The effect of steaming prior to pressure treatment on the penetration of borates into western hemlock

The recent interest in borate treatment for the production of termite-resistant lumber has led to the need for improved treatment processes. Pre-steaming prior to pressure treatment is known to have a number of potential benefits in terms of improved permeability, moisture distribution, and effectiveness of the vacuum. This process was therefore tried on western hemlock dodai (105-mm squares) in an attempt to achieve 80 percent cross-sectional penetration with a minimal diffusion period after pressure treatment. Western hemlock pre-steamed to a core temperature of 82?C in 4 hours took up almost double the amount of treating solution of end-matched unsteamed samples. There was an improvement in mean heartwood penetration of 45 percent immediately after treatment and a 134 percent increase in penetration after 1 week of storage. This was not entirely due to diffusion within the wood but to mass flow of treating solution continuing after the end of the pressure process. After 1 week of storage, 64 percent of samples had 80 percent of the cross section penetrated. Reducing the vacuum time from 30 minutes to zero had a detrimental effect on penetration. Increasing time under vacuum to 60 minutes provided no beneficial effect. Pre-steaming of hemlock dodai therefore appears to be a very effective means of improving uptake during pressure treatment.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member