[GSBN] Looking for experiences with AAC and Rastra

Thu Dec 23 19:18:51 UTC 2010

Bruce, you sound so equivocal about this.  Can't you be more definite?
John

On Thu, Dec 23, 2010 at 9:42 AM, Bruce King <ecobruce at sbcglobal.net> wrote:

>
> We couldn't stop Rastra from leaking ABOVE grade.  It, and AAC, is highly
> porous.  Don't even think about using it below grade.
>
>
> Thanks,
>
> Bruce King
> www.ecobuildnetwork.org
> (415) 987-7271
> follow us on Twitter: @EBNetwork
>
>
>
>
>
> On Dec 23, 2010, at 9:29 AM, Derek Roff wrote:
>
>  What about moisture issues with Rastra, and other insulated concrete form
>> (ICF) systems that use expanded polystyrene?  ICFs are recommended by many
>> people for below-grade work (pun intended).  Yet expanded polystyrene can
>> take on a significant amount of water.  I'm imagining that this could
>> compromise the foam, through cracking and spalling, as well as reducing the
>> insulation values.
>>
>> Is this a problem, or have the manufacturers found a way around it?
>>
>> Derelict
>>
>> --On Thursday, December 23, 2010 9:01 AM -0800 John Swearingen <
>> jswearingen at skillful-means.com> wrote:
>>
>> I worked as a volunteer on a project with Rastra, a temple with high
>> walls.  As Derek says, it's difficult to love--the dust is awful and the
>> blocks are, well, grungy blocks.   This was probably one of the few
>> applications where the massive concrete gridwork inside the forms made any
>> sense, but the mass is all inside the insulation, and so doesn't do that
>> much good otherwise.
>>
>>
>> It's amazing how Rastra persists as a popular choice--I think it's because
>> at first look it seems like Legos.  I've had to deliver my rap on it several
>> times to clients who were initially enamored with it.  I wouldn't build with
>> it.
>>
>>
>> John "RastraRap" Swearingen
>>
>>
>> On Wed, Dec 22, 2010 at 9:09 AM, Derek Roff <derek at unm.edu> wrote:
>>
>> I've worked with Rastra a few times.  I don't like it.  I don't believe
>> their insulation figures, even after they have scaled them back. Working
>> with Rastra gives me a powerful reminder of some negative aspects of
>> concrete and styrene, the component parts.  Cutting and shaping is possible,
>> but it produces a lot of dust.  The dust is awful to be around.  I don't
>> know if it is fair to say that the material is fragile, but it certainly
>> surprised us multiple times with sudden breaks.  Working with ten-foot long,
>> 150 pound blocks carries a significant injury risk to a small, amateur crew.
>>
>> I've worked with two different kinds of Autoclaved Aerated Concrete (AAC)
>> blocks.  They are more pleasant to work with than Rastra, for me. The ones
>> that I used were very consistent in size and shape, with crisp edges and
>> corners, which could be chipped in handling.  A few blocks cracked when
>> dropped, but they seemed fairly strong.  I have concerns about the embodied
>> energy, the need for two different kinds of massive kilns to make them, and
>> their insulation claims.  It seems like every company talks about the
>> amazing properties of their 2 pounds per cubic foot blocks, but the ones
>> they actually sell have a higher density, which they often don't list.  The
>> ones that I have used are still pretty light, but very different from what
>> the industry keeps promising.
>>
>> AAC blocks have a very rectilinear, industrial feel, which is the
>> antithesis of the organic houses that I like.  But is seems reasonable to me
>> to consider this option for foundation/stemwalls.
>>
>> Derelict
>>
>> Derek Roff
>> Language Learning Center
>> Ortega Hall 129, MSC03-2100
>> University of New Mexico
>> Albuquerque, NM 87131-0001
>> 505/277-7368, fax 505/277-3885
>> Internet: derek at unm.edu
>>
>>
>> --On Wednesday, December 22, 2010 10:41 AM -0500 Chris Magwood <
>> chris at chrismagwood.ca> wrote:
>>
>>
>> Hey all!
>>
>> I'm wondering if anyone out there has much or any experience working
>> with Autoclaved Aerated Concrete (AAC) blocks and/or Rastra blocks
>> for foundations?
>>
>> Neither product is readily available here in Canada, but I'm
>> preparing some info on insulated foundation options and would like to
>> include something about these products if I can get some info. I've
>> obviously web-researched both, but I'm looking for actual
>> experience... did they meet your cost expectations, were there
>> peculiarities about the install process, how would you rate them
>> environmentally, etc?
>>
>> Feel free to respond to me off-list, as I know this isn't exactly SB
>> stuff. However, I'm hoping that among the vast experience included on
>> this list would be some hands-on stories about these materials.
>>
>> Happy holidays!
>>
>> Chris
>>
>>
>>
>> _______________________________________________
>> GSBN mailing list
>> GSBN at greenbuilder.com
>> http://greenbuilder.com/mailman/listinfo/GSBN
>>
>>
>>
>>
>> --
>> John Swearingen
>> Skillful Means Design & Construction
>> 2550 9th Street   Suite 209A
>> Berkeley, CA   94710
>> 510.849.1800 phone
>> 510.849.1900 fax
>>
>> Web Site:  http://www.skillful-means.com
>> Blog:         https://skillfulmeansdesign.wordpress.com
>>
>> _______________________________________________
>> GSBN mailing list
>> GSBN at greenbuilder.com
>> http://greenbuilder.com/mailman/listinfo/GSBN
>>
>
> _______________________________________________
> GSBN mailing list
> GSBN at greenbuilder.com
> http://greenbuilder.com/mailman/listinfo/GSBN
>

-- 
John Swearingen
Skillful Means Design & Construction
2550 9th Street   Suite 209A
Berkeley, CA   94710
510.849.1800 phone
510.849.1900 fax

Web Site:  http://www.skillful-means.com
Blog:         https://skillfulmeansdesign.wordpress.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sustainablesources.com/pipermail/gsbn/attachments/20101223/ac2e5601/attachment.htm>