[GSBN] Looking for experiences with AAC and Rastra

[Bruce King]

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
>
>
>
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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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