I have been putting up with a slate tile product failure (on walls above hot tub and pool) that has decomposed slate into the pool. Sweeping and the pool cleaner has controlled it, but the hot tub seats and pool steps have evidence of this soft slate bonded to the Hydrazzo.

What grit sand paper do I use to sand this off? Must I use an orbital sander? Could I use a palm sander? I would be doing this dry.

One other site --> son had thrown a toy in the hot tub un-noticed for a couple of days. The metal created a 3 inch rust spot. Should I sand this away? Can I sand this away?

I ask these questions so as not to damage the surface. Normally I'd just experiment, but I don't want to screw up the hydrazzo!

Thanks! Bob