Chemically treated dimensional lumber is still in use and has been for centuries. The preservative added to wood products may allow the material to resist moisture, insects or the effects of weathering. Safe work practices may include gloves and respiratory protection, along with careful hygiene. Consult with recommended safe work practices for handling these products.
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Common Wood Preservative Types in Older Buildings:
Creosote: Mostly used for railroad ties and marine applications, creosote is an oily bitumen derived from coal-tar. It is one of the oldest types of wood preservative and is easily identified by its dark brown - black colour and coal smell.
Pentachlorophenol (Penta): This is an oil-borne treatment, used on telephone and hydroelectric poles, industrial applications, fence posts and highway construction. Penta treated wood has a brownish colouring.
Chromated Copper Arsenate (CCA): Very recognizable by its green colouring, CCA treated wood was used for everything from wood foundations and poles, to construction lumber and decking throughout the 1970's, '80's and '90's. The treatment is still in use for some applications, but has been ceased for most residential uses as of January 2004.
Ammoniacal Copper Quaternary (ACQ): The use of ACQ as a wood preservative came about as the use of CCA was decreasing. This treated wood is used for exterior applications - playground structures, fences, picnic tables and decking. The colour can be brown, tan or off-green.
Borates - disodium octaborate tetrahydrate (DOT): Use of Borate treated wood was common in the 1950's and '60's, though it's use has increased slightly in modern application. Wood treated with borates has a soapy smell and looks crystalline on its surface. It is mainly used to prevent wood-boring insects.