Make sure you read the instructions. I don't know what version you purchased, but the Marine Tex that I use is mixed 5 to 1. Not 50/50. I mix it in small batches almost daily for the quadrajets I am building, and I just guess at the mixture proportions. It has always done well for me. If the mix is wrong, then it won't set up correctly, but it doesn't have to be perfect to work well. It should be pretty thick when mixed properly.