Half Lap Mitre with Cupped Boards
Hi all,
I'm a total novice building some floating wall mounted corner bench in my garden. I went and bought two new 3.9m standard Grade A scaffold boards from my local yard. They were all stored upright in the depot and I tried to select two that didn't have twists or bows, were nice and straight etc. They're pretty good, but all seemed to have slight cupping. It's impossible to check this easily when they're stored like that.
Anyway, I thought I would just use them concave side down and with lots of cross bettens underneath to force the crown down and keep them flat. Hopefully as they then start to aclimatise they won't twist and stay fastened down.
However.... to make that even better I'm looking at the corner of the L-shaped bench where I'm going to mitre the 4 boards together. I've started to think that this would work great as a half-lap mitre join to stop the boards curling and warping over time and the mitre looking a mess. (note that this bench area is completely covered so will never be directly exposed to elements, but still...).
So, given my inexperience am I an idiot to attempt a big half-lap mitre of 4 cupped scaffold boards??? I don't want to 'lock in' the cupped profile when I cut away half the board thickness, so I'm trying to figure out how to do the cut. I have a 165mm circular saw where I can fix the depth of the cut and then just follow the cupped surface and hopefully acheive a corresponding cupped join. It sounds challenging, but any other advice or thoughts on this? Should I fgorget about it and just do a butt jointed mitre instead and hope for the best?
The total area of the half lap mitre (4 overlapping scaffold boards) would be 45 x 45 cm, so a signficant join.
Any advice welcome.
Posted Aug 7, 2025, 12:48 AM UTC