The problem with filling rotting cavities with concrete is, that if you
don't get every scrap of rotted wood out before filling, it just comes back.
It's best to just clean it out, try for drainage through the cavity to
discourage sitting water, and hope for the best.

Dave

"Rob" wrote in message
om...
I have a small cavity, 3" wide, 8" long which used to be only about 1"
deep near the bottom of an old oak. I put roofing cement on it a few
years back to provide a barrier from insects. Unfortunately, it
either didn't work or ran out over time. Now the wound is another
inch deep and shows signs of insect damage. Fresh looking wood
exposed. What would be the best way to fill this cavity? I have
heard some warnings against using concrete, but I have had several
very healthy trees removed that had large cavities filled with
concrete and appeared to be healthy. Any ideas on what to use for
fill woould be appreciated, as well as any ideas on how to treat for
the insects that are there prior to filling.