How many bags of plaster do you lay on in one session or hit or a whole day? I have just started and usually put one bag on in the morning and then another in the afternoon. I know this is slow after reading though some threads on this but already I think I'm getting faster and will have the confidence to do more. How long does it take before you can mix two or three bags in a big bin and get it layed on without drying to soon. Thanks