On Thu, Apr 21, 2011 at 1:44 PM, Sebastien Hubert sebastien.hubert@mc2000...> wrote:
Thus to summarize, in our building the earth plastering is done but we still need to do the last finish layer... At the moment we have more or less 5cm earth on the straw bale walls. Regarding the first house where they made the blower door test, on thebasement walls they only put 1.5cm earth plastering and the finish layer isnot done yet...
[BIG <snip> of extraneous, previously posted material]Here in North America where buildings are more often than not made "cheaply" as compared to the traditional "Old World" methods that are still used throughout much of the world, there is an approach in conventional building systems called the "Air-tight Drywall Approach" (ADA) which as the name implies, utilises the gypsum board interior sheathing ("drywall") as the major component of the air barrier strategy (along with acoustic sealants and gaskets at the joints between panels and at penetrations for services) rather than the more typical approach of utilising a separate membrane (usually a polyethylene sheet) which is typically called up as a "Continuous Air/Vapour Barrier" installed over the framing and cavity insulation before the interior gypsum board sheathing is installed.
A couple of these ADA details may be seen at: http://www.cmhc-schl.gc.ca/en/inpr/bude/himu/codemo/codemo_100.cfm http://www.cmhc-schl.gc.ca/en/inpr/bude/himu/codemo/codemo_098.cfm... the point being that it is not the thickness of a material that determines its effectiveness (drywall typically being a mere 12 mm thick) in an air barriers strategy but rather, it is how the various materials used in the air barrier strategy, are configured.
Wet-applied plaster is very effective as an air-barrier material simply because unlike sheet materials such a gypsum sheathing or wood panels, there are no joints between the individual panels that need to be sealed.
Control joint flashings (which should be used to break up the plaster into panels to eliminate the cracking that would occur as a result of temperature and shrinkage stresses or structural stresses like racking) are typically designed to ensure continuity so the weak points will typically be at the junctions between different planes (ie walls and ceilings, wall and floors) or different materials (ie wood and plaster) or at penetrations for services (ie electrical boxes, plumbing pipes, exhaust vents, chimneys).
These are best dealt with by the use of a flange underneath the plaster which overlaps the joint by 50mm or more on either side of the joint , preferably using an integral geometry to lock the materials together rather than having to rely upon acoustic sealants (they off-gas/stink and are messy) and/or compressible gaskets which will remain flexible throughout the lifetime of the building.
-- === * === Rob Tom Kanata, Ontario, Canada < A r c h i L o g i c at Y a h o o dot C A > (manually winnow the chaff from my edress if you hit REPLY)