Probably going to be overengineering this but what the hell....

I've got a black power coated die cast aluminium 4cm x 6cm rectangular
plate to mount outside to a brick wall that has been skimmed and
pebbledashed, so it ain't a nice flat surface.

My screw tightening regime in these type of situations has previously
been one of timidness as die cast aluminium does not bend that well, so
am now wondering about a stiff'ish material that could go up first with
manly large screws, and then that could take 4mm screws for the smaller
plate.

But what easily obtainable material in black? I'm currently thinking
Nylon plastic, about 30mm thick - will be able to repel water and not
distort in the heat of the sun. Wood is out - unless I treat and paint it..

I only need a little bit. I had a lurk around B&Q, PoundLand and other
suspects looking at manufactured goods that I could butcher for the
material. I came across a club hammer in the 99p store that looked like
a possible, but there probably is some metal in the middle of that.

Any ideas? I suspect a trip to a Plastics Stockholder could be a bit
expensive.

--
Adrian C