I don't weigh it out I simply start by putting some dilute disinfectant in a large yogurt pot leaving space to add the powder. I use Vanodine V18 diluted to the surface disinfection rate. Add a squeeze of washing up liquid for wetting (not too much, half a teaspoon is fine) then slowly add the Diatom powder mixing as you go to form a smooth thin batter consistancy which paints well. Paint on the roosts and into corners where you get RM. The Vanodine disinfects and isn't deactivated by dirt.
Poultry Shield is really a detergent which has disinfecting properties (as all detergents do in fact) so you can use it though it has no disinfecting action once dry. In fact PS is an expensive way to clean your house. Cheap washing up liquid diluted with a slurp of household disinfectant is equally good at much lower cost. Better to use Vanodine though as it retains it's disinfecting properties when dry. It's based on iodine and is the disinfectant of choice for pigeon lofts and poultry houses.