kerdi for a tub surround? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-30-2009, 05:34 PM
Ok, I'm making plans, now that my bathroom is gutted. (This is the 140-year-old house I was asking about flooring on.) I got John's Kerdi book, and it's pretty cool stuff; I'm thinking I'll use the Kerdi membrane for the tub surround. The tub is a really old cast iron tub that's in perfect shape (I wish it was white, not pale peach, but you can't have everything, and I'm not buying a new one!). My question is the flange--it's only about 1/2" high! Modern flanges are bigger, aren't they? Is the Kerdi going to work ok? Do I put the sheetrock to 1/4" over the tub like I would cancrete backerboard if I were doing another method?


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08-30-2009, 05:47 PM
Oh, wait--another question. It's a small bathroom (6x8) and the tub is along the back (8 foot) wall with the drain end on the right-hand wall. The sink goes to the left of the tub and there is 31" of space on the floor there. What I really want to do is build a vanity there and tile the tub side, so there's a knee wall to cut down on splashing from enthusiastic children. Can I do that when there is no flange on that end? Thanks!

08-30-2009, 05:57 PM
Debbie, you can bond the lower bit of Kerd to the tub flange with Kerdi-fix. Your drywall can stop about 1/8" from the top of the flange, then let the kerdi overlap the flange. Trim it so it will be covered by the tile. The end where there is no flange is a bit of a problem. You could bond the Kerdi to the outside edge, but you'd have trouble reaching it and it would be a trough that collects water. Hopefully, one of the pros will stop by and give you better advice.

09-02-2009, 01:39 PM
If I decided to do Redgard instead, would that work with the little flange as well? I'm having a hard time finding Redgard information--anybody have a good link? Pricing the Kerdi, I'm thinking that since this is going to be the backup shower (read: not used so much), I don't want to spend THAT much, and since it's just the tub surround, not the whole floor, pan, etc. thing, water sitting in the bottom isn't an issue. Specifically, does anyone have a good suggestion for me on how to build onto the side of the vanity so it's an effective third side for the shower, and so that water can't get between the tub and the vanity?


09-02-2009, 01:49 PM
Debbie, there are such things as flange kits that some manufacturers use to convert a drop-in tub to an alcove tub. These are vinyl moldings with a peel-n-stick side that glues to the edge of the tub. The shape makes a flange that would be your third line of defence (first two being the caulk at the backerboard to tub joint, and the second being the caulk between the tile and tub).

Here's a link to Redgard. (

Using Redgard, you have a choice for waterproofing the tub to backerboard joint: 1) (ideal) use their fiberglass mesh to form a bridge over the joint, then apply the membrane in at least 2 healthy coats over the mesh and the entire surround. 2) Coat the backerboard with Redgard, then caulk the backerboard to tub joint with 100% silicone caulk. This requires the backerboard overlap the flange, so some wall shimming may be required.

09-03-2009, 08:34 AM
Flange kits. I'm searching and searching the internet and finding nothing that isn't specific to a certain tub. Wouldn't you think you could get some kind of flange-by-the-foot? I only need two feet...anybody have any links for me? I live in the middle of nowhere--it's an hour even to Lowes and Home Depot, so I'm a big internet buyer.

09-03-2009, 08:38 AM
Sorry, Debbie, but all I know about are the ones you probably found. They'll work for you, but you end up buying far more than you need.