US Navy Borax / Boric acid formula
The US navy has done a formula for timber preservation, 60% Borax 40% Boric Acid, If you search for "Borax Boric Acid US Navy" you will find it.
Having done a bit of research myself, down to the chemistry level, there is a distinct advantage in adding a proportion of Glycol to this mixture, up to 50%.The glycol is a solvent for Borate compounds, and is absorbed both deeper and faster into timber than water, it carries between and along the timber fibres, and is in itself toxic, but when dry, emulsifies, and will not wash out, but as a word of advice wear a mask, and dispose of sawdust safely when cutting timber treated with this mix.
The recipies on the net seem to be about the same, but I have found that I get a residue in the liquid mix if I try the quantities to water they show.
This is probably because I am using "Technical Grade" components, and the recipe writers seem to be extremely generous, or my concentrations are higher, so not as much will disolve, as their's may have a "bulking agent", or more water of chrystalisation.
The white residue you get when you apply borax, or boric acid, can be dusted off with a wire brush, but avoid the dust.
If the timber you have if infested with bugs, use standard glycol to kill it, make a trough in plastic sheet, and liberally spray a few times, turning over each time. Allow the top to dry between sprays, three good wet sprays should do it, stand in a buket overnight to get up the grain from each end. The bugs will last one life cycle at best, then find something nicer to eat, (put a sacrificial plank nearby).
The solution should be warmed to mix and use, and if stored, re-heated to ensure no chrystals exist. (Filter or allow sedement to settle before spraying as it will clog your sprayer). Wear a mask gloves etc use a long lance, avoid drips on you, set the spray so it DOES NOT MIST, wash sprayer thoroughly and best to use a completely plastic sprayer to avoid the acid eating the metal components.
At a push you can use car antifreeze, but test to see if the dye stains the wood - try three coats, as just one will not show up.
JG
Owner of a Woodworm Zoo in West Denmark
Slowly evicting them
p.s. leave a sacrificial timber in loft to check that it works, spray it the same as the timber, for half its length, the other half untreated, look at it every couple of years, and renew (burn the old one in a bonfire outdoors), as it should be the only timber the insects can lay eggs on, so it doubles as a trap. Note also that this mixture, is not that friendly to nails e.t.c. when wet, so WD40 any Bolts etc before spraying.