Hardly any at all. It is very finely crushed. One thing I would suggest is buy some of the cheap painters plastic and put it underneath your groundcloth. Then throw it away at the end of your trip. If it rains any at all, the bottom of your tent will have a fine layer of the stuff that is extremely hard to get off before packing up.
If you have that painters plastic down first, you can just ditch it at the end of your trip.