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-   -   Tub Surround Installation Question (https://www.johnbridge.com/vbulletin/showthread.php?t=112454)

zaphod 04-25-2014 08:29 AM

just to make sure, the one labelled floor tile mortar is the right one?


Yep, I know where that is, I'm building my own house (literally) on 5 acres in an agricultural zoned area near sunshine grove road. I'm right next to the expressway, in fact it cuts off 0.1 acres of my property. I have a yahoo group about it here:


Richard Tunison 04-25-2014 09:06 AM

Yes, that is the right product.

zaphod 05-01-2014 06:10 AM

A quick question about installing kerdi membrane on my fiberglass tub surround. 11) What do I do where the kerdi overhangs the tub lip? Do I just make the thinset go over top of the lip.. not sure how that would stick to the fiberglass... or should I just put the thinset on the perma base then perhaps silicone the kerdi to the tub lip later? any suggestions?

Richard Tunison 05-01-2014 06:18 AM

Yep, adhere it to the flange. I'd use this product instead of silicone.

PC7060 05-01-2014 06:36 AM

The link Richard provided is the self leveling crack sealant version of Sikaflex, good product but kind of runny for use with Kerdi.

I use this version of the product for tile work.


This post on my thread shows kerdi band and corners installed with Sikaflex.

Richard Tunison 05-01-2014 06:45 AM

Thank you P.C.!!:yo:

PC7060 05-01-2014 08:17 AM

No problem, Richard, glad to help. :)
I'm not so helpful with questions on thinset, if the answer isn't versabond I'm sunk. ;)

zaphod 05-02-2014 05:16 AM

Thanks for the info and link.
a few questions:

12) how should I apply this? Should I attach the kerdi to the permabase with the thinset first, then come back and try to get the sikaflex between the kerdi and the tub lip... or should I attempt to do both at the same time?

It looks like you only use this on corners that don't overlap at least 2" I have a few 36 degree corners, one inside, one outside, I can't think of any way to deal with that angle other than to just cut the kerdi to the corner and overlap it... the overlap will end up being zero right at the corner and increasing the further it gets from the corner. It seems like using sikaflex on these odd corners would be a good idea.

13) is the procedure for attaching kerdi with sikaflex the same as using thinset? Do I use the same size V notch trowel.. etc?

PC7060 05-02-2014 06:02 AM

12 - I'd put the thinset on the cbu using 1/4" notch and then spread the Sikaflex on the tub flange with a 1" flexible putty knife. Then apply the kerdi band using a 6" blade or the flat side of your trowel to even out the thinset under the kerdi (no tiger stripes).

Use the putty knife to make sure the kerdi band is fully embedded in the sealant and you are done.

13 - see above for tools and methods.
Re the 36 degree corners, are these on the tub surround too? Probably OK there where the tub flange helps control the water. I'd be concerned if you doing that in the water proof area of a shower or bench where any leakage is unacceptable.

Got any picture of the problem area?

zaphod 05-02-2014 07:44 AM

3 Attachment(s)
Here are pictures. my house has 10 equal sides arranged in a huge decagon, making each of the corners 36 degrees. This little shelf is just something to fill in the corner with, it will have cabinet doors under it, mainly so I can get in there if I ever need to access the pump. This is a Jacuzzi tub that is set up to be a bathtub ONLY, there is no shower head, just the spout to fill the tub... there is a corner shower only in the same bathroom just on the other side, so we didn't need 2 showers in there, and this way we don't need to have any kind of shower curtain or wall on the end of the bathtub... it's just going to be open. The outside 36 degree corner, I'm really not too concerned with because if any thing ever did get behind there, it's open on the bottom and it could dry out, and it's above the bathroom floor which wouldn't hurt if it ever got wet... and chances are if there was water by that particular corner, the floor would be wet anyway. It's the inside corner that I'm mainly thinking about... however, not overly concerned because it's not in a shower area, and it won't be getting soaked on purpose ever. I did put a slight pitch on this shelf toward the tub, so hopefully any water on it would run into the tub anyway.

I would still like to do the best job I can waterproofing this, so I'd appreciate any input on how to handle these 2 non-90 degree corners. I'm trying to think of the best way to do it without causing too much buildup that might be a problem later.

PC7060 05-02-2014 05:10 PM

I think I'd use something like Redgard or Aquaban to seal the joints and the odd sized corners similar to Jr's example in the link below.


zaphod 05-06-2014 12:36 PM

Thanks, that looks like the way to go with those odd corners.

I got some Sikaflex as recommended in the link provided, and I'm getting ready to try to install my kerdi membrane over the tub lip, but now this brings up another question:

14) how far down do I bring the kerdi? there is about a 3/8" radius between the vertical and horizontal part of the tub edge, but part of that will be behind the kerdi because my premabase sticks out a little past it. Do I bring it down all the way to the horizontal part, or do I bring it most of the way down, and perhaps leave a gap under it?

15) while I'm asking.. how far down should the tiles go? I think it might be asking for trouble to attempt to bring them all the way down to where it is horizontal, because the fiberglass tub may not be perfectly flat.

Richard Tunison 05-06-2014 12:52 PM

Bring the kerdi down so you can comfortably get it glued to the vertical flange,,,,,,no need to get down to horizontal.

If the tub is not level you will want to make the layout so that you are cutting the bottom row of tiles to conform to the tub.
Leave an eighth in. gap for 100% silicone caulk.

zaphod 05-06-2014 01:41 PM

ok, thanks! I put a level on the tub and it is nice and level, and mostly flat, looks like a total variation of less than 1/16" it's hard to measure.

16) should I make the gap under the tiles a minimum of 1/8" so where the tub dips down slightly I'll have a little thicker gap? The thickest part would be less than 3/16"

I also have a few places where I need to build up something on top of the permabase... there is one edge where the drywall is about 1/32 thicker than the permabase, so my bullnose tiles would have a problem, and another where the corner of my shelf is about 1/8" short of where the corner should be.

17) should I fix these areas with something like a layer of thinset before I install the kerdi, while I'm installing it, or after I install it? I'm thinking I might want to do it either before or after because it looks like I want the thinset pretty thin to install the kerdi and need to be working fast, not fooling with corners.

Richard Tunison 05-06-2014 01:55 PM

16. Pushing 3/16in. is,,,,,,,,,,,in my opinion, just to big and unsightly. I like a small 1/8 but that's just me. If you like it,,,,,,,,,,I like it. :biker:

17. I'd do the minor repairs with thin set before the kerdi and of course let them dry.

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