Bay Window has Damp Sill

[asperity]

We have a 1930's terrace with a bay. There was a crack appearing on the paintwork at this ground floor joint, which we painted over maybe 2-3 years ago. It then got worse and today, after some heavy rain, the area was damp. I decided to hack back the paint and plaster to see how bad the crack was. Lets just say, a lot worse than expected.The wood of the inside sill is damp and dark (rotted?).This was obviously filled before with the creamy coloured stuff
Where do I start? I will get silicone for the exterior of the window tomorrow, but the inside???
Is this an insurance job?
We bought the place 5 years ago and had a full survey at the time which highlighted nothing in this area.
I don't know if it makes a difference but there was a tiny and unhealthy fir tree outside - about 2 metres away, up until the summer but then it and its roots were taken away.

 

[dishman]

When was the double glazing installed? We need external pictures of the area above and beneath the cill and the seal around the window.

Also ansure all the external drainage holes are clear of blockages.

 

[asperity]

I think the windows are from the 1980's. There were cracks which was letting ants in during the spring, so we filled them in at the time with weatherproof caulk (the white stuff on the wall) which I never got round to painting. It was ironically one of my jobs for this week but now I've got bigger problems I think.

 

[dishman]

I do not think they are late 80's....more like late 90's. They are internally beaded (panes removed and installed internally), and the air gap in the DG unit is quite big. Furthermore the design is not as square and sharp edged as the 80s ones were.

That aside, I would look at the drainage holes channels (the slight gap between the cill and the window) and ensure they are all clean and free of debris.

Is there a decent fall on that section of the window cill? Is water pooling on the cill and flowing back towards the window? How clean are the window internal mechanisms and what is the status of the seals on the windows that open? Are the seals clean and in good condition? When you lock the window does it pull the window tight agaisn the frame and create a night seal?

A separate issue...which you cant really do anything about....is that it is not really best practice to paint external brickwork. Brickwork and mortar naturally breathes and painting a thick layer of paint or multiple layers prevents this. Overtime the bricks could spall and de-laminate. It may be a long time before it happens, but something I thought I should mention for future reference.

 

[dishman]

Any development?

Mods - this may get more response in the Windows section - maybe a move to there would help...

 

[Gazman16]

Nothing obvious on the outside.
Are you sure its not a condensation problem? (puddles on the sills in the morning)

The only things I could recommend to check are:
1. As mentioned above check that the drainage is clear and working.
2. Is there a fixing down into the brick inside the opening sash? If so take it out pump some silicone into the hole and refit the fixing. There may be some in the non opening parts too but this would require taking out some glass to check.
3. Possibly the window was not sealed onto the cill correctly, The only way to check this is to take the window out though.
4. How old are the windows and do you know who fitted them? If so you may be able to get them to come back and look at it.