Do I need a vapor barrier on tub surround with 1 external wall?

Question

I know variations of this question have been asked dozens times and it seems like there is no real consensus. Each post or website I look at seems to advocate something different. I understand that some of this is because of different scenarios in regards to the build, products, locations, etc.

I'm getting ready to re-tile a small bathroom and here are the particulars:

It has a common bathtub and I'm planning on re-tiling just the bathtub surround. 1 of those walls is an external wall (with a window). The remainder of the bathroom I plan on painting.

• The tile will be glazed ceramic/porcelain.
• I will probably use hardie-backer as the cement backerboard (Lowes is the closest big box store, so I'll be making my common supply runs there and they stock this and the reviews are all pretty solid on it.)
• Location is central Indiana (Indianapolis)

I have not begun the demolition yet, so I'm not positive on what the insulation situation is on that external wall. I know some types of insulation have a vapor barrier on one side, and I know that can/should impact the decision here. I may also replace the insulation if need be, to ensure a good quality job here (also in case of any water damage or mold found obviously).

So, do I need to put a vapor barrier on all 3 sides of the tub surround in this scenario? If the insulation already has one, should I only put a vapor barrier on the other 2 walls of the surround (the non external ones)? If I put my own insulation in, should I opt for some without a vapor barrier side and just add a full vapor barrier to all 3 sides instead?

Answer 1

You need more than a vapor barrier...you need waterproofing. Tile and grout and hardi-backer aren't in and of themselves waterproof.

The easiest way to do this is to use Redgard. You put up the backer board, tape and mud the seams, then you paint the Redgard on. This creates a completely waterproof rubberized waterproofing layer behind your mortar/grout and tile.

Answer 2

Pertaining to External wall:

No if, there's no insulation currently or if you don't find any mold nor wetness in the existing insulation. Leaving well enough alone will keep doing what it does.

Yes if, you really do a full depth tight insulation & just go with tar paper faced batts. Triple quadruple layers of this & that just add problems when the rest of the house isn't getting redone equally.

Internal Walls would only need the tar paper faced batts as well, IF you'll be insulating for sound. IF NOT, then don't change anything & let the house do what it's always done there too.

Answer 3

Greenboard>15lb roofing felt>1/4" hardibacker. Use admix in your mortar and add 1 part to grout mix as well. Seal all grout lines 36 hours after install. Finish with clear silicone caulk for wet areas.

I've never had a shower surround fail.