When and what is pressure-treated wood used for? Keep reading to find out more.
What is Pressure Treated Wood?
Pressure treated wood is treated in a pressurized cylinder. The treating process forces a waterborne preservative deep into the cellular structure of the wood, providing long-term protection against rot, fungal decay, and termite attacks. It's used for areas that are exposed to these things, or the elements.
How do you Know what to Buy?
The numbers depend on the chemical preservative used in the treatment. Every treated board carries a label. Check it to find the type of preservative used. The preservative retention for both CCA- and ACQ-treated lumber is .25 for above-ground applications and .40 for ground contact. CCA use has been reduced, so you’re more likely to find ACQ when buying treated lumber.
However, the preservation retention is different for another common treatment, called CA-B. The CA-B treatment level of .10 corresponds to an ACQ of .25 and a CA-B .21 to an ACQ of .40.
When a project calls for a certain preservation rate, it’s usually for ACQ unless otherwise specified. Lumberyards don’t always carry each type of treated wood at each level of retention. The cost for a .25 ACQ-treated deck board is about the same as for a .40, so some lumberyards and home centers don’t want the hassle of carrying both. Instead, they often carry only ACQ .40.