Had my guttering replaced a few months ago. Also added a downpipe as my
neighbour whose downpipe used to be between our poperties moved his to the
other end of his house so the water from both our roofs collected over my
Check to see if the downpipe is blocked at the top outlet (where it joins
the gutter) - usually with leaves, etc. This will cause water to run down
the outside of the pipe, or on the wall itself. Check that any downpipe
unions are sealed and/or fitted correctly (i.e. upper fits inside lower).
Without tackling the source you only seal in the damp to create worse
problems later. As already suggested, check the guttering/downpipes near the
damp patches. Has the outside wall been rendered 'across' the DPM? This can
allow rising damp to 'jump' the DPC and carry on up the wall. Is there
anything against the outside wall which will cause damp - a heap of sand, a
pile of bricks, a lean-to, flower bed, etc.? Is there an open chimney? Has
the wall had a DPC repaired and not been re-rendered? Old damp render and
plaster should be removed to a metre above the line of damp and reinstated
with waterproof rendering to allow the wall to dry out without affecting any
new internal plaster. Old plaster forms hygroscopic (water-attracting) salts
which continue to absorb moisture from the air even if the source of damp
has been cut off so it should always be removed rather than just 'sealed'.
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