The DIY borate solution was about 3 percent by weight, or about ½ cup of borax dissolved in a gallon of warm water. The borate concentration can be increased by adding an additional 5 percent boric acid. This variation is well proven in wood treatment, but we did not test it.

The DIY glycol borate solution was made by heating one gallon of ethylene glycol with one pound of borax, dissolving all solids. The solution was slowly heated (allow 20 minutes) to 260 F to remove all water from the glycol and the borax (borax is a decahydrate hydrate salt). We then maintained the solution at 260 F for an additional 20 minutes to complete the reaction. The resulting liquid contains both ethylene glycol and complex borate esters, is about as viscous as epoxy, and nearly odor-free.

Important Caution: heating glycol solutions involves both danger of fire (combustible liquid heated above its flash point) and potentially hazardous vapors (ethylene glycol vapors increase at high temperature). This project must be done with due caution and with active ventilation. The resulting liquid, after cooling, has roughly the same oral and dermal toxicity as ethylene glycol antifreeze and presents no inhalation hazard. For more information on toxicity, consult the Material Safety Data Sheet for Boracol, as it is very similar.

Teak treatment

Halberg-Rassey recommends Boracol, a glycol borate formulation, for maintenance of teak decks. To apply (DIY, Boracol or Bora-Care), clean and allow to dry for several days; the drier the wood, the more quickly and thoroughly it will be drawn in. Apply one moderate coat, covering about 350 square feet per gallon. This will soak in within a day or so, but will not dry on the surface for several days, so plan for fair weather. A light misting of water the second or third day can speed penetration, but no more than a light mist. Any excess will be rinsed off by the rain, or you can use a hose after about a week. Because the wood is not sealed, this will need to be repeated at least annually to prevent mold and mildew, perhaps twice a season in damp climates.

We did not test the effect of this treatment on sealant adhesion. If you are planning to recaulk the deck, either do that before treatment, or wait several months for the glycol borate solution to fully dry and rinse.