What is the purpose of primecoat?

Answer 1

It depends... but here are a few examples and which primer to use.

Drywall Primer: This primer's purpose is to seal new drywall so that the next 2 coats of paint end up creating a nice even finish. If you don't have access to drywall primer you could always just use regular paint… however it is best to use a flat finish paint since it dries faster and has a rougher finish which will help make the papered drywall and joints blend in better.

Bonding Primer: This primer's purpose is to create adherence between a surface and a finish paint that would normally not have been able to stick well together. Metal Doors and surfaces with existing Oil Paint (if you want to go with a Latex top coat) are 2 examples of surfaces that would required such a primer. Before applying a bonding primer you should also scuff sand the surface so to allow better adherence of the bonding primer.

"Grey" Primer: Those primers are essentially plain drywall primers to which you add various shades of grey. The purpose of those primers is to serve as an undertone for darker/brighter colors. Darker/Brighter colors tend to not cover as well and never really end up giving the surface a 100% coverage. It is best to consult the paint manufacturer from where the color was choosen to identify which "grey" primer to use. I write "grey" in brackets because the range of grey primers goes from White to Dark Grey.

Oil Primer: Oil primers are mostly used outside on bare wood. An oil primer takes more time to dry (compared to latex primer), giving it more time to penetrate the wood and create a good bond for the finish paint.

Hope this helps :)

Happy Painting