hi Greg,
Never done that before, but I remember reading something so I dug it up. Take a look here at this post. It's part of this entire thread.

[gjkilmer]

This is about my third question today.
I have extra hardibacker around anyway.
If I fastened hardi well to my subfloor in the shower, would that allow me to forgo the lath on my preslope?

[gjkilmer]

Thanks. Might be worth messing with those two options.

[Splinter]

Nope... buy a sheet of lath.

[cx]

I've merged the threads I could find for this project, Greg. Please don't start new threads for each question, keep all of them here so everyone can keep up with the background of the project.

And it's helpful if you put your first name in a signature line for all the friendly peoples hereabouts who wanna help.

[gjkilmer]

Okay. I scrapped the Kerdi idea. Too expensive! This is kind of a measly question but what is the point of the roofing felt stapled with the lath under the preslope? It is primarily to prevent the subfloor from drawing moisture out of the mud, right? I have leftover Tyvek that I think would serve the same purpose and save me $20 on a roll of felt. What do y'all think?

[cx]

The Tyvek will work fine. Hell, you can use plastic garbage bags if you wanna.

My opinion; worth price charged.

[gjkilmer]

Just saw a set of pictures where someone used preslope, liner and then mud bed. Then he redgarded the final bed before setting the tile. Is that a good idea? If it worked it would be much like the kerdi system except that the thinset layer and grout would be somewhat lower than the drain and would have to dry atmospherically through the grout. Also, if water got through the redgard, would the bed still be able to drain to the liner and through the weepholes or would it be trapped with a membrane on each side? In a well installed pvc liner shower, is the fact that the 1.5" - 2" mud bed getting wet and filtering down to the liner a big deal or will this method last as long as kerdi where it doesn't get wet?

2. I was thinking of vapor barrier behind the hardi and redgard about three feet up the walls as well as over the bench and the niche? Is this okay or will this really trap moisture?

3. What about redgarding the cement board on the bottom edge up the back about an inch and up the front 6 or 8"? Would that prevent it from wicking where it would come in contact with the mudbed?

4. What's up with the slurry of thinset between the subfloor and the preslope? I've seen some people in this forum suggest it but none of the actual tutorials mention this at all. If y'all think this is a good idea, what consistency makes slurry? Normal thinset consistency?

I'm sure these questions have been asked and answered elsewhere but tracking them down has taken me quite a while. Thanks for all your help guys. CX, you're a saint!

[gjkilmer]

In question 1 of the last post, I realize that only the thinset within a few inches of the drain would stay wet on top of a redgard layer, but is that bad?
Also, can the thinset truly grip the redgard well enough? How long has the product been tested? Is adhesion over redgard an issue at all?

[cx]

1. This is a bad eye-dee. No matter how you do it, you're gonna have water getting into the mud bed at least at the drain because you can't really seal that joint effectively. The weep holes will still drain the mud bed, but there will be moisture in there all the time that never actually gravitates to the weep holes. Can't do any real damage in there, I suppose, but.........

No, there are no issues with thinset sticking to Redgard that I've ever heard of. Been around a long time, but I can't give you a date.

2. Also a bad eye-dee. Yes, it will really trap moisture. It's fine to Redgard the bench and the area around it where there really is no effective moisture barrier behind, but you really don't wanna make a barrier on both sides of the CBU. If you wanna use that much Redgard, just leave out the barrier behind and Redgard the whole enchilada.

3. And make a very nice place for moisture to collect if it is going in the direction gravity dictates? Wicking is not a problem in a properly constructed mud-bed shower pan. There simply is no standing water in that area to wick. It's all on its way to the drain because of the pre-slope. And you will have held your CBU up off the pan liner a quarter to a half-inch.

4. That's for use over concrete floors in lieu of the metal lath you'll have over your plywood floor. Apples and oranges. Doesn't apply to you.

My opinion; worth price charged.

CX, you're a saint!

Maybe you could just add that to your signature line.

Along with your first name, which I've already forgotten.

[gjkilmer]

Finished my preslope last night. Gotta say, looks pretty good! Planning to build a block monument corner bench inside the pan much like in the article by Mr. Bridge. Should I redgard the bench? Whole thing or just the top or not at all. I have a tub for my niche so having to buy it is not an issue.
Thanks y'all,
Greg