French Chalk is a very versatile filler, used in casting and composites and with many other uses in other fields, including the ornate fibrous plasterware industry. It may be added to resin to rapidly thicken it, even at small percentages by weight there is significant increase in viscosity. This means with a very small addition you can thicken a resin and prevent drainage from verticals and overhangs in laminates.
At higher addition ratios, talc (french chalk) can create an effective easy sand filler for use on laminates. Just add talc until no more can be wetted out, catalyse at 3% and apply. You can add additional catalyst to 4% to speed up the reaction and get it to set faster