Damp in bay window

15 Jan 2007
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United Kingdom
Not sure if this belongs on this forum or the plaster and rendering forum, so if it needs moving please go ahead.

We have had an on going damp problem with the downstairs bay window for a couple of years. there is damp appearing on the inside wall below the window cill along about three quarters of the length of the bay window, I have always assumed that the damp was prenetrating from around the joint between the windoe frame and the outside stone cill and have tried to reseal this joint without sucessfully curing the problem.

We are planning to get the outside of the house painted next spring, and need to sort this problem once and for all before that happens.

We got a builder to have a look at the house and he believes that the damp is actually entering above the bay window and travelling down behind the sandstone pillars befor hitting the cill area and spreading out into the interior of the room.

This theory is supported by the staining which we have on the sandstone uprights that make the bay window (see photo).

One theory is that the bell casting above the bay needs to be extended to eliminate the 'shelf' effect which may cause water to gather and leak inside.

The builder had a look at the whole bay area and couldn't really see any areas with obvious gaps or cracks, but I wondered if it was worth taking some pre-emptive action to eliminate the damp.


Cut back the bell casting about six inches and re-render it so that it extends to the edge of the above bay 'shelf'

Or :-

Hack off all the render between the downstairs and upstairs windows and re-do the lot, ( possibly would look better than trying to patch a small area?).

Any thoughts please?
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