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My first aluminum ingots. Mine was fashioned exactly like the king of random's. And worked exactly like his did. I've melted about 200 cans and have 20 ingots. One thing I found is to add charcoal as you're working and especially right before you pour. It keeps it hotter and therefore pours better.
Buy a hair dryer, use higher grade masonry and reinforce with wire or rods
Have a machine shop make you one
You should start all over. It should set up within 15 minutes.