The most important part of any paint job is called surface preparation. I dont care how good a pint you buy or how much you spend on it, if you dont have a good surface to apply it to, its not going to last. That means that the surface has to be properly primed as well, as the primer is what bonds the substrate and the paint together.
While it is possible to paint many surfaces without priming them first, its not advisable. There are several things that primers do, which paints aren't really designed to do. While many manufacturers are now advertising their paints and paint and primer in one, the reality is that those paints still dont do as good a job as a true primer will.
Quality paints are designed for coverage. More than anything, that means putting a thick coat of high pigment, high solids paint on the surface, which will cover up whatever is underneath it in one coat, so that you dont have to go back and do it again. At the same time, these paints are designed to remain somewhat flexible, so that they dont crack and bubble over time.
An unprimed surface causes serious problems with the paint being able to cover well. Most substrates used in construction are porous, so some percentage of the paint soaks into the substrate and is not available to provide cover and weather protection. The more porous the surface is, the less paint remains on the surface to cover and protect from the weather.
Primers are designed very different than paints; with the main goal of soaking into the substrate and sealing it. By doing that, they make it possible for the paint to stay on the surface, where it can provide the most protection to the building.
Another reason for using primer is that not all substrates are compatible with all paints, or even with any paint at all. Aluminum, for example, doesn't bond well with any paint. By using a special aluminum primer, you create a chemical bond with the aluminum substrate, providing a good surface for the paint to adhere to. Properly primed aluminum will allow the paint to last for years longer than applying paint directly to the aluminum substrate.
Some primers also provide a stain hiding capability, which is often necessary when repainting a home. Mold and mildew, water stains and childrens artwork on the wall are all serious problems which paints have trouble covering. It is not the color of these stains that causes the problem, but rather the fact that these stains actually seep through the new paint, staining it. A sealing primer dries fast enough to prevent that, trapping the stain in the substrate.
When picking a primer, you have to be cognizant of the reason you are priming. For new construction, this is usually to promote good adhesion and long paint life. Those reasons can apply to repainting as well, plus the problem I just mentioned about stains. You must also be sure to understand the substrate you are painting over, as that makes a huge difference in primer selection.
This is a synthetic shellac primer. The great thing about shellac as a primer is that it dries extremely fast, preventing stains from soaking through. I've personally Zinsser "bulls-eye" products for years, with excellent results. Read Full Review
Zinssers line of stain covering primers is the best in the market. If you have a stain to fight, then theyre the company you want to do business with. This is a synthetic shellac primer. The great advantage to that is the fast dry time of shellac, not allowing the stain an opportunity to soak into the primer. I've used Zinssers products for years to block stains, with excellent results. While many people use it for merely spot stain blocking, it is an excellent primer for everything else as well. Excellent adhesion to almost all surfaces ensures long life and it is even capable of blocking odors as well. Cleans up with isopropyl alcohol (rubbing alcohol)..
It's hard to say if Kilz or Zinsser is the number one brand out there. I've picked this Latex primer from Kilz because it is easier to clean up. However, they also have shellac primers, just like Zinsser does. Read Full Review
Kilz produces a wide variety of specialty primers. Like Zinsser, some of their primers are shellac based, providing the same stain hiding capability. This one is a latex primer, which has been created to provide the same advantages as a shellac primer, with the convenience of water cleanup. While I cant say that it quite matches shellac for difficult stains, it still does an excellent job in most cases. Although latex based, it can be top-coated with either latex or oil-based paints.
This is also a waterborne stain killing primer. While a little more expensive than either Zinsser or Kilz's products, it is a high quality primer, which works with almost any material. If you're trying to get paint to stick to a difficult substrate, look to Pratt & Lambert. Read Full Review
This primer, from Pratt & Lambert, is specifically formulated so that it can be used both indoors and outdoors. It bonds extremely well to almost any substrate, including such difficult surfaces as masonry, aluminum and PVC pipe. Please note that some of these surfaces may require special surface preparation for optimum sealing. Another difficult surface that it works extremely well for is repainting over existing high-gloss paint. It is a high pigment, stain hiding primer, which eliminates the need for a separate stain blocker. Fast drying, it can be top-coated with both latex and alkyd paints.
This product by Benjamin Moore is a normal primer, meaning that it is not intended to be a stain killer. It is designed to provide you with a surface just like you would have with new construction, so that your paint job comes out fresh and good. Read Full Review
For a normal primer, which isnt specifically intended to be a stain hider, Benjamin Moores Fresh Start is an excellent product. This primer is formulated to provide a surface for painting, as if you were working on new construction. Thats great when youre trying to repaint something, especially if there are problems with the previous paint. It is a low VOC product, which dries quickly. Fresh Start provides excellent adhesion and sealing in an easy to apply product.
Concrete, cinder block, brick and other masonry surfaces provide their own painting challenges. These surfaces are highly porous, absorbing paint. Sealing them requires a specially formulated primer, which can close the pores and provide good adhesion. Read Full Review
For my last pick, I've changed directions slightly. This is a specialty primer, designed for use on masonry and concrete. These surfaces are highly porous, absorbing paint just about as fast as you can apply it. Without the right sort of primer, its easy to waste a lot of paint sealing off the surface of masonry surfaces. The other problem is gaining good adhesion, as some masonry surfaces are fairly crumbly (like mortar). This primer also acts as a bonder, helping to strengthen these surfaces and help them to last longer. Moisture in the masonry can wreck havoc with paint as well, causing it to peel. With this primer, your paint will have optimum adhesion to these difficult surfaces.