It's hard to think of a more readily available, a simpler, or a less costly insulation ... yet the "R" factor (the higher the "R", the better) of each inch of cellulose fiber is a very respectable 4. Even when you buy it ready-made, then, this is an extremely costeffective insulation. And when you make it yourself your savings can really skyrocket!
That " makin' " is not in the least complicated either. as MOTHER's researchers recently proved to themselves. It mainly consists of [1] gathering together enough bone-dry scrap cardboard or old newspapers, [2] running them through a farm-type haMmermill set for its finest possible grind, [3] mixing in—either before or after the cellulose is groundenough fireproofing and vermin repellent to protect it, and [4] putting the finished insulation where you want it.
USE A FARM-TYPE HAMMERMILL
The only "complication" we've found about this whole do-it-yourself project is that nothing less than a real, live, genuine hammermill will handle the grinding of the cellulose the way it should be handled. Little garden mulcher-type "shredder grinders" simply won't chew either paper or cardboard into the fluffy, fuzzy mass of fibers that makes the best insulation. (Rule of thumb: If you can still read whole words on your ground newsprint, it wasn't ground finely enough.)
What you want to do then (if you don't already have one) is rent or borrow or barter some time on one of the feed-grinding hammermills that many farmers own (the units are very much like the leaf grinders and limb shredders that you frequently see utility line crews using alongside the road).
Take care, too, to see that all the paper and cardboard you feed through the grinder is bone dry and stays that way (moisture can cause the shredded cellulose to "compost"). And always wear a respirator mask to protect your lungs from both paper dust and fine chemical particles as you work.
That last caution, by the way, is by no means meant to suggest that the chemicals used to treat the cellulose are in any way highly dangerous. Boric acid, the fire retardant used by most manufacturers of this insulation, is—as you probably know—so mild that doctors have frequently prescribed it as an eyewash. This particular fireproofer is now in such short supply, however (because of the current tremendous demand for insulation), that MOTHER's research crew has tested and presently recommends fireproofing cellulose insulation with borax. And borax, as you're surely aware, is so safe that it's the major ingredient in some laundry soaps.
The aluminum sulfate listed here as a rodent and insect repellent can best be put into perspective when you realize that it's one of the chemicals generally called "alum" (even though the term is more accurately descriptive of a double sulfate of ammonium or a univalent metal-such as sodium or potassium-and of a trivalent metal, such as aluminum, iron, or chromium). The chemical, in short, is an astringent and, as such, may be safely handled without gloves (although we do recommend keeping its dust out of your lungs and away from your mucous membranes). Do bear in mind, however, that aluminum sulfate is highly corrosive to most metals ... and, for this reason, an equal weight of ordinary lime (which neutralizes the alum) should be substituted for half the aluminum sulfate when your treated insulation will be used in metal buildings or mobile homes.
THE PRICE IS RIGHT
As the first chart reproduced here indicates, MOTHER's researchers ground up and tested six batches of cellulose fiber ... each of which contained a different percentage of vermin repellent and fireproofing. After trying to ignite all the test mixes with a propane torch and observing the results (see chart) , we recommend that a minimum of 25 pounds of aluminum sulfate (or half aluminum sulfate and half lime) and 12 pounds of borax be mixed into every 100 pounds of ground newsprint or cardboard.
This figures out to a total chemical cost (at $8.50/100 pounds for aluminum sulfate and $15.00/100 pounds for borax) of less than $4.00 per 100 pounds of paper that is treated ... or 5¢ a square foot when an attic is filled with a 6"-deep layer of the cellulose fiber (which produces a total "R" factor of 24, and that's very good). This compares quite favorably to the 24-1/2¢ a square foot that a local contractor charges to fill an attic space with only 5" of a commercially manufactured cellulose fiber. On a 1,300-square-foot house, that's an immediate saving of $253.50 right there ... and you're getting one-fifth more insulation to boot!
The chemicals were mixed into our first six test batches by shaking them onto the paper as it was fed into our hammermill. This is exactly the method used by the commercial manufacturers of cellulose fiber insulation that we've visited ... but it does have a minor drawback: The chemicals do tend to settle out of the mix as it's handled and, if some care isn't taken, more of the fire retardant than we like to see will wind up at the bottom of any space filled with this insulation.
For this reason we tried grinding some cellulose all by itself, putting it in a pile, and then sprinkling controlled amounts of borax and aluminum sulfate across the surfaces of the fiber. We were figuring, of course, thatsince flames burn up-it would take less of the chemicals to fireproof the pulverized insulation if those chemicals were put on top of the cellulose, instead of being allowed to sift to its bottom.
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