I shot some Upol reface on a truck that I am working on. The directions state to mix it 3% by volume or 5% by weight. I mixed it 400 ml to 12ml of hardener. There was a very minor additional part of hardener in the last batch. I applied it with a 2.0 tip sata gravity feed gun 2 coats over the body work. This was shot yesterday at 4pm (completion time). I left heat set at 70deg overnight. I went out this morning to find it was soft and was loading 180 sand paper. I put a short wave infra-red lamp on it and heated it, let it cool to find that it sanded better. However, it appears it does not want to feather back properly. This is a polyester filler. I know it has been sitting on the shelf for awhile. (1 year?) maybe, I was not able to find any info regarding shelf life. Will polyester hardener go bad? I scraped and sanded all the filler off and will start over. This time I will use Slick Sand. Man, today sucked!!!