It might seem tempting to just paint over older finishes. But gloss, dirt and contaminants on the old surface will prevent new paint from sticking. The old finish should be buffed up, roughed up, sanded or treated. If you're thinking about painting cabinets, molding, trim or woodworking, you have two choices for surface preparation: sanding or deglossing.
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Time and Effort
Sanding takes time. You could spend all day sanding just to prepare a previously painted or lacquered finish for new paint. Even with an orbital sander, it could take hours to sand everything, including doors and drawers on cabinets or miles of moldings. Deglossing is faster than sanding. It takes time as well, but it's applied with a soft cloth in manageable sections that speed up the process. The process is mostly wiping everything down and allowing it to work its magic while drying for 30 minutes.
Deglosser Chemical Concerns
Deglosser, sometimes referred to as liquid sandpaper, contains chemicals. Depending on manufacturer, it contains solvents such as naphtha, isopropanol, mineral spirits, ethyl acetate and toluene. Breathing protection, chemical-resistant gloves and eye protection are required when using deglosser. Another product sometimes stocked on shelves along with deglosser shouldn't be confused with deglosser; trisodium phosphate is a cleaner and won't work as a deglosser. If you want to avoid chemicals, deglosser is not your best choice.
Potential Dust and Lead From Sanding
Sanding also has its health issues. Sanding produces dust. You'll need to protect yourself against airborne dust by using breathing and eye protection. Sanding also raises the issue of lead exposure: Oil-based paint made and applied prior to 1979 might contain lead, and precautions should be taken before it can be sanded. If you're not sure, a sample of the paint can be tested. If it's determined that it does contain lead, seek the help of a professional to remove it.
Not all finishes are created equal. High-dollar paints and finishes with ultraviolet-cured coatings, pre-catalyzed lacquers, some varnishes or oil-based polyurethanes will resist deglossers. It's nearly impossible to dull some of these finishes without sanding them. If you don't see results with deglosser, it may be necessary to sand them anyway. If you have questions, test the deglosser on the back of a door or in an inconspicuous location.
Deglosser focuses on dulling an old finish. If the older finish is irregular, rough, pitted or scratched, deglosser won't smooth it. Only sandpaper can repair bad surfaces, smoothing them with its abrasive qualities. If your previous finish needs smoothing in any way, sanding is the only way to accomplish it. If it's rough starting out, deglosser will only leave it rough.