Homestead mailing list

[Tvoivozhd <tvoivozd AT infionline.net>]

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.