- Q.I am installing a fence
with pressure-treated 4x4 posts. Is there any advantage
to installing a base of crushed stone at the bottom of
the post hole? If I partially backfill around the post
with concrete, will the concrete hold the fencepost
more firmly, or will it encourage the fencepost to
rot?
A.Paul Fisette
responds: In general, pressure treated wood
will not rot. The chemical treatment is poison to
the decay organisms that attack wood. Most treated
wood is Southern pine, which is an easy-to-treat
species. Although the chemical penetrates deeply
into the wood during treatment, the heartwood is
somewhat resistant to penetration. So if a 4x4 is
cut from the central portion of the tree, the
innermost core of the 4x4 may not be completely
impregnated with chemical, so the core could
rot.
I think that it is best not to set posts in
concrete. Pouring concrete around the post may save
time backfilling and tamping, but it will trap
water around the post. This could lead to core rot,
and may encourage carpenter ant infestation.
Instead, backfill the post hole with free-draining
soil or stones to encourage drainage. The best way
to ensure that fence posts are firmly seated is to
dig deep post holes.