sitting window frame/cill in opening

[MrT]

After removing my sash and replaceing rotten section I'm thinking about how best to put it back in the frame. It has a extended seperate cill, replaced with hardwood, which was orignally laying over the 2 leaves of a cavity wall with out any mortar. I'm wondering if I should put a strip of DPC and the mortar before putting it back. I've has to replace the bottom section of the frame and have used a piece of wood 1cm thinner so I can get some mortar in now.

the frame was fixed to the cill with nail knocked in from under the cill into the bottom of the frame. Is there a better method than this ie dowels T&G etc.

Many thanks.

 

[Andrew Bodenham]

The sill to stile (frame) joints are always vunerable to water ingress, as this is where water tends to pool and get sucked up into the endgrain of the stile. In many of the sash renovations I've done the presence of nails has led to early failure of the joints, due to rusting, expansion, and subsequent splitting. I'd probably use polyurethane glue, with stainless screws to provide location and clamping if required.

As for bedding the sill onto the masonry there are lots of options. You want to avoid creating a capillary crack which will pull in water, so I'd avoid bedding onto mortar. I'd probably wedge underneath with plastic packers or oak wedges, then fill with a non-setting mastic like polysulphide. Make sure there is a good drip groove (or drip batten) in the sill to stop water before it gets to the joint.

Oops - complete lack of putty, burnt sand mastic, fish glue, hand cut nails or other traditional stuff there. Bad, bad boy.

 

[biffvernon]

Yes, we don't grow polysulphide in our garden. I try to avoid anything that involves drilling holes through my window frames. Just hold them in with oak wedges and fill the gaps with lime mortar for big cracks and linseed oil and sand mastic for the smaller ones.

 

[Nemesis]

Yes, naughty, all that trad stuff, Biff, you'll be telling us next you don't use a nice cement mix for pointing.