There are two commonly available inexpensive materials that will kill rot in wood and prevent its recurrence. First, there are borates (borax-boric acid mixtures) which have an established record in preventing rot in new wood and in killing rot organisms and wood-destroying insects in infested wood.
Second, there is Glycol, most readily available as auto antifreeze-coolant. Glycol is toxic to the whole spectrum of organisms from staphylococcus bacteria to mammals.
Ethylene glycol and propylene glycol are clear liquids used in antifreeze and deicing solutions. Exposure to large amounts of Ethylene Glycol can damage the kidneys, heart, and nervous system. Propylene Glycol is generally regarded as safe for use in food. Antifreeze that is sold as “Earth Friendly”, “Environmentally Safe”, etc are generally based on Propylene…Make Sure You Buy The Propylene Glycol, NOT the Ethylene!!!
Source of Information : Agency for Toxic Substances and Disease Registry (ATSDR). 1997. Toxicological profile for ethylene glycol and propylene glycol. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
Both borate solutions and glycol penetrate dry and wet wood well because they are water-soluble; in fact, penetration by glycol is especially helped by its extreme hydroscopicity — its strong attraction for water. For both, the fact that they are water-soluble means they are not permanent solutions to rot in wood that is continually exposed to water-below the waterline and in ground-where they will eventually be extracted-dissolved out.
I have had good results by adding a water soluble “Sealer” to my solutions which make them more water resistant.
There are two types of borate products commercially available for treating wood, Tim-bor®).. A powder you mix with water and spay apply to all wood including studs, crawl spaces, sub floor, rafters and exterior sheathing. It provides a termite and rot resistant envelope treatment that can last for 30 years or more.
Treating an existing problem is best done with Bora-Care®).. It is a liquid concentrate that is mixed with water and sprayed on the affected wood and all of the wood surrounding that area.
Their equivalents and more concentrated solutions can be easily prepared from borax, boric acid, and antifreeze at much lower cost.
Glycol by itself has one big advantage over solutions of borates in water. Glycol penetrates rapidly through all paint, varnish, and oil finishes (except epoxy and polyurethanes) without lifting or damaging those finishes in any way. You can treat all of the wood without removing any finish. Once bare wood has been treated with glycol or the borate solutions and become dry to the touch it can be finished or glued. If a borate solution leaves white residues on the surface, it will have to be washed off with water and the surface allowed to dry.
Glycol’s toxicity to humans is low enough that it has to be deliberately ingested (about a half cup for a 150 lb. human); many millions of gallons are used annually with few precautions and without incident. It should not be left where children or pets can get at it, as smaller doses would harm them. The lethal dose of borates is smaller than of glycol, but the bitter taste makes accidental consumption less likely.
BORATE WOOD PRESERVATIVES: COMMERCIAL AND HOME-BREWED
Commercial:
Tim-Bor®: Solid sodium octaborate; dissolves in water to make approx. a 10% solution containing 6.6% borate (B2O3); about $13/lb. Covers about 200 sq ft.
Bora-Care®: 40% solution of sodium octaborate in ethylene glycol; 27% borate content; $90/gal. for the concentrate.
Home-Brew Water Solution of Borates:
Based on U.S. Navy spec. of 60% borax-40% boric acid (this ratio gives the maximum solubility of borates in water);
#1. This is equiv. to Tim-Bor®… 5 Qts water, 3 pounds borax, 2 pounds boric acid.
To make this solution mix the required quantities and heat until dissolved.
The boric acid, in particular, dissolves slowly. This solution is stable (no crystals) overnight in a refrigerator (40°F.), so can be used at temperatures at least as low as 40°F.
#2: This is equivalent to Bora-Care® diluted with an equal volume of glycol to make it fluid enough to use handily;
1 Gallon glycol antifreeze, 4 1/2 pounds borax, 3 1/2 pounds boric acid.
To make a stable solution you mix the ingredients and heat till boiling gently. Boil off water until a candy termometer shows 260°F. This removes most of the water of crystallization in the borax. This solution is stable at 40°F and has a borate content of 26%. This is equivalent to Bora-Care® at about $90/gal. for the concentrate which makes 2 Gallons.
A portion of the contents for this article appeared in the Fall issue of Classicboat.
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