[GSBN] [nbne] Earth plaster and Cellulose

[Ian Redfern]

Good morning Jacob,

Thanks for the invitation to comment from this outreach of the straw bale
building network.
    Here in northern New Zealand with a climate not too unlike the lower new
England states and certainly similar to Oregon and coastal Washington State
where we have sub cyclonic conditions with continuous high humidity (80 ­
100%).

    Over more than 15 years of designing natural (adobe and straw bale)
houses and observing the lime plaster putty based plasters, renders and
white washes on them ­ the lime putty based products have stood up
fantastically to wind driven rain and shedding internal humidity on straw
bale and earthen walling !

    Lime putty based white wash (simple lime putty and water   AND not thick
creamy stuff) is fantastic at healing any micro cracking that may occur
during the seasonal changes ­ we specify an initial five coat on the green
render coat then annually (I have just redone [render in parts and three
coats of whitewash] on the exposed sections of our adobe cottage after 6 or
7 years)

    As said in an earlier thread the rogue element is in installing any form
of vapor barrier in the wall matrix ­ the vapor needs to be pulled to the
outside and lifted off by the infinite atmosphere (we express this as the
drying effect of air movement around the building (outside air movement
reduces the water vapor [and other gasses] partial pressure at the wall
surface  which is why we purposefully leave a rough textured surface)

   I trust this is not too detailed ­ it is better expanded on by Straube
and Burnett in their book "Building Science for Building Enclosures"

Cheers

Ian

    The timber framed houses we have designed and built use a polyester
insulation between the framing with a vapor permeable building wrap then
cavity battens (20mm =  3/4") behind the lime plaster that is reinforced
with a polypropylene expanded mesh, then the 5 coats of whitewash   =
reassurance to client, building regulator, and contractor
And still doing well after many years of coastal battering (this home has
generous eaves on the second story but the lower level receives full force
of wind driven rain)

 
  www.adobesouth.co.nz   Ian Redfern
 Adobe South
 A:    5 Lancewood Rise, Onerahi, Whangarei
 P:     09 436 4040      M: 027 490 2324
 E:     ian at adobesouth.co.nz

From:  Jacob Racusin <buildnatural at googlemail.com>
Reply-To:  Global Straw Building Network <GSBN at sustainablesources.com>
Date:  Sat, 27 Apr 2013 10:22:50 -0400
To:  Derek Stearns Roff <derek at unm.edu>, "<nbne at lists.riseup.net>"
<nbne at lists.riseup.net>
Cc:  "<gsbn at sustainablesources.com>" <gsbn at sustainablesources.com>
Subject:  Re: [GSBN] [nbne] Earth plaster and Cellulose

Great reference Derek. The inclusion of multiple coats of limewash does a
lot to limit bulk water absorption in the plaster, reducing the "charge" of
the reservoir cladding.

Having met with the architect, I learned their chief concern is not vapor
drive, but wind-driven moisture through inevitable cracks in the plaster
bulk-loading water into the assembly. They cited hurricane exposure as an
extreme design condition, and the issue was less about the cellulose and
more about the location of the structural framing (as opposed to a
bale-wrapped timber frame). Certainly good arguments for wood cladding, lord
knows the storms are only getting stronger and more frequent...

Thanks to those who replied!

Jacob

Sent from my Windows Phone

From: Derek Stearns Roff
Sent: 4/26/2013 5:55 PM
To: <nbne at lists.riseup.net>; Jacob Deva Racusin
Cc: <gsbn at sustainablesources.com>
Subject: Re: [nbne] Earth plaster and Cellulose

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