Inadequate redrying linked to dimensional instability of CCA-treated southern pine lumber

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.