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Can anyone help? Please....

Recently I gutted my 5x8 bathroom down to the studs and replaced the plywood floor with 3/4 inch plywood. I put in a Kohler Cast Iron Tub (K-716) 60" x 30-1/4" x 14". This is an Alcove install.

Here are my questions:

The space measures about 60 5/8", so I guess I have to fur out the walls. What should I use and how much do I fur out the wall? I ask this because the Tub Flange seems a little thick and I would imagine that when I overlap the 1/2 cement board that it might bend a little. Is this normal, or should the cement board be totally straight?

Also, I have heard that you should use a water resistant barrier behind the cement board and I have read anywhere from 4mil to 15 mil should be used. Also, one wall is an outside wall, do you use the same material?



Can you please let me know what type and size to use and how to adhere to the Tub Flange? I saw in a video that roofing cement can be applied to the Tub Flange and then you attach the bottom of the barrier to that....

Step by step instructions greatly appreciated and any suggestions and advice would be great!

Thanks,
Dave
 

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No vapor barrier in bathtub or shower enclosures. Refer to IRC R 702.4.3 for more information.

You can secure the flange with roofing nails either by driving the nails directly above the the flange and letting the head rest on the flange or by drilling holes in the flange and driving the nails through the holes. Make sure to follow the manufacture instructions when installing the tub.

The cement board should rest on top of the flange not lip over it.

Click on this link for more information:
www.schluter.com/index.aspx
 

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ARI001, correct me if I'm wrong, but I believe the code you refered to applies to greenboard not cement board. A moisture barrier is needed either behind the cement board or on top of it but not both. (creates a moisture sandwich) If you are furring out the walls so the flange is flush with the furring material, then you could use 6 mil plastic over the furring material and down over the flange. This way the cement board can be installed over the flange and remain flat. The width that you have can be gradually tapered with furring strips of less thickness the futher you get away from the tub. Or you can install the cement board above the flange, silicone between the flange and tub, then mesh tape and thinset the bottom edge so it remains flat. Thinset, tape the corners and butt joints. Before tiling Redgard the cement board.
Or the other option is fur it out,(forget the plastic) install the cement board over the flange and then Redgard. I have never used roofing cement anywhere in a bathroom. I believe your tub has a short thick flange, so over the top may work out best for you. Attach the tub as ARI001 suggested. When insulating use unfaced batts, or cut the paper of faced batts.
 
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