When I first started pouring Aluminum with my homemade foundry, it was all greensand stuff. This was primarily due to a coworker donating two 5-gallon buckets full of greensand he'd picked up somewhere. However, my laziness and lack of patience got the better of me. Making intricate wood patterns to pour a one-off casting was just too tedious.
A couple weeks back, I was doing some research on homemade CNC machines and ran accross this site: www.buildyouridea.com. This guy was pouring lost-foam castings using drywall mud to forma shell over the foam patterns. This was a breakthrough for me. I knew that big lost-foam operations used some sort of dip so they could use plain sand and keep it out of the aluminum. I just hadn't figured out what would work as a homebrew dip!
On saturday, Bob and I farted around pouring some lost-foam castings to try out different things. The drywall mud dip exceeded my expectations! The surface finish was awesome! This is exciting and you can expect to see more lost-foam castings from me in the near future!
