basement bathroom substrate and vapor barrier?

Old 08-09-13, 08:56 PM
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Join Date: Aug 2013
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basement bathroom substrate and vapor barrier?


First off, this is asking a bit about paint and tile and walls but it is all bathroom specific so i still thought this would be the best place for it. if not, please let me know and I will move it to wherever you would recommend.

I am working on finishing my basement and I was hoping to get some advice concerning a bathroom that I am putting in and the substrate to use.

First of all, my situation:

The bathroom is about 100 sq. ft. it is all below grade in the basement. All the framing is 2x4 16 in. o.c. 3 walls are on the interior of the building and one is the outer concrete wall. I have closed cell spray foam insulation on the exterior wall between the studs. The floor is concrete. I have a bathtub inside the bathroom with 2 walls on the sides of the tub that are interior walls and one wall along the exterior wall and the last side open to the rest of the bathroom. I have a Panasonic 40 cfm ERV for ventilation and I have cellulose insulation in between the ceiling joists (again 16 in. o.c.) that is held up by thick clear plastic. I am in the dry, Colorado zone 5 climate. I am planning on having tile around the tub on the walls all the way up to and including the ceiling, having tiles on the floor and up to waist level on the walls, and then painting the walls and ceiling elsewhere.

My question:

How/what do I do for drywall/backer board/substrate? How about a vapor barrier?

I cannot seem to find a clear answer on this at all. I know that I should use cement board for the shower surround but that is about it. For the ceiling (in the tub area ceiling = tile, elsewhere = paint) and other walls (tile half way then paint) I am not sure what to use. I have heard not to use greenboard at all. Some people say to use regular sheetrock and paint and the paint will be a moisture barrier. Some swear by densarmor or fiberock. Some still say they use greenboard (or blue or purple, all the MR gypsum board is about the same right?) I have heard that I should never have a plastic vapor barrier in a basement. I have also heard that I should not have a double vapor barrier as it would trap moisture and create mold in between. However, I have heard that I should always have a plastic vapor barrier behind the cement board, covering thinset, and tile because that is all porous and water will go through. I have heard that using paint can prevent moisture getting through but then wouldn’t I run in to a double vapor barrier situation if my walls along the outside concrete wall that has been covered with sprayfoam are painted? Sprayfoam is a vapor barrier too right? Should I put up plastic behind the concrete backer board on the two interior walls around the tub but not the exterior spray foam covered wall? What about the studs there, they will get wet through the concrete and tile right? Do I need to remove all the cellulose and plastic sheets holding it up in the ceiling joists because I plan on painting the ceiling and that would create a double vapor barrier?

So with all that, I guess what my main questions are:

1) Where should I put a plastic vapor barrier behind the substrate (if anywhere)?
2) Where do I need to remove existing vapor barriers such as the plastic sheet holding the cellulose insulation in the ceiling (again, if anywhere)?
3) What material should I use for the various walls and ceilings to avoid double vapor barriers, water destroying things, mold, sagging, etc.?

Sorry, I know this is quite a long post but I was trying to cover everything. Thanks for any ideas or help!

Old 08-10-13, 11:27 AM
Join Date: Nov 2012
Location: USA
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Hey I am by far no pro. But I just did my basement bathroom and installed a new shower. I used plastic/vinyl vapor barrier behind the bb (I used durock) this drops down into the pan so any water that may get behind the tile will find its way to the pan and the drain. I have also read on here the best way to seal it is to paint this stuff over the bb but its expensive and after speaking will some contractors over kill. As for the rest of the bathroom it's all Sheetrock and tile I'm pretty sure unless its a wet area you only need Sheetrock. Hope this helped a little

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