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2019 Galisteo Street, Suite N-10 A  
Santa Fe, New Mexico 87505  
505/ 982.2448  •  877/ 982.2448  

Rastra Bad Vibrations
Ed Crocker

A reader who is a real estate broker recently commented to me that adobe is now passé, that it has been replaced by Rastra-block. Another reader making the same implication noted that not only is Rastra-block easier and faster to use it is, amazingly, as environmentally friendly as any form of earthen building. I dispatched myself post-haste to the Rastra web site ( to confirm my doubts.

For the uninitiated, Rastra-block is a building system that uses recycled polystyrene (your old coffee cups from Allsup's) that are made into modular forms that are stacked and then filled with concrete. They advertise their product as "the environmentally friendly solution," and claim that it is a "sustainable," "energy efficient" and "truly 'green' building material." Very impressive. Let's take a look.

Quantifying claims like "environmentally friendly," "green" and "sustainable" is out of the question because the words have absolutely no objective value; they mean different things to different people. Worse, they have become so softened by use that any edge or intent they once had has been lost. The term "energy efficient" is slightly better because there are a few parameters that allow for comparison (check out the yellow tag on your hot water heater, for example). Still, "efficient" for the manufacturer and vendor selling a product, may not be the same "efficient" that a consumer is anticipating when the item is purchased.

To complicate matters, there are at least two types of efficiency. The most commonly perceived view relates to a product's behavior vis-à-vis the conservation of post-production energy (meaning that you get the most calories possible out of your British thermal unit or BTU if you are heating water, or getting the highest R-value possible per-inch of insulation if you are trying to keep out the cold). The other type of efficiency, which relates to the production of the item, is a bit more recondite, hidden, and subject to more than a little devious manipulation on the part of promoters. It can be quantified by the amount of energy embodied in a product.

Manufacturing is an energy-intensive process; more so for some products than for others, and is governed by a myriad of variables. Softwood plywood, for example, requires 3,790 BTU/sq.ft. to manufacture whereas hardwood veneered plywood requires 12,942 BTU/sq.ft. The difference is in transportation; the hardwood face veneers have to be shipped long distances to the mill, whereas softwood plywood is manufactured close to the softwood forests. Handling, fuel costs and mileage allowances more than treble the energy embodiment of the one over the other.

Now lets look at Rastra-block. There are lots of variables here, and I haven't a clue what it takes to collect all those old coffee cups, transport them, process them and pack them into the shapes we see on the jobsite. They claim that 85% of the product is recycled material, and that ten square feet of Rastra requires only 1 kilowatt hour of electricity to produce. Interesting spin. I would be truly impressed if they claimed 10 cubic feet, but that ten square feet may translate into a fractional cubic foot if it is, for example, 1/16th of an inch thick. The other thing they don't tell us is how much energy is consumed collecting and transporting the stuff prior to expending that 1kWh. FYI, the 1kWh is equal to 3412 BTU, so it does not take long before you're talking real energy.

Then there is the issue of Portland cement. Rastra-block, as nearly as I can tell, is about 50% concrete. To manufacture one 94-lb bag of Portland requires an energy input of 381,546 BTU. Then it has to be transported to the redi-mix plant, mixed with aggregate (lots more energy expended in extracting that), and transported to the job site. It is conservative to say that that 380K becomes at least 600K by the time it finds its way to your walls. (Portland, by the way, is roughly 11% of the volume of concrete, with 67% being aggregate and the rest air and water. On average, it takes 6 bags to make a cubic yard which translates into about 85,000 BTU/cu.ft for the Portland alone -- not counting aggregate, water and transport.) This stuff isn't green, it's gray.

How does Rastra compare with earth? I know of no statistics covering the energy embodiment characteristics for adobes, rammed earth or pressed blocks. I suspect that adobes are pretty high because of transportation costs. (They are definitely labor intensive, and I m not sure how to calculate energy embodiment derived from my favorite breakfast burritos.) Same with rammed earth. Hydraulically pressed earthen blocks, however, probably have the lowest energy embodiment of any manufactured masonry unit on the planet. Years of experience with the machines that make pressed earthen blocks have provided me with some amazing statistics, among them a cost-per-unit of three to six-cents, and extremely low labor costs because the material is only handled twice. This will be the topic of an upcoming column.

Now, lest you think that I rabidly oppose Rastra, let me clarify my position. I would have zero problem with it if only its promoters didn't try to spin its virtues with soft phraseology, platitudes and misleading statistical presentations. I don't question the results of their thermal tests (though I probably should), and I admire the cleverness of the system. What I take objection to is the tendency of Rastra promoters to market their new technology as environmentally-friendly without an honest, hard-headed analysis of the environmental costs. The planet needs building techniques that cause less environmental damage, but the bandwagon approach taken by most promoters of "green" building systems is leaving the movement with damned little credibility.

Crocker Ltd
2019 Galisteo Street, Suite N-10 A  •  Santa Fe, New Mexico 87505
tel 505/ 982.2448  •  fax 505/ 995.9877
toll free 877/ 982.2448

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