hi mico ballons will weaken a body, when you pour and the foam rises blok your pour whole and vent. that will make the foam to collapse the bubbles and create a very hard outer shell.as for paints that will not affect a foam body.we use a 15lb ridid and never have your issue.
we are in canada. box stores sell it in many forms.it cutseasily,sands easily.it holds screws better then pine,s .yes some folks have sensivity..the best cedars we use is white cedar from the east coast.
sadly thats been an issue for decades. shooting candy paints will peel. even cleari coatinf.when spoons are plated it closes off metallic pores in metals..the larger spoon companies have aleways had issues ..nk spoons etc .i used to squirt 20,00 spoons a year ..when the markets tanked we just took spinner blades in to paint.
we used automotive etch primer also. the easiest way if your doing manufacturing numbers is. have them powder coated in white when ordered .you will never have an issue then..our topcoats we found best is automotive clearcoat 4to 1 mix. you need a exhaust system.