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By Wurm
I am cutting the outer frame for what will be the first of eight casement windows, flush cut, and have three questions:

1. Since neither the lintel nor the windowsill are perfectly straight, what is the best sealant to use top and bottom? I a guessing I should cut the frame to be as tight as possible vertically and screw it to the lintel, in which case the gaps will be small.

2. I will cut two 1/2" pieces to mount down the exterior of each side, cut to match the wall as closely as possible, can anyone recommend a sealant such as a foam to pack in behind them to fill what will be close to the 1/2" gap between the walls and the frame?

3. Aquamac 21 appears to be quite popular judging by the archives on this site, how much difference does it really make? The upstairs windows in the bathroom and bedrooms will be open much of their lives but the downstairs only on those handful of days every few years when it gets anywhere near hot in Wales, so I am wondering if I should just install the gasket downstairs.
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By thomashenry
When I've fitted windows I've used folding wedges to secure them in place, oakum to seal up the gaps, then lime mortar and putty externally where needed.
By Wurm
I have found 1/2" oakum on amazon, I am assuming that I should place a run of it at the outside of the gap and pack in behind with NHL 5 so that the oakum keeps external moisture out of the lime.

Any chance you could post a picture of a folding wedge? I am not sure what it is, and an online search for it took me to pillows for sale.
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By Trevanion
Thomas Henry has given you the details of the very traditional way of doing it, which is also the best way if you've got the time for it. I personally put steel strapping from the side of the window frame back towards the inside, bed of silicone where the window will sit, put the window in the hole, wedge it in place, foam around the frame and wait till it's dry, take wedges out and foam remaining holes, fix frame to wall with the strapping. But I'm trying to do it as quickly and cheaply as possible, If I could spare half my life to ramming in oakum to window frames like some neanderthal, I would.

Let's put it this way, there's no reason to not put draught seals in. As it says on the tin, they keep the wind and weather out and nobody likes a howling window on a cold winter night. I personally prefer a Aquamac 124 seal on the seat of the rebate pressing against the face of the casement, it's a better seal on the face of the casement than a 21 seal, in my opinion. A 21 seal works excellently on the face of the rebate though as a wiping seal, or alternatively around the edge of the casement.

It would be interesting to see some cross-sections on what you're planning to do.
By Wurm
This is a sketch of my current plan, with the oakum and the AQ21 marked in red:
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You need to take stock before you get too far ahead, Windows are classed as controlled fittings under Building Regulations.
Wurm wrote:I should just install the gasket downstairs.

To fit draft seals or Not is irrelevant, compliance with the regs is the issue here.
By Wurm
Somebody sent the local building inspectors out to me a while back, but after looking at the old windows they pronounced that anything would be better than them and that they had no further interest.

Nonetheless it is good feedback that seals are desired since I have never seen a seal on a wooden window before. Does the seal sit on all four faces of the window, or just the three that do not include the hinge?