Summary
During two years of natural weathering the course of the moisture content of test samples of pine sapwood
(Pinus sylvestris L.), Norway spruce (Picea abies L.), oak heartwood (Quercus robur L.) and Douglas
fir heartwood (Pseudotsuga menziesii Franco.) was recorded by means of 12,000 individual gravimetric
readings. The samples were untreated, treated with a weather protection varnish, or impregnated
with melamine resin. The data were evaluated with regard to the number of days per year on which the
moisture content of wood exceeded the limit of 25%. From the results of subsequent laboratory investigations
into the adsorption of liquid water and moisture vapour desorption using the same test material,
it was possible to work out a mathematical relationship (MRI = moisture induced risk index) which
correlates closely with the number of days of more than 25% moisture content during the second year
of natural weathering. The MRI is proposed as a parameter for the assessment of the protective effect of
wood treatments which are intended to reduce moisture content and also for durability prediction of
untreated wood in out of ground contact situations.
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