Before you begin that painting job, there is one very big decision you need to make. Do you go with oil-based paint, or with water-based paint? How will you know which is the better choice? Which paint should you use when painting over a surface that has already been painted? Which is best for painting exterior surfaces? Which is best for painting interior surfaces?
Water-based paint definitely has some advantages over oil-based paint. For one thing, water-based paint is quicker to dry than oil-based paint. Another advantage to water-based paint is that it won’t show stroke marks as distinctly. In addition, it is easier to clean off than oil-based paint. For many people, of course, the biggest advantage of water-based paint is that it doesn’t permeate the room with the strong smell that oil-based paint does.
On the other hand, if the exterior surface over which you plan to paint was previously painted with oil-based paint, you should go ahead and repaint with the same kind. The problem is that latex-based paints is more susceptible to the expanding and contracting that climate changes cause than water-based paint and therefore if you use a water-based paint to cover an oil-based paint you are running the risk of the undercoating peeling beneath your shiny new paint job. If you are planning to paint an exterior surface that hasn’t yet been painted, go with latex exterior paint. In this way the surface will be better able to breathe. In addition, the latex exerior paint will adhere better during climate extremes.
Before you being painting over an exterior surface that has already been painted, use a piece of sandpaper or a wire brush on it. This will roughen up the shiny gloss enough to allow the new coat to bond better to the surface. Also be sure to heartily clean under any eaves or in any other protected and hard to get to spots. The best method for this cleaning is to use a mixture of water and detergent. Why is this step necessary? Because these areas don’t get completely clean from rain water and if they surface isn’t completely clean, the paint wont bond
You should always use latex paint for indoor surfaces. This is true even when covering up a surface previously painted with oil-based paint. The only exception to this rule would be if the surface beneath the oil-based paint is water-soluble, since the water used in latex paint can lead to a softening of the surface, which in turn could lead to peeling. Using multiple coats of oil-based paint can usually protect the surface, but before you go ahead and take the risk, first do a test in which you paint a small area with the latex paint. Wait a couple of hours and if there is no peeling, you should be okay to go ahead with the full job.
When using latex paint, also be sure to test for whether the chalk from the previous paint job has been removed. To do this, paint a smaller area of the surface just as in the test above, only this time use two coats. And instead of waiting a few hours, you’ll have to wait a couple of days. After two or three days use a paperclip to scratch a line through the paint, then stick some clear tape over the line and quickly remove it. Check the tape for paint specks. If more than a handful of paint specks are stuck to the tape, that means the paint isn’t bonding strongly. This means you’re going to need to do either one of two things. You’ll have to make sure you thoroughly clean off the chalked paint. Or you’ll need to switch to an alkyd paint. Alkyd paints do a better job of covering up chalk.