"Muddymike" wrote:
[snip]

Incidentally! What are those "loft boards" made of? I had sparks coming
of the router cutter when I cut the rebate!

Floor sweepings. The sparks are from the bits of metal (saw teeth, bolts,
screws, washers, bits of wire etc) that get picked up and dumped into the
hopper alongside the chips from thicknessers, saws etc. it kills router
bits.