[GSBN] Looking for experiences with AAC and Rastra

[Bruce King]

Aren't we all in a festive Rastra-bashing mood.

I agree with John Straube & David Arkin that the most important aspect  
of any sub-grade construction is the waterproofing/drainage system (my  
own summary, correct me if wrong).  Still, Rastra and AAC are VERY  
porous, and I just wouldn't be comfortable having them between me and  
soggy dirt.

Here's mud in your eyes, Baleheads!

Bruce King
www.ecobuildnetwork.org
(415) 987-7271
follow us on Twitter: @EBNetwork





On Dec 23, 2010, at 11:46 AM, David Arkin, AIA wrote:

> 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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