Ken Collier: Primers are one of the secret weapons of pro painters and they can help you get great results when you're painting inside of your house.
My name is Ken Collier and I'm the Editor-in-Chief of The Family Handyman magazine. The leading brand for do it yourselfers. One of the best uses for primers is when you have to paint over bare wood, here is the problem with painting over bare wood; let me show you a sample of this pot. Wood has grain and the different parts of a grain absorb the paint in different ways, there are softer parts and harder parts and the softer parts tend to suck up the paint.
When you put a primer on, it soaks in, hardens, and creates a uniformed base layer for whatever kind of top coat you're going to put on. If you don't use the primer, the grain has a way of showing through the final coats, no matter what you do a process called telegraph.
So let's talk about one of the common situations you'll face with bare wood and that is painting clear pine trim, you can use a general-purpose premium latex primer, this will give you a good base for your trim paint. If you're using a glossy enamel, you could also use a latex under coater. .
Another situation you may face is painting over knotty pine, for example with this knotty pine wainscoting. The problem with knotty pine is the knots which have sap in them and various chemicals which will bleed through a typical latex paint. For this situation, you want to use an oil-based prime that'll seal up the chemicals in the sap and make it so your topcoat looks beautiful.
To apply oil-based primer, you should use a natural bristle brush or a good roller and you're going to have to clean up, when you're all done using mineral spirits. Generally you can recoat in an hour, but be sure to check the label, follow the directions on the can of primer that you're using. So that's what you need to know about priming bare wood when you're painting.