Using old oil paint as primer
I bought some oil-based paint a few years ago and never used it. Now, having sandblasted my siding, I’d like to use an all-acrylic paint instead because it’s supposed to last longer and resist fading. Because I need to use an oil-based primer for the acrylic paint, will my original oil-based paint suffice as the primer if it is thinned? If I can’t use the oil-based paint as a primer, what should I do with my 12 gal. of yellow oil-based paint?
Toney Palakewitz, Salem, CT
Victor DeMasi, a painter in Redding, Connecticut, replies: There are many kinds of oil-based paints on the market, and their uses vary tremendously. An oil-based primer-sealer made specifically to be used under latex finish paint is a good choice for a sandblasted house. If your house is typical of most houses in New England, the siding is probably either pine or cedar.
These resinous softwoods tend to bleed, which can ruin the appearance of the finish coat of paint. A coat of primer that is also a sealer will prevent bleeding, and I know of only oil-based products that perform both functions. Sandblasted wood is extremely porous, so figure on extra quantities of primer, and allow ample time for drying before applying your latex finish. Sandblasted surfaces often require two coats of primer with sanding between the primer coats.
Old-timers would often thin an oil-based finish paint to use as a primer. But paints back then were different from today’s products, and acrylic latex didn’t exist. Acrylic paints tend to adhere poorly to oilbased finish paints, especially gloss paints. Unfortunately, the 12 gal. of paint you bought originally are probably oil-based finish paint with a glossy finish. I recommend discarding it in an environmentally safe manner (ask local officials about hazardous-waste collection days). The value of the labor you are gambling with by thinning the paint and using it as a primer far surpasses the value of the paint. Thinned oil-based paints should be used as primer only on hardwood species of lumber for interior work and only when an oil-based paint finish is to follow.
I’ve painted hundreds of houses with a universal oil primer followed by two finish coats of high-quality acrylic latex house paint, and I’ve had excellent results. Even after ten years, many of these houses need only minor surface prep and a complete washing before they’re repainted.