Problem with roof tiles
The standard roof tiles on my house are 7 years old (it's a new build house), whenever we get heavy rain my patio and garden furniture gets a covering of fine black grit. This has been happening for 5-6 years and is getting worse with passing years. If I don't sweep it up when dry it gradually works it's way into the patio slabs and leaves them stained requiring a jet wash.
Does anyone one know what's causing this and how it might be remedied?
I'll try to help you figure this out, but a few questions first: Are your neighbors having the same issue? Do you know if your roof tiles are concrete or clay? When you say "standard roof tiles" do you mean that they are curved (S-shaped) and the color of terra-cotta? Any chance you could post pictures of the grit and the roof?
I doubt that the particles are coming out of the roof tile. Efflorescence from tile is almost always white, yellow or brown.