What is special about primer paint? Can you use just a white paint for it?

It depends on what you are priming. In some cases the primer is there to keep the painted surface from absorbing too much of the top coat such as new drywall. In this case you can use any leftover flat white paint and it will work just fine. In cases such as stains, a good primer is a must to prevent bleed through.


When painting over oil (alkyd) paints with the same type of paint, a good prep is all you need.


When covering oils with latex, an oil based primer is a must and all the other prep is still needed (thorough cleaning with solvent, light sanding and good wipe down).


When I restore a property, I use the cheap flat white builders grade paint to prime all new unpainted surfaces including doors and trim and in 15 years it has not let me down.What is special about primer paint? Can you use just a white paint for it?
Without priming, new wood, plaster or drywall surfaces will soak up more finish paint in some areas than in others, producing a splotchy effect, and you end up using more paint to even out the finish, which is not economical because it's more expensive than primer.





In addition to sealing the surfaces, good primers will also cover different textures like the difference between drywall and joint compound. And that's critical if you're using higher-gloss paints which tend to show those differences and imperfections more than flat paints.





A third benefit of using a primer is that it provides the finish paint a better bonding surface so it sticks to the base material much better.What is special about primer paint? Can you use just a white paint for it?
if you just use paint without the primer, your paint will not hold long to whatever surface you are painting... you need the primer to have the paint stick for longevity..
It sticks better, fills in small imperfections that will show through paint and sands better than paint. On pourous surfaces, it seals better than paint and prevents the next coat from soaking in.
If you're painting fresh drywall the primer will save you paint and work. The primer also acts as a sealer.


If you're painting bare wood, the primer will help the paint stick.


If you're painting bare steel, the primer will help the paint stick and help inhibit rust.


If you're painting on top of paint primer is usually not needed.
If you're putting latex paint on top of latex paint, with a similar or darker color, in a room that doesn't get much moisture, you can get away with just painting with no primer. In all other cases, you should use primer.





Paint is translucent -- you can see through it. So you have to use a stain-blocking primer to cover graffiti (or childrens' wall ';art';) or if you're going with a lighter color.





Paint can grow mold and mildew in damp areas -- so use a mildew-resistant primer in bathrooms.





You cannot use latex paint directly on some textured surfaces -- the're like sponges and must first be sealed with two coats of a shellac or oil based primer.





You cannot use paint on raw wood or drywall -- the surface must be sealed with primer first.





Latex paint will not adhere to oil paint -- it will peel off eventually. You have to use an oil-based primer before painting with latex.





Discuss your specific situation with someone in Home Depot's paint department, or better yet a specialty paint store. In some cases primer is unnecessary, but usually not -- and there are different primers for different situations.
Primer is used on bare wood etc, as normal paint has trouble sticking to it.





Primer gives it a thick coat which adheres to the wood, which can then be painted with regular paint.





If you put regular paint on bare wood / some metals, it'll just make a huge mess and look crap.
there are 3 basic ingredients to paint: pigment, binder and adhesive. Pigment is color, binder is what holds it together and adhesive is what makes is stick to whatever you're painting.


Primer is heavy in binder and adhesive, and that's what makes it so important to use before you put on a regular paint.


That's a rather simplified answer as there are dozens of different primers, with different formulas, but that's the question you asked.