I drilled into the end pour tonight for a rudder installation. When I drilled the pilot hole and pulled the bit out, it poofed powder about a foot high! The bit was not hot. Why would it poof? Is the solid pour under pressure after it is cured? I think it was more poof than just hot air trapped, especially as the bit was not even warm. Perhaps there was a void that had compressed air somehow? The filler is a mix of fine sawdust and microballoons.