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Undercoating
UndercoatsUndercoats or primers are an important step in your painting projects. So what's so special about primer & undercoats, how do they differ from regular paints? Undercoats perform a very special job . . . they are formulated with outstanding adhesion qualities, unlike topcoat paints which are formulated to look good, wear or weather well and maintain color fastness. Some undercoats can even act as a intermediary between a flexible surface and a rigid paint film... expanding and flexing with the surface and brining the rigid film along for the ride.
What Type Should I Use?
New Interior Wallboard or Gyproc
New wallboard need to be sealed to prevent the topcoats from just soaking in to the surface paper. Many people just apply two coats of topcoat rather than using a proper sealer. While this may appear to cover dirt and stains that would wipe off if the surface was properly sealed, end up penetrating the paper making them impossible to remove. If you use an ordinary latex paint as an undercoat the water in the paint will raising the fibers of the paper covering on the wallboard. This would then require the surface to be sanded before the topcoat could be applied. Latex Sealer on the other hand have vinyl resins added that bind the paper covering together and provides gives you a smooth, flat surface ready for your finish coat.
Wood Primers
When painting raw woods, especially cedar and fur be sure to use an exterior alkyd based primer. This primer will stop the natural oils of the wood from coming to the surface and discoloring the finish coat. These primers are only necessary if you are using a latex based paint as your finish coat.
High Hide Primers
When changing colors drastically, from a very dark color to a light color you should be using a shellac based primer. These primers can do in one coat what a regular primer will do in three. They are also used to seal off water damaged wallboard and to seal smoke damaged materials, they will also help to eliminate the odor of smoke or water damaged substrates. This product is also being used for priming melamine laminates.
Glossy Surfaces
If you are painting over a glossy surface always use an alkyd or shellac based primer. Latex based paints and primers will not adhere properly to glossy surfaces. Some high grade acrylic finishes are on the market now and with some light preparation they are working quite well over glossy surfaces.