Ask tile installer to use Laticrete 9235 (or similar) brush on  

membrane over hardibacker to create continuous waterproofing under  

tile.  After using a number of techniques, this seems to be the best  

way to protect against water infiltration if a leak presents itself.   

Make sure to spray foam all penetrations (knobs, shower head, etc.)  

before applying the membrane.

Erik Heikel



On Dec 18, 2008, at 7:27 PM, Tim Yandow wrote:



>> I am interested to know if anyone has an opinion about or  

>> experience with

> the following situation:

> I am currently constructing a 2000 sq ft double wall, dense pack  

> cellulose

> house. Due to a number of factors, an upstairs shower stall, 4' X  

> 4' ended

> up in an outside corner of the house (north west corner). I know  

> this is

> not a great spot for it, but there it is. The tiler would like me  

> to place

> a vapor barrier over the framing before the hardy backer and tile  

> go on.

> There is 12 inches of cellulose in the walls with a thermal break  

> (2- 2x4

> walls) behind the shower. This I presume is to keep moisture from the

> shower away from the insulation. I am wondering if this is a good idea

> given the porous nature of tile and hardy backer. Any input? Thanks.

> Tim Yandow

>

>

>

> I am not sure what makes the most sense here

>>

>> --- On Tue, 12/16/08, William C Badger AIA

>> <[log in to unmask]> wrote:

>>

>>

>> Stain may be fine for certain applications, but white stain does  

>> not cut

>> it on a 19th Century Greek Revival building. There are many  

>> applications

>> where paint is the only suitable coating and our wall sandwich has to

>> accept that.

>>

>> Acrylic water-based primers and paints are relatively vapor  

>> permeable, as

>> long as they don't have lead or zinc oxide pigments.

>>

>> I have been on the scaffolding and seen soggy paper mache that was  

>> once

>> cellulose insulation pulled out of walls.

>>

>> Without the forensic analysis that would determine the source of the

>> moisture, that anecdote indicates nothing.

>>

>> Try telling the owners of a late 18th Century library that all the  

>> books

>> and shelves need to be removed and the wood paneled walls painted  

>> with

>> vapor barrier paint. For that matter, any old house with an  

>> historic or

>> just well finished interior is not a candidate for an interior vapor

>> barrier.

>>

>> Many of the early cellulose retrofits had insufficient density to  

>> prevent

>> the air movement that is the primary vector of moisture in walls. If

>> properly dense-packed, and interior humidity levels are appropriately

>> controlled (and there are no sources of bulk moisture, such as wet

>> basements or crawl spaces or ice dam leakage), cellulose retrofits  

>> do not

>> require a vapor retarder. In fact, one cellulose manufacturer -  

>> Applegate

>> - will void their warrantee if a vapor retarder IS used.

>>

>> More attention is being paid to the "flow-through" concept of  

>> moisture

>> control, allowing drying in both directions.

>>

>>

>> In 1979 a field study in Portland, Oregon (4,792 degree days)  

>> concluded

>> there is no risk of moisture damage in mild climates without a vapor

>> barrier

>>

>> A second major field study was done in Spokane, Washington (6,835  

>> degree

>> days) by George Tsongas, Ph.D. P.E. Professor of Mechanical  

>> Engineering at

>> Portland State University. The exterior walls of 103 homes were  

>> opened, 79

>> with retrofitted insulation and 24 uninsulated as a control group.  

>> “This

>> study strongly concludes that the addition of wall insulation  

>> without a

>> vapor barrier does not cause moisture problems in existing homes in

>> climates similar to that of Spokane.” Bonneville Power Administration

>> provided funding for this study.

>>

>> A 2004 study released by building scientist Erkki Kokko of Finland,

>> ”Hygroscopic Cellulose Fiber Insulated Structures” found the use of

>> permeable building materials resulted in improved indoor air  

>> quality. The

>> absence of a vapor barrier, such as polyethylene film, allowed the  

>> wall to

>> absorb and desorb relative humidity. This enables the interior  

>> relative

>> humidity to remain more constant and comfortable to the occupants.

>> They also found a 30% reduction in the carbon dioxide levels.

>>

>> The EEBA’s Builder’s Guide for Cold Climates states in Appendix III,

>> “Polyethylene on the inside of building assemblies in cold, mixed- 

>> humid,

>> mixed-dry, hot-humid, and hot-dry climates is not generally a good

>> idea.” “A classic flow-through wall assembly should have a permeable

>> interior surface and finish and permeable exterior sheathing and  

>> permeable

>> building paper drainage plane.” This permits drying to both the  

>> interior

>> and exterior.

>>

>> In a December 2001 presentation in Proceedings of Thermal  

>> Performance of

>> Building Envelopes VIII, Asst. Prof. John Straube stated “In many

>> practical situations, a low permeance vapour barrier will not improve

>> hygrothermal performance, and may in fact increase the likelihood of

>> damaging condensation or trap moisture in the system. In some  

>> cases, a

>> low-permeance vapour barrier may be called for, but in many practical

>> high performance enclosures, none is needed, and eliminating them  

>> will

>> actually improve performance by encouraging drying and avoiding

>> solar-driven diffusion wetting.

>>

>> I would pose a typical problem building for group comments. A late  

>> 19th

>> Century structure with some timber frame and some stick built  

>> walls. The

>> bulk of the walls are uninsulated with clapboards nailed directly  

>> to the

>> studs (no sheathing). The interior walls are lath and plaster with  

>> 1/2"

>> Celetex over it and 1/4" plywood paneling over that. It has a stone

>> foundation and slate roof. The attic is vented and the attic floor is

>> insulated with a nominal 12" of fiberglass, but electricians over the

>> years have done their best to rearrange it. The paint tends to  

>> hold fairly

>> well, but is a mix of relatively new coatings and what ancient  

>> bits have

>> still hung on. Will dense pack cellulose exert enough pressure to pop

>> clapboards off (small cut nails are what was used)? Will moisture  

>> transfer

>> peal the paint?

>>

>> As long as moisture sources are mitigated (stone basement?) and  

>> interior

>> humidity levels are controlled with appropriate ventilation, this  

>> might be

>> a good candidate for dense-pack cellulose. It's unlikely that the

>> installation would pop the cladding nails, as aged wood has amazing

>> holding power, unless previous rusting has deteriorated the bond.

>>

>> Ironically the potential problem in this case might be the  

>> presence of an

>> interior vapor barrier - the Celotex, with its double foil  

>> facings.  Since

>> the exterior cladding has no weather-resistant barrier (not even

>> sheathing), there is a potential for wind-driven moisture  

>> penetration,

>> particularly if there is a high exposure level (no trees or other  

>> adjacent

>> buildings as protection).

>>

>> This wall structure would have to do all its drying to the  

>> outside; but

>> since there should be little moisture drive from the inside, the  

>> outward

>> drying force may not be sufficient to lift the paint.

>>

>> But, if I were interested in preserving this building, I would  

>> consider

>> removing (and either saving or replacing) the exterior cladding and

>> installing a weather-resistant barrier (probably 15# felt or grade D

>> building paper). Without such a secondary drainage plane, it's  

>> likely that

>> you would be up on that scaffolding again removing soggy cellulose  

>> and

>> rotted wood.

>>

>> Removing the cladding would also allow the cellulose to be blown  

>> in behind

>> InsulWeb netting for a more complete installation (around knee  

>> braces,

>> etc), then covered with WRB and siding.