I have Dulux EasyCare matt and want to use it as a mist coat on fresh plaster first. Instructions say to seal use "thinned 10% with water". Does that mean the mix should be 90% paint or 90% water?
"thinned 10% with water" means that you add 10% of the paint volume as water.
So if you have 1 litre of paint then you add 100ml of water, which now means you have a total volume of 1.1l of mixed paint.
BTW, stir well.