MJA Roofing:: Roofer and Roofing Services in St Neots, Huntingdon, St Ives, Ramsey, Peterborough, BedfordCambridgeshire and Bedfordshire
DEFECTIVE POTS AND FLAUNCHING
Chimney pots are held in place by a great glob of cement-rich mortar, the flaunching, which also acts as the weathering
for the top of the stack. The flaunching decays more readily than the pots, usually by frost action. It is a simple matter
to replace the flaunching but take care not to damage the pots when trying to clean off the previous hard cement mortar
Damp causes problems however it enters a flue, whether the flue is in use or redundant. The moisture combines
with sulphates deposited inside the flue as a result of combustion to form weak acids. These acids attack the lime
in the parging and the mortar joints, as well as the brickwork itself. They also form hygroscopic salts (salts which
There are two basic causes of damp in chimneys: ingress of rain, and condensation.
Moisture which condenses can cause a problem in flues that remain in use. The burning fuel produces water vapour.
If the flue is very tall, wide or particularly cold, the flue gases may cool to the point where the moisture vapour condenses
within the flue. This happens particularly when wet fuels such as freshly cut timber are used.
Condensation-related damp can usually be reduced by introducing a flue liner, as this both adds some insulation to
the flue and reduces its surface area.
Ingress of rain
There are three likely routes by which rain can enter the structure: simply down the flue and into the building; around
defective flashings between the chimney and the roof; or through the wall of the chimney stack itself where the fabric