Scary sharpe?

The workshop is drying out nicely now and I've started to put it all back together inside...as long as it's under the tarp it'll continue to dry out, so best guess is that Pete and I will tackle the exterior at some time in May when the weather is set to get a bit warmer. I've bought the DPM, galvanised nails, some decent quality silicone and some expensive (£6 a tube!) acrylic sealant that can be used on a damp surface, so eventually I'll replace all the sealant with this stuff. I need to order the marine ply (9mm) later on next month.
I had a go at using the 'Scary sharp' method to flatten the back of an old chisel the other day with moderately good results. It's very, very hard to prevent 'drubbing' ie: lift the handle just the merest fraction and the front has been rounded over on the supposedly flat back. I'm going to have another go soon and use the David Charlesworth method of keeping only 5o% of the blade back on the medium. I've got hold of a piece of 6mm float glass which is 60mm wide so that this shouldn't be too hard to do. This also has the added advantage that the chisel back ought to become very slightly concave, good job it's only a Marples Blue Chip that cost me the grand sum of £1 and not a rather tasty brand new 25mm LN!