you will want a primer with a heavy body something like those rubberized paints (rustoleum leakseal) and if you would use that it has a paintable finish so it can be done later with spray or a clear if that's enough

Hi, guys. I'm making some planters out of empty 5 gallon buckets. I spray paint them with white primer and white gloss. Issue is, when put against the light, they look semi transparent (see pic). Will grey primer make the fully opaque? Or other solutions?