Coal slag as jointing material - Possible?

[RHennessy]

Hello all

I wrote to Tony with this before noticing there was a forum. Maybe someone out there has an opinion.
I am planning a reclaimed granite sett patio, and I’m looking at jointing materials. Does anyone have an opinion on coal slag as jointing material? This will be my first time ever taking on a project like this. I would use polymeric sand, but can’t find it in black, and I want that sharp black contrast to the stones.

The coal slag I can find is 30-60 grit, which I think is .25-.6 mm, but I could be wrong in my conversion. Excuse me, I’m American. Is this too fine? I’m hoping to make the setts as tightly spaced as possible.

[lutonlagerlout]

what would bind the coal slag?

would it not cause a mess in the rain?

you need a resin mortar with black basalt sand really

not sure of stateside suppliers though

cheers LLL