Exposed gap between brick rows

[jamesbget]

This is probably quite common but just want to know from others as never come across this before: damp has penetrated from the outside under the supporting stone of a bay window (edwardian terraced) - have removed plaster inside to expose brick in doing so i notice there is a 3cm air gap between two brick layers what was there in some places is some kind of ash, this is easily removed and now exists an air gap right to the outside and this is all away along on the same line around the bay window

what should i fill this with any suggestions?

thanks James

[meow2222]

Either lime mortar or 1:1:6. Lime mortar is 3:1 sand to lime (by volume)

1:1:6 cement:lime:sand, again by volume

NT

[Andrew Gabriel]

"Stone" window sills in edwardian houses are quite often actually rendered bricks (cement, not lime). Keep an eye out for cracks in the render which can cause the effect you're seeing (and eventually the render will break off by frost action once water gets in). Also check the drip channel on the underneath hasn't been blocked with excess coats of paint, allowing water to run back under the sill. The render coat under the window frame may not be very waterproof (original window frames were often deliberately put in place before the render set in order to make a good seal, but any replacement PVC windows which could be leaking water from the frames might well leak through the render).

[jamesbget]

[jamesbget]

the problem its not under the window pane itself but the supporting stone/cement block which was had mortar originally with carbon and ash to the brick bellow removing this layer has exposed a gap of 3cm all the way round the bay - hoping that the window is still supported by the two ends - will render as advised and seal properly checking that channel as you have advised - thanks