A chimney is one of the worst places you can locate an antenna. They
appear to be handy, but even on an old chimney there are corrosive
gases that will really do a job on Aluminum. Gas fired furnaces are
bad, wood is worse,a nd coal is terrible.

If the chimney appears to be solid enough to hold a small antenna,
(they rarely are strong enough to hold much more than a VHF, or TV
antenna) then give all the aluminum about 4 or 5 coats of clear
Krylon. Give the coax connector and attach points several coats of
liquid electrical tape.

Even then it most likely will have to be done every year or two at
best.

Steel mast fittings will rust beyond repair within just a few months.
They'll hold, but usually have to be cut off, or will twist off when
an attempt to remove the nuts is made.

If at all possible, put the antennas some where other than on a
chimney.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com