I remember reading that you should mix pva glue with water when basing but wasnt sure how much, I generally paint pva glue on straight out of a bottle of elmers.
Check out this guy http://www.youtube.com/user/RubbishInRubbishOut he has some good stuff and tutorials PVA it depends on what you are using it for 50 50 is alright for scatter neat for gluing solid objects down. Redeyefrog