…I’ve never used Buford blanks before,but I have seen them here in the USA as a finished board and they do seem to yellow quickly compared to Clark’s.If you’re in Oz try SouthCoast foam…where’s Rabbit when you need him? …AND change paints possibly to Liquitex or another type of waterbased paint instead of a automotive paint.This is only a suggestion,but between the blank and paint is where your problem ly.Herb