I'm looking to buy a retail emulsion to seal plaster and maybe use it as a topcoat but how do I know which brand to choose out of Johnstones, Dulux, Leyland, Wilkinsons. Does it make any difference about how much water to add as the johnstones and wilkinsons says 1 part water to 4 paint and leyland is 1 part water to 9 paint and dulux is 10% water.