Kerdi Membrane Installation Quick ?'s

[userbob]

I have a shower with a bench in it that I built. The shower is rectangular in shape and the bench runs the length of the shower on one end. When I put up my Kerdi membrane over the walls, how should I handle the bench?

Do I use one piece that runs from the ceiling all the way to the floor, following the profile of the bench?

Do I run two pieces: 1. ceiling to the inside of edge of the top of the bench, 2. top surface of the bench all the way to the floor, following the profile of the bench and using Kerdi band for the inside edges?

Do I run three pieces: 1. ceiling to top of bench, 2. top surface of the bench, 3. front surface of the bench and then use Kerdi band for the inside and outside edges?


Also, how should I handle inside corners where two walls intersect? Do I do it like wallpaper and stop pieces at the intersection and start a new piece with a slight overlap or should I just just continue the membrane to the adjoining wall?

[Tool Guy - Kg]

Hi Zeke,

Kerdi membrane becomes waterproof at the seams when there is at least a 2" overlap of membrane. To reduce the thickness at the seams (from overlapping standard Kerdi Membrane), KerdiBAND is used to cover the seams. It is half the thickness of Kerdi and comes in handy rolls that are 5" wide.

How you handle the orientation and how you cut pieces for each section/wall or how you continually wrap around corners is up to you. But if this is your first time, I'd suggest NOT wrapping the Kerdi around inside wall-to-wall corners as it's tough to not get excess thinset trapped in the corners. Sheets of Kerdi that stop in the inside corners (vs. a continual wrap) gives the thinset a place to escape as you're embedding it with your drywall knives.

And you should purchase, if you don't already have them, pre-formed "Inside Corners" and "Outside Corners" to handle corners where three wall planes intersect each other.

do you already have your thinset purchased? Can I ask what you have and what you're using for a substrate?

I'd recommend taking a look at this Ditra Installation Handbook before getting underway.

[userbob]

You kind of confirmed what I was thinking. I didn't think continuing through an inside edge would work well. I've read every installation guide I can find and this particular subject was never really covered to the degree where I was comfortable making a final decision.

How about that outside edge of the bench (where your knees are when sitting)? I think as long as I push the thinset down (working from top to bottom), that this should wok. The excess thinset can be pushed out the bottom of the sheet, which is at the bottom of the bench. Once I do my floor, I'll overlap the 2" that is necessary.

FYI, I do have the inside corners and outside corners that came with the Kerdi drain. I'm more referring to long edges though, not corners.

[Tool Guy - Kg]

For the outside corner where the horizontal seat meets the vertical face, go ahead and wrap it if you feel comfortable. But I'd suggest a couple things: Make sure to embed one plane before committing to the next plane so as to make sure it's lays flat. Second, I'd round the sharp outside corners so the membrane wraps tightly around it (it's hard to wrap sharp outside corners w/o getting an air bubble in there).

What substrate and thinset are you using? I edited my last post to include these questions at the same time you were posting, so I think you missed them.

[userbob]

The entire shower is built out of drywall with one wall being plaster (existing old wall I didn't demo). For thinset, I am planning on using Versabond, as that is much more readily available than unmodified thinset as suggested by Kerdi. I'm pretty comfortable with that as well as it seems to work just fine per the John Bridge book/forums.

Any suggestions on how to "round" the corner? Currently, the seat portion of the bench has a piece of drywall that sits on top of the front face piece of drywall. I thought this would add the most support. I'm afraid that if I try to round that piece of drywall that I may damage it, thus losing my firm support on that edge.

On another note, would it be a good idea to attach the piece to the seat portion, let that dry in place, and then go back the next day to affix the front face portion of the membrane?

Sorry for the 1,000 questions. I like to be 100% sure of each step prior to starting anything.

[Tool Guy - Kg]

Ask as many questions as you have until you're comfortable. That's what we're here for.

You can use a sharp utility knife to slice a 45 degree chamfer from the sharp edge. You don't need to cut much off...3/16" would be sufficient to aide in neatly wrapping the corner.

No, I wouldn't stop wrapping multiple sides of the seat if you're using one continuous piece. After the top is embedded, you will be able to tug on it to pull it tight around the corner to continue the process. While it would be easy to peel it up and away from the substrate, Kerdi will not slide around after it's been embedded in thinset.

[userbob]

Sounds like a plan. Thanks for the tips.

[userbob]

I am installing a kerdi pan in my new shower. The base of my shower is not perfectly square (around 57" x 52") and my drain is off-center due to the joists down below. The drain is very close to center from left-to-right, but it is closer to the curb of the shower than it is to the back wall.

I've never worked with a mortar base before and I didn't feel like attempting to learn the skill for a one-off job in my house, so I picked up the 6' x 6' kerdi pan and cut it down to size. This last weekend, I cut the pan to fit the space and everything visually looks correct. I'm running through in my head the potential problems I may encounter and I've drawing a blank. I've read in multiple places that if you have a situation where the drain is off center that the pan shouldn't be used, but I can't properly visualize why.

The pan is sloped towards the center, so even if one side is longer than the other, it should still slope towards the drain.
I can understand that the bottom row of tiles may not all be the same size, but isn't that always the case due to the slope?
Wouldn't you just make the space needed for the bottom row a little less than your tile height and then just cut each tile to fit the corresponding space? Your second row would all begin on a level line above the floor.

Is there something critical I'm missing here? I'd hate to attach my pan to the floor only to find out it can't be tiled correctly. Is this discouraged simply due to asthetics? I'm going to have large (12" x 24") tile with 1/16" grout lines, so it will essentially look like one big slab anyway.

[cx]

Zeke, it'll really help if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. We can give it a more generic title any time you like to suggest one.

The problem with your foam tray is that the perimeter is not at all level now that you've cut it to fit your shower floor. You can compensate for that by cutting your bottom row of tile, but you will hafta compensate for that by cutting the bottom row of tile.

With your large tiles that may not be a bit aesthetic problem, but it's gonna require substantial attention to detail.

My opinion; worth price charged.

[userbob]

Sorry about the splitting of topics. Every forum is different. Some want different topics in different threads and others (like this one) want them all in one.

I started to think about this some more, and I think only two tiles will have to be specially cut. These will be the two tiles on the left and right side where the diagonal of the slope doesn't meet the corner. The back row will all be one height and the front is on the curb which would need cut special anyway.

I got it in my head now. Thanks!

[Tool Guy - Kg]

Zeke,

As far as installing...
Are you planning on setting up a temporary ledger board to install the first "full" row of tiles? If you don't already know, it's NOT common to start on the very bottom row. Typically, you set up a perfectly level ledger board and start installing the first FULL row of tiles (which is the second row from the bottom 99% of the time) directly on it. It supports the tile so it doesn't sag down as the thinset dries. Then come back to remove the ledger board to cut and install the bottom row after the others have set firm to the wall.

[John Bridge]

Hi Zeke,


There's lots of talk about the perimeter leveling of the tray. I think the most important thing is getting the bottom of the tray level so that the slope is constant toward the drain. There is not a lot of slope on the Kerdi trays to be begin with, so it really important that they be set on a level surface.

[userbob]

Yep, I know all about setting the ledger board with the second row first. Been there, done that before. That is the main reason I thought it wasn't a big deal if the bottom row had to be tweaked slightly to account for the difference in height due to the non-centered drain.

John, I am in agreement with you. I would think by far the most important aspect is to get that pan put in level so the slope does what it's supposed to.

You guys rock btw. I can't believe how many responses I got in such a short time. Hopefully I"m not too lazy and I post some pics of this shower. It's my first kerdi shower (as you can probably imagine).

[userbob]

Well, I thought I was done with questions and now I have two more.

1. When I fit the pan into the space, I have about a 1/4" - 1/2" gap between the pan and the curb in one corner. Can I just fill that area in with thinset to the height of the pan, or do I have to go through the trouble of mixing up deck mud to fill in that gap?

2. Does it matter what color the thinset is beneath the membrane? I've noticed every picture I've seen is the gray thinset (which I'm assuming is the standard color for unmodified thinset), but, of course, I have white thinset as my tiles are white and I just bought the same stuff for under-the-membrane as for under-the-tiles.