Wood that is resistant to penetration by preservatives may
be incised before treatment to permit deeper and more uniform penetration. To incise, lumber and timbers are passed
through rollers equipped with teeth that sink into the wood
to a predetermined depth, usually 13 to 19 mm (1/2 to
3/4 in.). The teeth are spaced to give the desired distribution
of preservative with the minimum number of incisions. A
machine of different design is required for deeply incising
the butts of poles, usually to a depth of 64 mm (2.5 in.)
(Fig. 15–4).
Incising is effective because preservatives usually penetrate
the wood much farther along the grain than across the grain.
The incisions open cell lumens along the grain, which greatly enhances penetration. Incising is especially effective
in improving penetration in the heartwood areas of sawn
surfaces.
Incising is practiced primarily on Douglas-fir, western hem lock, and western larch ties and timbers for pressure treatment and on cedar and Douglas-fir poles. Incising can result
in significant reductions in strength (Chap. 5).