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PPT Lumber: Know What You're Buying

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Most discussions about the transition to new preservative treatments have
focused on the fact that the new treatments are more corrosive to metal
fasteners in laboratory tests, and thus hot-dipped galvanized or stainless
steel fasteners and connectors are recommended by the lumber industry.
Another change that we have noticed in our area of Southwest Virginia, as
well as spot checks in other areas, is the chemical retention levels.  

One surprising issue being overlooked is that 0.40 no longer means "Ground
Contact" for all commonly used treatment chemicals.  For example, with the
CA-B preservative, 0.10 pcf is "Above Ground" and 0.21 pcf is "Ground

For a couple of decades prior to 2004, the PPT southern pine lumber that was
readily available in local supply stores was 0.40 pcf CCA (Ground Contact).
Therefore, our opinions and observations on the excellent durability of PPT
southern pine are based on "Ground Contact" chemical retentions.  "Above
Ground" treatments for 2x_ dimension lumber were rarely seen in our area in
the past, although it was supposedly available.  Now the new chemical
preservatives are available in a variety of retention levels, some of which
may be "code conforming" but may not yield the desired service life for
critical structural components in a residential deck.  For example, a deck
ledger attached to a house-band-joist is similar to a "Ground Contact"
application because of the water trapping joints created and the likely
accumulation of debris, dirt, and soil.  Assuming that only "Above Ground"
2x_ is available in the retail stores, it is extremely likely that "Above
Ground" material will be used for deck ledgers. At least in our area, almost
all of the 2x_ dimension lumber we have purchased has been 0.10 CA-B which
is an "Above Ground" product.  This site (SEAINT) may be a good place to
share what type of treatment is being used in your area for 2x_ material.
End tags should contain the chemical treatment and retention level. 

Dr. Joe Loferski and I have published a paper on this subject in the
Professional Deck Builder magazine. If you would like a copy, please send a
self-addressed stamped envelope (one stamp) to me: 
Frank Woeste
1502 Nelson Street
Blacksburg, VA 24060
and I will send you the paper. By the way, subscriptions to Professional
Deck Builder magazine are free (

Thanks, Frank Woeste
Frank Woeste, Ph.D., P.E.
Professor Emeritus, Virginia Tech
Our next short course is:
Design of Code Conforming Decks and Inspection of Existing Decks
February 1-2, 2005 in Tampa, FL.  For details, visit:

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