The Art of Plastering

Plastering Tip 2: How to mix your plaster perfectly
 Mixing plaster is not "rocket science" but there are some basic rules to follow. Always use clean water to mix the plaster as any contamination can cause the plaster to go off before you've applied it. You MUST always add the plaster to the water (on roughly a 50:50 basis so half a bucket of water will make a full bucket of plaster).
My top tip is to first add just enough plaster so that it heaps on top of the water and mix in until lump free. Then add smaller amounts of plaster by hand until the consistency is smooth and lump free ("like melting ice-cream")
  A great way to test the consistency of the mix is by standing a stick in the mix....if the stick can stand on its own then the plaster is mixed perfectly. www.plastering4u.com