[GSBN] Looking for experiences with AAC and Rastra

[Graeme North]

Hi  John - I miss your point -  the mass should be inside the insulation to give thermal mass effects for moderating swings of both heat and "coolth"



Graeme
Graeme North Architects
49 Matthew Road
RD1
Warkworth
tel/fax +64 (0)9 4259305
 
graeme at ecodesign.co.nz
www.ecodesign.co.nz


On 24/12/2010, at 6:01 AM, John Swearingen 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
> 
> 
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> 
> -- 
> 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
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