Help needed for 5 x 8 Bathroom Remodel

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4hunters

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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. 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
 

Jadnashua

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Depending on how high the tub flange is, you dont' need to bring the cbu down over it...you can bring it just down to it. It's only an issue if you are using small tile - you want more than 1/2 of the tile supported by the cbu (as opposed to on a floor where you want at least 90% fully supported, and preferably 100%).

You can use plastic or roofing felt behind the cbu. If there's insulation with a vapor barrier in the wall, slash it some so you don't have a vapor 'sandwich'. You dont' need to anchor it to the flange. Lap it over, put up the cbu, and you can trim it before you put the tile up. You should caulk that joint (i.e., the tile should NOT touch the tub surface). For tile help, check out www.johnbridge.com.

If you'd like to eliminate the caulk, you could do as I did and use Dilex from www.schluter.com at the tub/wall inteface. I didn't use a similar expanion joint on the wall junctions because they were not very plumb, but that's not a bad idea, either.
 

4hunters

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Anybody else out there have any suggestions? It seems that there are a lot of different ways to waterproof the alcove as well as installation of cbu. Thank you in advance.
 

Jadnashua

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First off, cbu isn't waterproof. It is not affected by being wet, though, which is one reason why it is used. Stick it in water, and it will absorb the water, maybe wicking up as much as 6" or so. The other major reason it is used is that it expands and contracts the same as tile, so they don't try to pop off.

The vapor barrier behind it is to prevent moisture from condensing and rotting the wood. A properly done shower area shouldn't have standing water so no extensive wicking, and if you can keep the wood behind from getting damp, will be fine. The tiling flange is critical as is getting the tub perfectly level which can cause pooling or intrusion into the walls.

You can use a surface waterproofing like RedGard, or a membrane like Kerdi if you want it waterproof.
 

GabeS

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The CBU can go up to the top of the tub flange as Jim suggested.

Another option, which is more work for you, but my preferred method, is to shim out the wall flush to the tub flange or a little more outward than the flange. Then when you install the CBU, put shims on the tub and rest the CBU on the shims keeping the board about a quarter inch off the tub deck before screwing it in. This will prevent the CBU from wicking water.

To shim out the wall you can you regular 3/4 inch wood if that's enough or rip 2x4's on a table saw to the proper depth. Or if the existing studs are not level, you can sister new 2x4's on the old and level as you go.

As Jim stated, the CBU is not "waterproof". It is not necessary to waterproof the wall however. Put clear plastic over the studs and then put on the CBU.

When cutting the CBU, use a CBU knife and score the line numerous times (I do at least 8) to get a clean break.

Gabe
 

Erico

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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. 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

You might find a surface applied water proofing barrier will make your tiling easier. The cement board soaks up a lot of water and dries out your thinset. Applying a surface barrier will waterproof your shower AND help the thinset cure slower allowing for more "working time."
 

4hunters

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Thanks Gabe!

I like the way you think. I was toying with some ideas in my head and what you suggested was one of them. I would think that this would ensure that in the event something went wrong with the caulking or something else that the water would not get behind the tub. Also, should I put the plastic on the outside wall? I read that this would cause condensation or something.

One more thing, the tub is almost completely level on this own, should I make it perfect?

Have you used this method yourself?

Thanks again Gabe.

-Dave


The CBU can go up to the top of the tub flange as Jim suggested.

Another option, which is more work for you, but my preferred method, is to shim out the wall flush to the tub flange or a little more outward than the flange. Then when you install the CBU, put shims on the tub and rest the CBU on the shims keeping the board about a quarter inch off the tub deck before screwing it in. This will prevent the CBU from wicking water.

To shim out the wall you can you regular 3/4 inch wood if that's enough or rip 2x4's on a table saw to the proper depth. Or if the existing studs are not level, you can sister new 2x4's on the old and level as you go.

As Jim stated, the CBU is not "waterproof". It is not necessary to waterproof the wall however. Put clear plastic over the studs and then put on the CBU.

When cutting the CBU, use a CBU knife and score the line numerous times (I do at least 8) to get a clean break.

Gabe
 

GabeS

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No problem.

The clear plastic vapor barrier gets directly stapled to the studs before the CBU. Leave it long and let it hang over the tub. Then install the CBU and cut the excess plastic with a razor as Jim suggested.

Yes, you should install the plastic on the exterior walls also. Also make sure there is insulation on that wall also. Try to avoid putting the plumbing on the exterior walls if that's an option.

As Jim suggested be careful no to place two vapor barriers on the wall and create a sandwich which could trap moisture. Either you put the plastic on the studs and then CBU or you apply a surface waterproofing membrane but not both. If there is already foil faced insulation in wall then put a ton of slashes in it to allow moisture to escape. The point is to stop the bathroom moisture from getting in the wall, but also allowing any little moisture that does get in an escape path to the outside. The tyvek or building paper on the outside is breathable and allows the moisture to escape.

If the tub is not already installed, do everything in your humanly power to make it 100% level. A cast iron tub is going to be difficult to manage so have a lot of help. A cast iron tub doesn't necessarily need a mortar bed underneath. Good luck.
 
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