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We have discovered a damp wet patch under the bay window

We have discovered a damp wet patch under the bay window sill on the interior of property, we are having problems determining where it is coming from. Any ideas/solutions????

We recently bought a 1930's house with a bay window in the living room. Whilst removing the wallpaper under the window we found black mould which was exacerbated by the wall being covered in polystyrene sheeting. The wall under the bay window had dried out nicely and we then had the plastered knocked back to the brickwork and replastered.

Over the last week ago we have experienced some snow and rain and have noticed a damp patch appearing in the right hand corner directly under the window sill and it radiates outwards from this point. We have ruled out rising damp, as the floorboards, skirting boarding and wall are sound. Even when it was riddled with mould the plaster had not blown out. We have looked outside of the property to find a cause but we are really struggling to find something that really stands out.

The bay window is a uPVC window with a stone sill on the outside, it has no cavity wall and is stone faced. The external brickwork looks alittle mossy near the ground and some of the stone bricks feel alittle sandy on the exterior but nothing that really scares you too much.

Does anyone have any ideas/information/solutions to this problem. All help will be gratefully received.


3 Answers from MyBuilder Restoration & Refurb Specialists

Best Answer

the problem sounds like the water is crossing the stone work directly below the upvc window cill, check for holes in sealing to cill and stone work, the sealing should not be mortar as the cill expands and contract to much it should be silicone, also if the upvc cill has not been made in one complete section this could also allow water to enter where the joint is, also check the ends of the cill for holes as this could allow water to enter and run along the stone top to the lowest point which could be the area of damp, check the pointing to the stone work for soundness


Answered 12th Apr 2012

You mention 1930's build, upvc and black mould and bay window.
Whilst water ingress is a possibility, so too is lack of ventilation.
Perhaps the 'canary' you should watch out for is condensation on the double glazing. If you are getting this, it suggests lack of ventilation. All the above aspects combined make it a classic candidate.
The other thing to bear in mind as to whether or not it will become serious this winter is whether or not there are now more people living in the house than before. If it is fewer people the problem may not reach the level you inherited.
There are solutions but they are too involved and individual to set out here.
Hope this helps


Answered 23rd Oct 2013

without looking at the problem it is not really possible to give an accurate diagnoses but
check the pointing is sound it should not be cement but lime mortar on a building of this type, if the lime mortar is past its best this could be letting water cross the brickwork from the outside to the inside,or if it has been re-pointed using a cement based mortar.their is no cement in lime mortar


Answered 10th Mar 2013

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