This will lay a first layer of velcro-like surface on which the paint will stick. Then, add oil bond directly to your paint using a clean bucket. One bottle of oil bond treats two gallons of latex based paint. polyurethane can be oil- or water-based, and you can use either kind over latex paint however, oil-based polyurethane tends to yellow as it ages, whereas water-based varieties stay transparent. Oil-based varnishes are formed from mixtures of oil and resin, and cure by evaporation. They dry slowly, and are often used as an alternative to lacquer, which is somewhat dangerous and often not suitable for an amateur or hobbyist. bear in mind that exterior oil-based or marine spar varnishes have a tendency to yellow over time and will change the paint color. Virtually any type of varnish will work over latex paint except lacquer. Oil-based varnishes and polyurethanes can be used over latex paints. virtually any type of varnish will work over latex paint except lacquer. Water-based acrylic varnish also can be used over any type of latex paint. It is thinner than either oil or polyurethane, and may take an extra coat to achieve full hardness and shine. Those are the three best ways to transition oil based paint to latex in order from easiest to hardest. The age and hardness of the paint will determine which will be the most effective for you. Remember to always do a test spot first! Call paragon painting. Oil-based varnish, including polyurethane varnish and oil paint, can also be sprayed, of course, because any thin liquid can be sprayed. Varnish dries much slower than the other finishes, and unlike lacquer, shellac and water-based finish, each coat should be allowed to fully dry before the next coat is sprayed. If youre dealing with an older painted surface, the paint is often oil-based. To determine whether the paint is oil-based, test it by rubbing a small area with a cotton swab dipped in alcohol. If the paint rubs off, its likely oil-based and requires a water-based primer before applying varnish. Some latex paints contain low concentrations of ethylene glycol (anti-freeze). Ingestion of very large amounts of these paints can cause gastrointestinal upset, neurologic signs and even kidney failure. Oil-based paints and varnishes contain solvents that can be inhaled into the lungs and cause difficulty breathing.