how to reduce external block work skin for new window

15 Nov 2012
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United Kingdom
Hi after removing an old window I realised the internal opening is smaller than the external opening. But the new window fits across both skins and i'm now left with 40mm gaps around the sides and top of the new window on the outside. I'll try and get some pics up
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Just buy a new window and put it down to experience, you can buy make up pieces in UPvc but they look poor. Unless your window is very big it will look odd with the thicker frames. You could always sell your small window or see if the manufacturer can help you out by selling it for you for a cut?
Buying a new window wouldn't do it as the window fits perfect in the inner skin bigger window wouldn't fit
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Can you not go back to window frame supplier and get some frame add on's. Depends on which window you have to the sizes you can get. Most do a 20mm and 40mm frame extension/add on's.
as you can see its a rendered finish just wondering if i can cut down some light blocks to infill then render round and to the window?
Just come back to answer your post. Re-read post. Is it 40mm gap all round or 20mm gap all round?
Regards oldun
You need to buy a bigger window and then fit it from the outside. Then either render the reveal to cover the front edge of the frame or use pvc strips.

Or you can as you suggest bring the reveal in to fit that window however you would need to tooth out some bricks/blocks rather than simply cut slips as it will crack badly and might be too unstable even with mesh in the render.

However then you'll have a decent few bits of render to replace and its hard to patch render seemlessly so may end up with a conspicuous area.
If you dont want to alter the opening or change the frame, do as Fillapolly said, get some add ons, fit from outside then get some cover strip fitted.
Hi sorry for the delay been tied up at work . Now thinking I may weather board past the window so I could batten out and trim around the reveal.

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