I cannot think of any way to tell other than the greenish cast
that might still show on the bottom of the deck boards. You could
knock one of the boards loose and the portion that is in contact
with the joists should still be green. Anything that is exposed
to sunlight will be the typical gray color. CCA lumber was
typically southern yellow pine if you are good at judging lumber
species. There is a strong chance that there are lumber stamps
still readable on the bottom.
Inquiring minds wonder why you need to know. If the deck is
serviceable, why does it matter?
Keep the whole world singing . . . .
DanG (remove the sevens)
If its worth $20 bucks to you check this website out
Results are also used in a university study (double duty for your dollar)
This will only test for the older CCA (with Arsenic) PT woods. They were
only phased out last year and some retail stock still exists.
A good review of the topic here
I can usually tell by looking at it. Or if that is questionable,
shave off a slice and examine the freshly cut piece. PT lumber has a
very characteristic green color to it, although the shade of green can
vary. Also, PT wood sawdust has more of a texture similar to
cornmeal--untreated lumber does not and has more of a a furry
appearance. Is your deck lumber pine? cypress? redwood? cedar?
white oak or teak? If pine, your deck is most likely PTL.
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