Help - matte medium problem

[jim currie]

Kevin i seal all the wood on my layout with cheep mistint outside paint to stop the weather from drying out the wood (some of the wood i have got is still green(wet) and the paint helps it from warping)and changing sizes , as far as the ballest(use local sand ) i never had a white film(never used matte medium) but i wash all my ballest before using it.
jim