Water absorption and desorption of non treated, pressure impregnated, and pine oil treated glulam made of small diameter Scots pine and Norway spruce
H Heräjärvi, V Möttönen, R Stöd
A growing proportion of harvested timber originates from the first or second commercial thinning stands in Finland, which means smaller average log volumes in comparison to final felling stands. Smaller log volume means challenging wood properties such as higher proportion of juvenile wood and sapwood. Due to these facts, products made of small diameter logs are prone to twist and check, and have reduced durability against weather. The objective of the study was to define the water absorption and desorption velocity of non treated, pressure impregnated and pine oil treated glulam.
The 6 inner lamellae of the glulam beams originated from small-sized logs, whereas the surface lamellae were made of larger logs. Beams with 44 x 200 mm cross cut dimensions were glued using MUF resin and divided into three treatment groups. Treatment 1 was not impregnated, treatment 2 was impregnated into AB class with copper-based preservative in commercial pressure process, and treatment 3 was impregnated with pine oil using the process of Ekopine Ltd. After the treatments, 20 pieces of 200 mm-long specimens were sawn from each treatment group. The cross cut surfaces of the specimens were sealed using waterproof varnish to ensure that the water movement took place via the side surfaces of the specimens. The air-dry specimens (MC 7.7–12.6%) were immersed into water for 6 weeks. After that, they were brought to a standard climate (65% RH, 20 C temperature). Again, their mass was recorded until it did not change anymore.
Pine oil impregnated glulam resisted the water absorption more than non treated and pressure impregnated glulam. Due to the low initial MC after the absorption period, pine oil impregnated glulam dried rapidly below 20% MC, while the drying of non treated and pressure impregnated glulam to the same level took 3-4 weeks. In conclusion, pine oil impregnation of timber from small-sized logs can be considered an effective and ecological preservation method for timber used in outdoor constructions. For load carrying structures, pine oil impregnation appears to be an efficient way to maintain the MC of wood below the level that enables mould growth.
Keywords: absorption, desorption, pine oil impregnation, Pinus sylvestris, pressure impregnation