I sprayed some thinned waterbased acrylic onto my dio that I'm practising techniques with. The colour is over the top of craft glued ash that is solid. After I had painted it I attached some static grass and turned it upside down and tapped it. I noticed later that some spots had exposed ash base. When I rub my finger over it the colour comes off but the ash is still solid underneath. Should I be sealing this at some point to keep the paint attached and what with and at what point ie under or over the paint. In all honesty it looks like there is areas of dried mud amongst wet mud so it hasn't ruined the affect but obviously every time it is touched more colour comes off.