FIRST STEP – AIR DRY ON STICKS
When an oak tree is felled the moisture content is around 80%, for us to be able to craft into outdoor furniture the moisture content needs to be around 12-14%, which is about as dry as the wood will ever be outside. The process of drying the boards to the required standard is two fold.
Firstly, it is stacked and air dried on sticks. To dry out the boards slowly and evenly, they are positioned to sit on carefully dimensioned sticks, the water can then evaporate off through the gaps between the timber. If the sticks are too large the gap will increase and the wood will dry off too quickly and split, too small a gap and it won’t dry out enough. Oak tends to be air dried for 1 year for every inch of thickness plus 1 year, so a board 2 inches thick will be air dried for 3 years. Once the wood is at about 30-35% moisture it is at the fibre saturation point (FSP) where only the water in the cell walls remain and all the other (free) water has evaporated. Once the wood is below the fibre saturation point the fibres start to shrink and the timber gets increasingly harder and stronger.