How to fix this plaster?

Cola133

I've got an upstairs window reveal, where the plaster keeps crumbling above the window. It seems dry, so I think maybe to do with condensation and that the window tilts open inwards. How could I fix it please so it doesn't keep happening? Thank you

danrv

The blistered paint there could be down to damp either from outside or condensation.
Is there a heater under the window?
That would be the first thing to sort.
Check if the plaster has blown from the brickwork by tapping it. 
If it sounds hollow, it would be best to remove it and then patch plaster.

FreeBear

Second image suggests that there might be water penetration at the top of the frame. If there is water getting, it needs fixing first.

To fix the plaster, I'd remove all the blown areas and paint a primer on. Febond Blue Grit or similar type product. That will give any new plaster something to bond to.

stuart45

Have you got any external photos?

Cola133

stuart45 said:

Have you got any external photos?

@stuart45 these are the best photos I could get hanging out the window. Thank you for your help

stuart45

The photos are fine thanks.
It could be moisture running down the inside of the outer brick skin. Normally it runs down into the foundations, but where the cavity is bridged a tray is put in like the diagrams. When windows are replaced these trays are often damaged.

Cola133

@stuart45 do I need a builder, a damp specialist or a window person? I don't know who to contact to get it fixed. Thank you for your help

stuart45

You'd need a bricklayer to replace the tray, and possibly put in a lintel.
The first thing to do is establish that a damaged tray is the cause. It is possible to look into the cavity with a borescope during heavy driving rain, although even without the camera you should notice increased moisture when this happens.