Sorry all, I meant asbestos / synthetic slates. I ask for 2' by 1' slates at the BM and thats all they have.
I'll post some pictures as soon as I can face the ladders, and I'll try a length of copper wire for a while as an experiment to settle the argument.
The slates you refer to with three holes, are fibre cement man made slates, known as Eternite or Fasnet. The two upper holes are for the fixing nails and the bottom hole is for the copper rivet. This rivet is there to stop the slate from curling up in hot weather and wind up lift, as these slates are not ridged as natural slate. They are noted for attracting the growth of moss in between the side joints on a low pitched roof. This is caused by the ingress of dirt holding in the side joint.
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