Some instances of severe warping of siding treated with a commercial waterb
orne preservative have been reported to the authors. We investigated this p
roblem by evaluating 25-mm-,51-mm-, and 102-mm-(1-,2,-and4-in.-) thick chro
mated copper arsenate (CCA) treated No. 1 southern yellow pine lumber shipp
ed from three suppliers to a secondary manufacturer in Louisiana. The moist
ure content (MC), CCA retention, and adsorption/desorption ratio was determ
ined for specimens cut from the lumber. For all lumber thicknesses and targ
et retention levels, including untreated wood, the MC of many boards exceed
ed the secondary manufacturer's specification of a maximum of 16 percent MC
. No consistent relationship was found between CCA retention and the adsorp
tion/desorption ratio, indicating that the presence of the preservative oxi
des was not causing excessive fluctuations in wood MC. The results suggest
that the source of the dimensional instability is the initial high MC due t
o inadequate redrying.