Material for deep window board

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I need to construct a particularly deep window board (around half a metre) for an extruded window.

What is the best material to use? I was thinking of using a piece of 25mm hardwood ply, with a hardwood beading glued and nailed to the exposed edge.
 
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Cheers. I don't tend to get on with the cut edge of MDF. What is your method for sealing and finishing?
 
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This video is as good an explanation as any. Use good quality mr or medite mdf.


Blup
 
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Cheers. I don't tend to get on with the cut edge of MDF. What is your method for sealing and finishing?
Sand it thoroughly from 120 down to 320 grit.

if you burnish the edge with the fine grit it seals it somewhat.

contract grade mdf from builders merchants is very fluffy and is difficult to sand out the fluff.

Quality Medite or caberboard is better, Moisture resistant is better still.
 
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Cheers. I don't tend to get on with the cut edge of MDF. What is your method for sealing and finishing?

Years ago when I worked for a cabinet maker, we used to use a (clear) two pack product from Morrells to seal routed end grain MDF and then spend ages sanding it back. After a few years, he decided that it was too expensive and realised that few other cabinet makers bothered using it.

As a decorator (who for many years specialised in hand paint MDF units), if faced with, for example, a bull nose finish on a MDF window board, I sand it with 80 grit Abranet and work my way through and up to 180 grit Abranet. I then apply a coat of cheapy Leyland acrylic primer and sand it with 180 grit. I keep sanding until I see a uniform colour- that is to say, I sand 60% of the primer away. I then apply 2 or 3 coats of oil based eggshell.

I have to say Medite is better than cheap MDF and MR MDF has less grain swell when applying the Leyland primer. To be honest though, I prefer painting regular medite rather than MR MDF. The reason being that the first coat of oil based eggshell. soaks in deeper and enables me to apply a more evenly coloured first coat. With the MR the paint slides (albeit, very slightly)

The primary reason for using the Leyland waterbased primer is that it is a dream to sand. More expensive waterbased primers tend to clog the abrasives.

Contrary to what many will tell you, MDF is not perfectly smooth. There are visible (parallel) sanding lines in the face finishes. Hence the extent to which I sand it after the primer.

mdf2.jpg

The above isn't the best photo, but hopefully you can see the parallel lines.
 
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Haven’t used shellac for years, love the smell.

I once made the mistake of using Zinnsser BIN (pigmented shellac) to prime a 5m long (2m tall) cabinet. I thought that its non grain raising qualities would save me in terms of sanding time. Had I used waterbased primer, sanding time would have been about 16 hours. I ended up spending about 30 hours sanding the shellac back (in part because the paint build up is greater).
 

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