Tips & Advice
Is pressure-treated lumber toxic?
When the pressure-treating process was first introduced in the 1930s, wood was treated using arsenic, a chemical that is very hazardous to those who come in contact with it. Over the years, laws have been passed that forbid the use of arsenic in the pressure-treating process, and that chemical has been replaced with alternatives that are far less toxic.
Still, the coatings that are used today might present certain risks to consumers. Heat-treating achieves the same result as pressure-treating, but it does so without the use of chemicals.
What are the benefits of pressure-treated lumber?
Pressure-treated lumber brings a couple of key benefits. Wood can suffer severe damage from insect infestation, and pressure-treated wood infuses lumber with chemicals that are designed to repel insects. Pressure-treating can also protect wood from the ravages of rot. By shielding wood from insects and rot, pressure-treating can help wood maintain an attractive appearance, and it can give wood a longer life.
What is pressure-treated lumber?
Pressure-treated lumber is lumber that has been infused with chemicals that are intended to shield against insect infestation and rot. These chemicals are usually infused using a vacuum chamber, and this process forces the chemicals deep into the body of the wood. Pressure-treating can help extend the life of your lumber by shielding it from common threats.
Is kiln-dried wood treated?
Kiln-dried wood is not necessarily treated. When wood is dried in a kiln, the process is undertaken solely to reduce the wood's moisture content. Kiln-drying doesn't require the wood to be exposed to high heat, and the process can be accomplished at low temperatures.
Wood that has been treated is infused with chemicals or exposed to high heat, and this is typically done to make the wood impervious to rot and insects.
After wood has been kiln-dried, it can be treated, but the two processes are separate and distinct.
How long does it take to air-dry wood?
The length of time it takes to air-dry wood will depend on the type of wood being dried and the climate in which the drying is taking place. It can take a green board that's 1” thick anywhere from 45- 60 days to air-dry in weather that's sunny and relatively free of humidity. The damper and colder the weather, the longer it will take for wood to air-dry. Also, types of wood that naturally have higher moisture content will take longer to air-dry.
Seasoned wood has been dried to reduce its moisture content. Wood is typically seasoned so that it may burn more easily when used in a fire. Wood may also be seasoned if it is being used as a construction material. Seasoning can be done via air drying, and it may also be accomplished by drying the wood in a kiln.
Treated lumber is wood that has been treated to protect against damage caused by rot and insects. Wood may be heat-treated or pressure-treated.
With heat-treating, lumber is exposed to high temperatures that destroy the wood's nutrients. Rot, fungi, and insects feed on these nutrients, so heat-treating creates wood that is not a suitable environment for these threats.
With pressure-treating, chemicals are used to shield wood from rot and insect invaders. To accomplish this, wood is placed in vacuum chamber. A preservative is then introduced, and it's driven deep into the body of the wood. In the past, wood was pressure-treated using chemicals such as arsenic, creating a product that could be dangerous to humans and pets. The chemicals used to treat lumber today are far less toxic.
Treated wood offers superior durability to wood that hasn't undergone this process.
What are grades of lumber?
Lumber is graded according to its quality, and the lumber with the fewest imperfections and knots will typically get the highest grade. High-grade lumber is expensive, and it's not uncommon for the price to double from one grade to the next. With this in mind, it's a good idea to avoid purchasing lumber that's of a higher grade than is necessary for your purposes.
Softwoods are graded as followed, from best to worst:
If softwood lumber is being graded for appearance, the following designations are used (listed from best to worst):
- Construction grade
- Standard grade
- Utility grade
- Economy grade
Hardwoods include woods such as oak and cherry, and they are graded based on the amount of clear material that the board provides. Hardwood grades are listed below, from best to worst:
- Clear with no knots
- Contains certain minor defects
- Contains a few small knots
- Contains knots and other defects
- FAS: This designation stands for Firsts and Seconds, and it indicates a board that is 6 inches or wider, 8 feet or longer, and 83 percent free of knots and defects.
- Select: This designation is similar to FAS, but it includes smaller boards with a minimum width of 4 inches and a minimum length of 6 feet.
- No. 1 Common: This grade indicates a board that is 67 percent clear of knots, with a minimum width of 3 inches and a minimum length of 4 feet.
- No. 2 Common: This grade indicates a board that is 50 percent clear of knots, with a minimum width of 3 inches and a minimum length of 4 feet.