Wood can be impregnated with a variety of preservative chemicals to prevent rot and insect infestation when used in exterior applications like building decks. Most treated wood will have a green tint that will turn to gray after couple of years of weathering. Almost any kind of wood can be treated but some types will more readily accept the treatment than others. Pressure treated lumber is ideal for outdoor construction as it has a useful life span twice as long than redwood and cedar and is much less expensive. In some cases treated wood can last more than 40 years. The treatment process involves placing a load of lumber in a huge cylindrical chamber called a retort with a door on one end that can be sealed airtight and then forcing waterborne chemicals into the wood by creating a vacuum.

Full cell pressure treatment uses a vacuum to evacuate all of the air and moisture from the wood before injecting preservative. For maximum retention levels the wood is treated to refusal or until it can’t absorb any more preservative. The empty cell process involves forcing the preservative into the wood without first using a vacuum. There are variations of both full cell and empty cell methods that work better for different preservatives to treat different types of wood. The pressure treatment process works to evenly penetrate the board which is much more effective than a dipped, brushed, or spray treatment which is more likely to leach off the surfaces as it dries.