Sodium silicate wood treatment

Silicate-impregnated wood is nothing new; it's been around for at least as long as Arizona's famed Petrified Forest. While scientists once assumed that such petrification took thousands of years and tons of pressure, scientists and homeowners have found ways to duplicate the process within hours. Silicate-impregnated wood offers many advantages over both raw and pressure-treated lumber.

One of the very first instances of man-made impregnated wood can be found in Venice Italy. Venice was originally built as a sort of unassailable fort, designed primarily to defend against land-borne attacks from raiding barbarians. Venice's swampy underpinnings helped to keep it safe from such assaults for centuries, but required some outside-the-box thinking from the city's architects. These architects constructed many of Venice's huge stone structures (including the Basilica of St. Mary of Health) on huge wooden pilings sunk into the swamp beneath. Over time, those pilings absorbed many of the minerals in the water, petrifying to become true stone columns.

Sodium silicate is just one of several dissolved mineral compounds used to petrify wood. Almost any dissolved mineral can impregnate wood and turn it to stone, but silicon is among the hardest. When its water carrier evaporates away, sodium silicate (a mixture of sand and soda ash) leaves behind a fully bonded sheet of silicon glass. It is for this reason that sodium silicate is commonly referred to as "liquid glass."

When dried and oven cured at 44.4 degrees Celsius, sodium silicate bonds to the wood's fibres and hardens inside. This internal glass matrix acts like the resin in fibreglass; it makes the structure as a whole both more rigid and practically waterproof. Glass-impregnated wood is about 40 per cent stronger than untreated yellow pine, falling in between black walnut and southern red oak in terms of hardness.

While glass-impregnated wood isn't technically fireproof, it's fire resistant enough that you'd almost need sustained, direct contact with a blowtorch flame to make it smoulder. To put that into perspective, such sustained contact is of the same type used to melt steel. Additionally, water can't penetrate glass and bugs can't eat it, making glass-impregnated wood a real alternative to arsenic-impregnated, pressure-treated alternatives. Unlike arsenic, dried sodium silicate is not harmful to animals or the environment; after all, it's only sand.

You can make your own sodium silicate-impregnated wood by soaking your lumber in a 40 per cent aqueous solution of liquid glass under about 100 psi of pressure. Afterward, you'll need to oven cure it at 44.4 degrees Cor several hours (until it dries out and the surface turns clear). As of May 2010, only one company (called TimberSIL) offers pre-impregnated lumber for sale to the general public. As a basis for comparison, TimberSIL's two-by-four-by-eight lumber costs £2.90 apiece, compared with £2 for the pressure-treated equivalent at Lowe's and Home Depot.