He Built a Home of Sawdust/Concrete
(Page 2 of 4)
January/February 1978
by O. A. Fitzgerald
In grandfather's day the diatom was just an interesting little plant to look at through a microscope. School-teachers impressed their pupils with the wonders of nature by holding up a small pinch of diatomaceous earth and telling them it contained thousands upon thousands of tiny shells.
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Within the last decade, however, the diatom has vaulted to a top place in industry. It is used in toothpaste, silver polish, and nail polish, in purifying filters in sugar factories, as insulators in high-tension motors and electrical equipment, and as fillers in paint. Diatomaceous earth has over a hundred industrial uses, mostly in the chemical, food, and pharmaceutical fields.
Friberg found that when a small part of the cement was replaced by some diatomaceous earth and a little common clay added, a lowcost, high-insulating, fire-resistant, lightweight concrete resulted. The cost, about half that of regular concrete, varies with localities, depending on the availability of wood waste and the distance from a deposit of diatomaceous earth.
Friberg's concrete cannot carry heavy loads. But since one inch of it has the insulating value of 12 to 14 inches of ordinary concrete, it is excellent for floors and walls where high insulation is desired and the load can be carried by a veneer of bricks or boards. Sawdust-concrete can be sawed, drilled, and nailed just like wood, and is amazingly fire-resistant. Here is the mix he used: one part of cement, one part of diatomaceous earth, three parts of sawdust, three parts of shavings, and one part of clay ... all volume measurements. Since sawdust-concrete has a higher absorption rate than straight concrete, Friberg added one part of clay to the mix.
First the clay is put into the concrete mixer. If it is lumpy, the clay should be soaked overnight before use. Next the diatomite is dumped in, then the cement. After these have been thoroughly mixed, the sawdust and shavings are added.
In his house, Friberg used mill-run sawdust that had aged about a year. In his experimenting, he found that new sawdust is not desirable. Neither is sawdust that has stood so long it is white. One year's aging, he says, is about right. With the shavings, age is not important. He used them green, aged a year, and older. They all worked well.
A mixture of pine, larch, and fir sawdust and shavings was used in the house. Being run-of-the-mill, there was bark in the waste. Friberg found no objections to this, but he did discover that cedar and hardwood waste are not satisfactory.
No special equipment is necessary to put the diatom to work in home building. Friberg cast blocks and bricks in commercial precasting machinery. He also cast small and large slabs using simple forms like those used in building adobe houses. Because the concrete is so light, he poured the floors and roof of his house in one slab.
