Q I was shopping for lumber for a new deck and
noticed preservation treatment levels of .21. This
seems low. Is it good enough?
Al Jacobs, via e-mail
A It depends 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.
Click Image to enlarge.
When you’re buying treated lumber, look at the tag on the end
to find out the type of chemical treatment and the preservation
retention level.
