Will this installation create a vapor barrier?

[Judson Bryant]

Location:Houston, Texas; Summer climate-95 degrees 70-75% humidity outside; interior 72 degrees, 50-55% humidity.
Small bathroom with 5'0" tub-shower combination butting up to exterior wall.
Wall construction from exterior to interior: primer, 2 coats exterior latex paint; LP 7/16" x 8" lap Smart siding; #30 felt; 1/2" CDX; 3-1/2" unfaced R-13 fiberglass; #15 felt;7/16" cement backer board; thinset mortar; 4-1/4 x 4-1/4 semi-glosss ceramic tile. As I understand it, the LP Smart siding has a perm rating slightly in excess of 1. Will the ceramic tile installation create a vapor barrier or will moisture vapor diffuse through the grout joints every 4-1/4"?

[dgbldr]

Theoretically no. Practically, almost. 4-1/4" tile has self-spacers and is usually installed with very thin grout lines, so yes vapor will get through it but very slowly. With all those layers of felt, paint, etc. you won't get much vapor all the way through the assembly.

What's the concern?

[AndyGump]

Location:Houston, Texas; Summer climate-95 degrees 70-75% humidity outside; interior 72 degrees, 50-55% humidity.
Small bathroom with 5'0" tub-shower combination butting up to exterior wall.
Wall construction from exterior to interior: primer, 2 coats exterior latex paint; LP 7/16" x 8" lap Smart siding; #30 felt; 1/2" CDX; 3-1/2" unfaced R-13 fiberglass; #15 felt;7/16" cement backer board; thinset mortar; 4-1/4 x 4-1/4 semi-glosss ceramic tile. As I understand it, the LP Smart siding has a perm rating slightly in excess of 1. Will the ceramic tile installation create a vapor barrier or will moisture vapor diffuse through the grout joints every 4-1/4"?

First, I hope that the primer is not the outermost layer.

I am a big proponent of allowing walls to dry to both the interior and the exterior.
I like the idea of the 15# builder's paper on the interior behind the cement board. I think I would go with Tyvek or some such over the sheathing as a drainage plain then use 3/8" thick furring, then the lap siding.

Just my opinion.

Andy.

[Mark Parlee]

Judson
Over the cement backed board we apply a liquid water proofer so it had better not dry to the inside.
http://www.laticrete.com/contractors...rproofing.aspx

[Judson Bryant]

My concern in asking this question is prompted by my experience with vinyl wallpaper applied to an exterior wall in Houston's air-conditioning climate. I well remember my first experience stripping such wallpaper off of a wall and finding a mixture on water condensate and mold on the back of the wallpapr and on the front of the drywall-a first class mess.The wallpaper was a vapor barrier. I do not want such a situation to develop in the backer board or tile. Also, I don't want to over analyze the installation.
Andy, you are correct. The primer is not on the exterior. I have been known to transpose things on occasions.
Mark, I considered applying HydroBan. The tech representative at Laticrete indicated that the recommended thickness has a perm rating just in excess of 1.00. I do not have enough theoritical experience to determine if the interior assembly of #15 felt, 7/16" backer board, HydroBan, thinset mortar and glazed ceramic tile wiil act as a vapor barrier. Does placing two materials,each of which have 1.5 perm ratings, together produce an assembly with a perm rating of 1 or less?
Thank all for comments.

[ThingOfBeauty]

The glazing on the ceramic tile is a vapor barrier, but the rest of the layers on the inside of your proposed wall should manage the water just fine.
Your layers are pretty much how we do it, we use felt (lapped to drain into the tub or shower receptor) on exterior walls so diffusion from outdoors has a place to go--down the durock between the felt and the waterproofing or tile.

A tile assembly will be much more permeable than vinyl wallpaper, not to mention it doesn't cover as much of the wall. You're unlikely to have a problem even without the felt etc., at least around here you would not...houston is a lot more humid though so I'm kind of guessing about down there.