Glossy surface primers fill an important niche in architectural painting. Sometimes it is all but impossible to sand the substrate well enough to de-gloss the surface adequately for proper adhesion. Other times, as in the case of lead paint, you should not sand the surface in order to de-gloss the substrate.
Question: Can you paint (prime) over a glossy surface without sanding or de-glossing and still get proper adhesion?
Answer: Yes you can. You must use a primer intended for glossy surfaces - known as a bonding primer. You will always get stronger adhesion if you de-gloss by sanding or using a chemical de-glosser. But there are a few primers that are made to adhere to glossy substrates and will adhere to many hard-to-grip substrates, even if you don't dull the surface.
2. If I can't sand (as in the case of lead paint or pre-1978 surfaces and in some other circumstances), I will first clean the substrate very well, then prime with a bonding primer.
Remember: You are always better off if you degloss and prime.
Glossy surface primers (bonding primers)
There are three primers that I use for glossy surfaces without any reservations. They are: Zinsser's B-I-N, Coverstain and XIM's UMA (urethane modified acrylic). There is a fourth, which is XIM's 400 white, but it has settling problems that prohibit me from stocking it on my truck, so I don't use it that much. But, if you buy 400 white fresh (have the paint store shake it well), I think it is probably the very best adhering primer of all the above
The BIG THREE.
Of the three primers mentioned, Shellac primer (B-I-N) is an interior only primer. B-I-N is the fastest drying and adheres to most clean glossy surfaces without sanding. You can test the primer's adhesion by conducting a tape test to be certain (this is the safest way to go about painting glossy surfaces). Of the three, B-I-N is the most brittle, but has the best stain blocking and sealing capability.
Coverstain is an alkyd primer, and is the most user friendly, in terms of being a little bit more forgiving if the surface is not absolutely squeaky clean. Coverstain is probably the one you will have the least problems or surprises with. It is a reliable primer. The hang up with the short oil, quick drying oil primers is that they have very strong odor. You MUST use good ventilation with both B-I-N and Coverstain - especially Coverstain. Coverstain unlike Kilz, is an interior and exterior primer. (I think Coverstain’s odor is a little less strong than that of Kilz).
UMA primer is the best adhering waterbased primer I have used. It really bonds well to clean hard-to-adhere-to, glossy surfaces. BUT it is a latex primer and latex primers are very sensitive to surface contamination. The surface must be absolutely and perfectly clean for a waterbased primer to adhere. Greasy, waxy types of contamination will repel a waterbased paint, just as wax repels the water on a waxed car. The paint will bead up and crawl if the surface is not clean. And, even if it doesn't bead up, it won't wet through a waxy, greasy contaminated surface. So. If you are going to use UMA, be sure to thoroughly clean the surface that you intend to paint. One other note about water-based primers: they dry quickly but cure slowly. It takes about two weeks before UMA will develop full adhesion. Until then, the primer will be a bit soft and may scratch off. Keep that in mind if you are painting a surface that will be subject to handling and wear in the interim..
The surface must be clean
This point is very important. The surface MUST be clean in order for a primer to adhere to a glossy surface. One thing that sanding and chemical de-glossing does (other than dull the surface) is clean or resurface the substrate.
My rules:
1. If I can sand or de-gloss, I will sand or de-gloss first before priming with a bonding primer.
Painting Over Glossy Surfaces
Glossy Surface Primers
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