Do you need a primer to paint? Depends on your application. With the modern paints, a lot of times the answer is no. They are marketing all these self-priming paints, and they work pretty well. However, if you're doing a large plaster patch on the walls as we did here, you can go ahead to the store and buy a basic water based primer. They're easily labeled, and there are a couple of brands to choose from. If, on the other hand, you're simply doing small patches and basically painting over the other surface of your wall, you can go with the modern self-priming paints, no problem.
Of course, my favorite to have on hand is ben Primer. This is not water based, it's alcohol based, solvent based, and will not easily clean off of any tools. But, this ben Primer is what you want to use on metal, rust, rusted nails, or anything like that. So, it's good to have this around. So, in summary, go ahead and pick up a gallon of your water based primer if you have a lot of large patches that you want to prime over prior to painting. Otherwise, if you're doing a basic job and adding new color, the self-priming paints are fabulous. You'll have no problem.