system 3 quickfair

[Hoover]

Everything I have ever read about this product has been great. I bought 1 1/2 gallons and have had nothing but trouble. I mixed it by hand and it didn't set up correctly. I sanded the goop,and wiped remainder that didn't set off with acetone. Then I went out and bought a scale and mixed 7 to 3 parts exactly. I made certain to mix it and mix it and mix it some more. This new layer has been on for about thirty minutes and its not getting hard either. I went to the system three web site and read the trouble shooting problems prior to this last application and it is still just not gettin it. What am I doing wrong?