Why shouldn't I add the additive to the rust sealer or AG111 and close the lid?

NEVER do this--it's a hazard. Once the additive is added to the rust sealer and mixed in, you should never close it up and let it sit for any amount of time. The contents build pressure and the container could blow. We recommend adding the additive at a 4:1 ratio in a separate container for the first coat, and then take out of what you need for the next coat and add the additive in a separate container. DO NOT ATTEMPT TO STORE RUST SEALER OR AG111 WITH ADDITIVE MIXED IN.