Chimneys in old
houses are frequently single skin brickwork with lime-mortar based joints and
pointing. Years of external weathering and internal attack by the corrosive
sulphates in flue gases can lead to gaps in the cement fillets, allowing inflammable
tars to leach into the roofing material.
A visual inspection of the exposed stack will highlight any obvious problem
areas but hidden patches within the roof can only be dealt with when a re-ridge
or re-thatch is undertaken. It's essential that when this work is in progress,
the opportunity be taken to undergo any repairs and repointing necessary
before the thatch is replaced. Reputable thatchers will do this as a matter
of course but it's in the householder's own interest to satisfy themselves
this has been done.
lead flashing indicates the original roof line. The condition of
the pointing in the area that would have been within the thatch
is dangerously neglected.
Another essential maintenance
procedure is getting chimneys swept. The following is taken from a publication by Dorset Fire
and Rescue Service:
"It is vital that flues are regularly swept. Owners should assure themselves that their
sweep is experienced in the type of fire, flue and fuel combination in use. Intervals between
sweeping will depend on the fuel burnt and the frequency of burning, but it must be a minimum
of twice a year; once toward the end of a burning season and again prior to the start of the
next to ensure a flueway clear of any obstructions, such as nests, as well as flue deposits.
If wood is burnt, the frequency of sweeping should be increased."
For information on the lining of chimneys, please see
Multifuel and Woodburning Stoves.