putting in sash window

[plasticpigeon]

Hello

I plan to repair and reinstall a sash window. It is a pretty bog standard layout where from the inside the sash sits inside a recess that is a half brick thick. The window is therefore set back from the face of the wall by a half brick on the outside with most of the sash box obscured by the outer skin of brick. Where wooden sash box meets the brick there is a scotia bead covering the junction. What I want to know is where the wood meets brick should there be some kind of seal or bedding of some sort??? A friend of mine that is a carpenter and fits wooden sashes uses silicone, but I would imagine that maybe trowel mastic (linseed oil and sand) or even just mortar might be kinder to the wood. does anyone have opinions on this please???

 

[MatthewC]

My new sash in a similar design had a large gap on the vertical edges and so I used some lime mortar to fill it. However, the window cill has a .25" lip where the sash meets the cill so that water flows down and away, but I added a small bead of silicon as I didn't like the gap. However, both these were done recently so may not last...

 

[Feltwell]

I'm quite a convert to burnt sand mastic - much more durable than modern silicone sealants, although much slower to apply. Don't be too fussy about the mixture, I just mix some dried fine sand (buy a bag of kiln dried block paving sand - it will last you forever) with cheap boiled linseed oil until it looks right, fairly sludgy and sticky, wet but definitely not runny.

For round the edge of window frame externally I'd say use lime mortar if the gap is big enough to need it, just to extend the line of the brickwork. If the gap is really large then mortar in some suitable fill material - bits of old roof tile are a favourite, rather than putting a huge lump of pure mortar in there.

When it's gone off then use a leaf & trowel ("plasterers small tool") to put a fillet of burnt sand mastic at 45 degrees between the wood and the brick, as per below. Don't worry when the mastic is still wet weeks later, it's funny old stuff and seems to wait until you've forgotten about it before it will finally (and suddenly) set hard.

And further back..