The top coat of a painted surface is what everyone notices. Many people assume the top coat is the most important coat you apply to a surface. The truth is the primer, sealer and undercoat are just as important. What is a primer, sealer and undercoat? A primer is the first coat of paint applied to a surface. Primer is the most important coat you will apply. A primers main purpose is to provide a base coat for the following coats of paint you will be applying. A primer provides a surface for the next few coats of paint to adhere to the surface better, primer also prevents moisture from entering into the surface you are working on as well as covering up and preventing stains. Next, a sealer is to be used prior to or in place of a primer. A sealer and primer or basically the same thing, they both provide good adhesion for the following coats as well as prevent moisture and stains. The main difference between a sealer and primer is that a sealer can bind up crumbling surfaces such as crumbling concrete. An undercoat is the next step in the painting process. An undercoat provides even more adhesion for the top coat as well as preventing moisture and stains from entering or seeping through the surface. The main function of an undercoat is to fill in and smooth out the surface prior to the top coat finish. It is important to remember that the application of a primer, sealer and undercoat is a waste of material unless the surface is properly sanded and prepped prior to their applications.