B&Q probably won't help here, but a timber yard would.....they would use either a circular saw then a planer /thicknesser - hopefully for the price of a drink or a packet of fags
John
I would use a circular saw, with the guide set. Do 1 side, then the other. Keep a decent pressure on the front handle and go slow.
There will be slight unevenness when the excess falls off as nobody can cut at a perfect 180 degrees. If it matters, use an electric plane to even it out. If it won't, treat the exposed side with end seal, and fit it.
I'd recommend coach screws for fixing to wood, or Thunderbolts for fixing to concrete.
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