You can know from your high school chemistry class that oil and water do not mix. Both paints and stains are either oil-based or water-based, and when mixed, the effects can be catastrophic.

More specifically, water-based paints can not adhere to the oil-based product, so they spill or peel. Because the water paints are on the top of the board, the oil-based products are not able to penetrate the wood and never set.

Transparency Test Most oil-based paints are designed to sink into wood. Stains and varnishes can be easily detected by inspecting the surface of the house. If you can see the wood grain and the stain simply color and enhance the wood, it is an oil-based product to be used.

More and more non-transparent stains are being used, however. Such stains often sink into the wood, but they give the appearance of painting by covering all aspects of the surface. For this reason, the transparency test can be trusted to determine transparent oil-based products, but should not be the only method for the determination of solid or semi-transparent paints.

The Goof Off test Since some oil-based paints exhibit the same characteristics as water-based paints, the Goof Off test should be used before any painting is done.

Goof Off and similar products eliminate all kinds of materials, such as grease, markers and latex (water based) paints. Buy a bottle of goof off in your local hardware store. There are other brands available, just make sure it says it eliminates latex paint.

Douse a rag with a little bit of goof off and find an inconspicuous place to test on your wall. Start brushing the wall with the wet part of the rag (wear gloves). If the color starts to come off, it's a water based paint. If the paint is already peeling, make sure you have signs that the mess off is actually breaking down the paint. The paint is going to bubble or look like it's melting or wet.

Converting Oil to Latex You may want to use latex because it's a lot easier to work with. Many older houses have oil-based paint since it was primarily used in the past. If your building is painted with a solid oil-based paint, you will have to use the primer first. The primer will bind to the wall and provide the surface for the latex paint to stick to. When you go to the paint shop, make sure you tell them you're covering a latex paint oil and they're going to make sure you get the right primer.

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