[GSBN] Looking for experiences with AAC and Rastra

[David Arkin, AIA]

Hi All:

We've used PISE (earth-cement) and ARXX (an insulated concrete form system) for retaining below grade (both engineered by Bruce King, come to think of it) with success.  The key to these (or any) material below grade is in the waterproofing and subsurface water control, which for us most typically includes Paraseal (bentonite clay) and a drainage structure leading to a perforated drain pipe at the footing.  

In any case assume that some part of it is going to get wet at some point, so materials that are damaged by moisture shouldn't be used.  I don't believe that precludes Rastra or AAC, as both are reasonably moisture resistant.  I've heard similar criticisms of Rastra being a pain to work with (heavy, cumbersome, etc.).  

The ARXX systems allowed us to use 8" of concrete where a standard poured wall would've been 12"; this was for a project with 10'+ retaining walls (not a Bruce project), saving us 33% of the concrete.  

I myself like the Tridi System (aka Insteel 3-D) for insulated walls below grade, as it puts the insulation in the middle and protective coatings on the outside.  One has to increase the thickness and reinforcing on the retaining side for taller walls.  I'm also intrigued with shallow, frost-protected footings instead of basements to get below the frost line, but we don't have much occasion to need these here in California.

Holiday Cheer!!

David


On Dec 23, 2010, at 11:18 AM, John Swearingen wrote:

> 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
> 


*  *  *  *  *
Arkin Tilt Architects
Ecological Planning & Design

David Arkin, AIA, Architect
LEED Accredited Professional
CA #C22459/NV #5030

1101 8th St. #180, Berkeley, CA  94710
510/528-9830
www.arkintilt.com

"There is no way to peace. Peace is the way."
— A. J. Muste 






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