I get a lot of questions from furniture painters about primer. What it is, what it does and whether they should use it. I know when you get a nice piece of furniture, you are eager to get on with painting it and wonder if all that prep is necessary. If you want to produce a beautifully finished and durable item of furniture, then I believe you should.
There are several primers you can use and your choice will depend on what you are painting. Primers provide a uniform surface for your paint to adhere to, improving the look and durability of your final coat.
If you have stripped the furniture to the bare wood, shellac based primer is a good choice. It will ensure the tanins or stain in the wood will not bleed through the final coat. If you use a water based primer and the wood bleeds, it will bleed through the top coat no matter how many coats of paint you apply. In 99% of cases, a shellac based primer will stop bleed through. Shellac based primers are a good, safe choice for bare wood.
If the piece is already painted, water-based or oil-based primers are best. The rule of not painting water-based paint over oil, does not apply to primers.
100% acrylic primer is best for mdf although shellac can be used
If the piece you are painting is glossy and non-absorbent, you need an adhesion primer. This works by sticking to the glossy surface and giving you a proper substrate to accept paint.
Primer can be tinted to help cut down on coats of paint and improve the opacity of the top coat especially if going over dark colors with lighter paint. Use colourant to tint the primer, not paint. Colourants or pure pigments can be used to tint Shellac, Oil and Water-based primers. I just want to say a quick word about paint with primer already added. The idea behind this is to create a paint that has great coverage. This is used in those situations where you would use a primer to block out the existing color. It is no use for those situations where you would use a primer for stain blocking or adhesion. I hope after reading this you will understand why primer/paint is not the best choice.
The two primers I keep in my arsenal are Zinsser BIN and Whitson’s Primer. They will cope with most situations!