New architrave around windows

29 Jul 2016
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Lee, London
United Kingdom
Hi all,

I'd like to replace the plastic trim on our bedroom windows with something that has a little more detail, preferably a wooden architrave.

Feeling all excited and productive I pulled off some trim to see what we were working with. As expected there is a large void. Rather than fill this void with bonding and then skim, could I not simply cover with an architrave that was wide enough? My plan was to frame the window with some 2x2 (or some square edged timber) which would then allow me to fix the architrave.

Not sure if this is how it's meant to be done, hence asking for help. I've attached pictures which hopefully explain things a little clearer.

We had a quote for a plasterer to come and frame, bond and skim both windows. It came to £1,500.

Thanks for any help.


20200618_141350.jpg 20200618_141422.jpg 20200618_141418.jpg 20200618_141430.jpg
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yes you can.

it looks to me like the windows were originally sliding box sash and the brickwork is stepped on the sides for the weight box box.

you probably need to take off the plastic trim that is acting as a liner -with a new timber liner and some timber packers to create some fixing points.

then fit the architrave -when finished you will have a window reveal finished very much like it was originally.

the new liner will need to be as wide as the widest point of the wall -then you can pin your architrave to the liner and any variation of the plastering in the wall will be where the back of the architrave touches the wall -which is then caulked.
To be fair it looks a tidy job in terms of finishing off but as Notch says remove the remaining pvc trim reveal and replace with timber and finish with a suitably wide architrave, probably be more skirting board width than architrave. When I was fitting instead of foaming that void I would box it out the 2 4x2 timbers screwed together, packed off the wall level and plumb, screwed and then plasterboarded the reveal and architrave the front or angle bead bond it out and skim

I guess the window fitters couldn't plaster in this case
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you could leave the lining in place and just get a new feature architrave wide enough to cover the gap (which I agree is there from the old box-sashes which were undoubtedly the original assuming your house is like the ones opposite). Alternatively, strip out the uPVC lining, trim back the foam, and glue in some timber linings - they don't need to be more than 10-15mm wide, and as deep as the existing - just enough to catch the edge of the architrave. You can buy MDF moulded architrave in many profiles e.g. from

When you mitre wide archs it helps to dowel or biscuit the mitre joint - don't try pinning through the corner it will most likely split. A couple of small pins at the edge down the lining, but I would use an adhesive foam (e.g. instastik) to fix the archs - it will adhere well to the existing foam fill and fill any gaps. It is easier to buy a foam gun and the gun grade instastik than use the one with aerosol nozzle which is a bit uncontrollable.

If you get a joiner to fit new archs, it's only a 1/2day work - would actually only take an hour or so, say £100 ish for 1/2 day, £200** full day if there are other jobs. so don't get ripped - £1500 to sort this is BS

**just seen you are London, so maybe a little more but not so much...
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