Above my new french windows (a work in progress) there is an arch in the brickwork. Because I'm bringing the frame 'forwards' by a brick's thickness, I need to fill this space flush with the wall. The plan is to put an appropriate arc of wbp ply into the gap on studs to be finished etc.
The problem is how to get the curve right. It's essentially 'blind', or I could offer a sheet of something to the wall and draw the shape on it to make a template, so I need a cunning plan. Possible solutions to date include:
1 Mould something around the opening that will set in the right shape then use that as a template. 2 Paint something on the wall that will transfer onto a sheet of something (hardboard/mdf etc) and press said sheet against the wall to get a print of the shape. 3 Trial and error using thin mdf until I get it right. 4 Make a series of closely-spaced vertical measurements and draw it as a 'join the dots' exercise. 5 Calculate the radius of the arc from its width and height, then draw it with a pencil and piece of string (might be good if the house hadn't moved a mm over the past 150 years).Unfortunately none of these seems likely to be easy or successful, but hopefully someone has solved the problem before and can suggest a feasible solution before I get the angle grinder out and cut it to a rectangle....