Don’t mix the Hardner with the filler until the last minute. Apply the hardner to the spreader paddle, take the board with the filler and the spreader with the hardner over to the panel that your working on and mix it right there. This gives you an extra minute or so, sometime that’s all you need. I do bodywork in south Florida and this stuff goes off in a flash. I agree with the others, mix small amounts unless covering an entire panel
