Assessment of the Envelope Effect of Three Hot Oil Treatments: Resistance to Decay by Coniophora puteana and Postia placenta
M J Spear, C A S Hill, S F Curling, D Jones, M D C Hale
Timber of Corsican pine (Pinus nigra var. maritima) and Norway spruce (Picea abies) was treated in hot linseed oil, rapeseed oil and a proprietary resin derived from linseed oil. The samples were immersed in oil or resin under reduced pressure at temperatures of 180°C and 200°C. Very high uptakes of the oils or resin were recorded for pine, while spruce showed lower weight percent gains, below 20%.
Treated blocks were exposed to two brown rot fungi, Coniophora puteana (BAM 15) and Postia placenta (FPRL 280). The effect of using a therm-oxidatively cured resin or a drying oil (linseed) was compared with the use of the non-drying rapeseed oil. The resin treated blocks had a lower weight loss at the end of the experiment than blocks from the two oil treatments.
It is believed that the polymerization of the resin immediately after treatment assists in reducing the accessibility of the timber to fungal decay. To assess the extent to which this is an envelope treatment, a simple variation on the BS EN113 test method was used to expose untreated surfaces. Sticks of timber which had been treated with the linseed oil or the resin were crosscut to expose un-cured faces on the end grain, and exposed to fungi in the same manner as the standard EN113 test. The effect of cutting open the envelope treatment was an increase in weight loss when compared to the equivalent fully sealed blocks.