My Review of Bathtub and Ceramic Enamel
Don't ruin your bathtubs with these bathtub enamels. These enamels are for touching up chips where there's no contact with water. There's also acrylic pouring, and it's done professionally: sanded, degreased, and then a special ceramic acrylic pouring enamel is applied. And that's not durable, not like the factory coating, where a special enamel is applied to heated cast iron in ovens.
At 2:10, I misspoke and said Monnol, but it's actually Novol 90409 (white) epoxy primer. And never buy cheap primers; they take a long time to dry, and you can ruin the surface when you apply the enamel over the primer. If the primer isn't dried properly, the enamel will tear.