Fran that is really poor advice. You must never use PVA to seal a wall. It will become virtually impossible to paint over - similar to when the spread overpolishes!
Use a good quality matt emulsion paint (NOT vinyl matt) and water it down 70/30 paint/water. Only one mist coat is required.
That stuff is perfect - exactly the same stuff I used recently when mist coating my house.
I wouldn't worry too much about getting the quantities exactly right as it doesn't matter too much. Use a mixing paddle with a drill to mix it in.
Also don't worry too much about the opacity of the paint once it goes on, it will look streaky but will look ok once it's dried. Remember it is to seal the plaster and is not a decorative coat!
Also, is this paint good enough for decorative coat too? Obviously without the water...
I am wondering if I should buy a few pots as it seems to be a good price for 10l of Dulux?
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