Shower remodel questions [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-11-2010, 12:18 PM
I am about to remove an old 60" long fiberglass shower that goes wall to wall. I want to replace the shower with a porcelain tub, and then tile the walls and ceiling if the shower. I have a few questions:

1) I assume that I need to tear out the drywall that is above (and possibly behind) the existing shower unit, including the ceiling, and line the area that the new tub and tile will go into with cement backing board? I would not put drywall in behind the tile. Is this correct?

2) The tubs I looked at at Home Depot all have a 1" flange around the top edge of the tub. This flange needs to be screwed into the wall stubs, requiring me to drill through the iron flange, is this correct?

3) This flange on the iron tubs appears to be about 1/4" thick. Do I need to screw in a layer of 1/4" plywood on top of the cement backing board for the walls of the shower, to be able to tile over the flange?

Thank you in advance for any help you can provide.

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02-11-2010, 12:41 PM
I want to replace the shower with a porcelain tub

Are you talking about an enamels cast iron tub?

1) If you wanted to you could use kerdi to go over the drywall, as long as the drywall is in good shape. Otherwise yes, you would tear it out and install CBU

2) Most people use roofing nails, which have a large flat head, and nail in right on top of the flange, not through it. I do the same but with pan head screws. You cannot drill through cast iron. If it was plastic you could drill trough it.

3) What I do is but the CBU to the top of the flange, then fill in the gap with mortar, using mesh tape to bond it to the cbu. Then I would use a liquid membrane, like hydroban or redguard to waterproof the cbu.

If you are framing out the tub area it is best to make the opening a bit smaller, then notch out for the flange so the backerboard just comes over the flange.

Houston Remodeler
02-11-2010, 12:58 PM

We can give you better advice if we knew what waterproofing method you are planning to use. Poly behind CBU ? Surface applied liquid ? Surface applied sheet membrane (kerdi)?

02-11-2010, 01:16 PM
Gregg, Yes, I am talking about a porcelain enamel tub.

Paul, oh boy, am I showing my ignorance here. I had assumed that tile with thin set over CBU would be waterproof. It seems like you just saved me from making a major mistake. What should I do to waterproof it?

Thanks again


Houston Remodeler
02-11-2010, 01:43 PM

No, tile over CBU is not waterproof. Glad we caught that one early. Spend some time in our world famous Library, linked in the blue bar above, to the left, under FAQ. Word search under kerdi, hydroban, redgard (or redguard), and poly behind CBU. I vote for Kerdi all the way. :tup2: