Concrete molds?

[KretZ]

I used a plastic mold to make a patio years ago. One bag to each mold, and it worked. Now it is under another 3 feet of earth. But I have made a couple of molds using hardwood with waxed paper on the inside of the mold to make it realease, Hinges on the corners.

I am in the process of making a patio like what you describe. I had to stop when the weather got too cold to pour. Why is yours under three feet of earth now?

 

[Ed of all trades]

With many molds you need to use a release agent, so it won't stick to the mold. you might get away with it and then again you might. If you don't you just ruined a good mold. Tapping with a rubber mallet works well on many molds to release air.