Sash Windows - gaps between external brickwork

[RK]

Hi, I am currrently refurbishing some large sash windows. The windows are out of the box.

Externally, there is a gap of 4mm from the box frame and the brickwork.

There is also a thin line of render which sits along the edge of the brickwork, but seems to have come away from the wooden frame.

Is this normal? Some say the gap should be sealed, others say it should be there to let the windows 'breath'.

If it should be sealed, is there a good way of doing this, silicone for example?

Many Thanks.

RK.

[glazier7]

you should seal around the window with a silicone joint, or a poly sulphite mastic, you will get damp and rain penitration if you dont do this