Once you've applied Nitromors put whole wheel in a bin bag, or if you can get hold of any shrink wrap used for pallets wrapping works well. By wrapping it up, it stops the air drying it to quickly. Then unwrap and start scraping it off. I found using a plastic card (i.e. old credit card, Tesco club card) worked very well. Just cut the edge of the card you've been scarping with when it starts to get blunt. Then rinse of with a jet wash and re-apply if it all hasn't come off.