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  • From: Tvoivozhd <tvoivozd AT infionline.net>
  • To: homestead AT lists.ibiblio.org
  • Subject: [Homestead] Sawdust concrete panels
  • Date: Sat, 06 Nov 2004 12:21:30 -0800

My mail client has gone a little berserk lately. I thought I saw a question from Sasha on sawdust-cement panels he was using for wall-insulation, but the message either disappeared or was a figment of my imagination. Anyway, here's an answer.

Advantages---very cheap, lightweight, good insulation factor, nail-holding capacity, resistance to fire and insects.

Disadvantages---humidity or lack of it causes a lot of expansion and contraction, causes panel movement and cracking. Increasing the percentage of cement in the panels reduces expansion and contraction, as does coating the panel surfaces with a sealant. Making the panels smaller is another way to limit expansion and contraction---a flexible grout between them allows movement without air-infiltration. Nail vertically to the center and slanting nails horizontally toward the center, allows the latter to slip without creating cracks. A cheap panel-sealant would be Jack Bays asphalt-containing Rub-R-Slate---the formulas available for $12.00 in a post I made a day or two back

In making the panels, presoaking the sawdust in water, the panels requires less sawdust and less cement for optimum quality.

Size and condition of sawdust granules is important, Granules should be firm, and screened through a 1/4 inch screen..

Conifer sawdust makes better quality panels than deciduous-tree sawdust Good species are Norway Pine, Jack Pine, Aspen, . Poor softwood species are Douglas Fir, Juniper aka Red Cedar, and Ponderosa Pine. Hardwood sawdust in general is inferior for making sawdust-cement panels, i.e., sawdust from any wood that contains a large amount of sugars, starches and tannins. High tannin content of Red Oak makes it one of the lowest-quality panels.

You can offset poor quality sawdust to some extent by adding one-third hy volume hydrated lime per one-volume of Portland Cement. Adding one percent diatomaceous earth further improves the quality of panels from poor-quality sawdust.

Another good mix is one part cement, one part sand;, three parts sawdust, and one part clay or lime. Drying shrinkage of one part cement to three parts sawdust is .55 percent. With sand added as above, shrinkage is reduced to 14 percent. With a sand component as above, the insulation factor of a two-inchy panel is equivalent to a one-half inch fiber board.

A further improvement can be made by adding soapy water and waterglass (sodium silicate) to the mix before agitating the mix---sort of a poor man's foamed concrete withlut the use of a foaming machine. The water glass coats individual sawdust granules and semi-seals them when the water evaporates.





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