I hope he continues on and works through the lost foam problems.
1. I noticed he says he used premixed joint compound. All the premixed joint compounds I've looked at contain latex. Better get the dry mix bags and mix those. All of US Gypsum's dry joint compound ingredients are refractory for aluminum (gypsum, clay, mica, etc).
2. Drying. You can get 90 & 60 minute drying time dry mix compounds as well as the overnight products. My local Home Depots have the different bags next to each other.
3. Foam and wax coatings are CHILLS. Not as big a chill as a steel core, but still chills. Takes energy to burn off (melting point of styro is 250F). This energy must come from the Al. Ergo, pour at higher temperature than usual, around 1450 F.
4. Us'uns small scale foundrymen aren't exempt from the rules GM's foundries must follow. Lost foam molds have to have properly sized insulated sprues, gates and runners. And insulated riser sleeves for larger parts. You can make insulated sprues and risers from hydrocal gypsum plaster and PVC pipe molds, (not plaster of paris). These 25% - 50% 'melting losses' are a pain but are the difference between successful and failed castings. The larger the part the more critical this all becomes to avoid shrink cavities.
Pouring aluminum is far from rocket science, but there are basic rules that have to be followed for consistent success.