A recent issue of FHB had a letter from a painter who said there was no need to use oil-based paints anymore, because today’s water-borne (as opposed to water-based) paints perform just as well.
I have never heard of water-borne paint. How is it different from the paint most DIYers use?
We need to replace some molding but it is only available pre-primed, and it doesn’t say what kind of primer was used. I want to use the same paint that was used on the rest of the molding, but that was oil-based and I read that oil-based paint cannot be used over water-based. Any idea what they use to pre-prime molding, and if it is compatible with all paints?
Janet
Replies
I have no technical knowledge about modern paints, but I do know there is an awful lot of flat-out contradictory information floating around out there, so it's frustrating. This past year I built and installed exterior trim around my house and I used Benjamin Moore Fresh Start latex primer (023) under a Japanese oil-based single-component urethane finish paint. It's holding up well at present, but only time will tell. Benjamin Moore states that the Fresh Start primer can be used under any BM finish paint, meaning oil- or water-based, so it's just not true that you can't use oil-based finish paints over water-based primers. All I can figure out is that it's dependent on the specific combination.
Everybody says you can't use oil over latex, but nobody says what will happen. At first I thought that the primer would dissolve, but your experience says otherwise.
Perhaps it matters whether the installation is indoors or outdoors. It's not as though my basecap molding will be subjected to rain or a wide range of temperatures.
Janet
I can't say that I know all of the details, but, in part due to the regulations limiting VOCs in paints, what used to be oil paints now mostly have water as the principle "vehicle". This is not the same as "water based", but rather it's sort of like small amounts of oil have been dispersed in the water in an "emulsion". The effect is to have an essentially "oil" paint with very small amounts of the traditional oil vehicle in it.
"Factory primer" is generally compatible with either "oil" or latex paint (though in general "factory primer" is worthless -- if you feel you need a primer, apply another coat).
by factory primers do you mean off the shelf at HD? ie, kilz and such. And, by the way, do you only prime new construction and patches? Some insist you prime anytime you paint again and the book says it's important for adhesion.
"Factory primer" here means
"Factory primer" here means the stuff that's already painted on the boards (like the yellowish Hardieplank) when you buy it at Home Depot. In addition to Hardieplank, you can also find factory-primed trim boards and such.
How much you prime is relative--up to your personal discretion--but I would prime anything, new or repaint, if I wanted optimum longevity from the paint job.
The company that sells my molding said it is latex primer and I can't use oil-based paint on it. So, I either have to use a different paint and hope it matches the existing molding, or strip off the primer and re-prime with oil-based.
At least I can do the paint removal outdoors, and use a fast-acting stripper. But the task's a bummer. :(
Janet
Concerns with stripping
I think I would be at least as concerned about using chemical strippers as oil over the latex primer. Most fast acting strippers contain waxes to retard the drying of the nasty chemicals that soften the paint. If care is not take to insure that all the wax is removed after the primer is stripped, you can have poor adhesion. Also, sufficient time must be allowed to allow the chemicals and moisture from the stripper and the after stripper wash process to evaporate and not attack the next coat that is applied.
Are you sure that you can't use an oil-based primer over latex? I've done it many times without issues. When I got quotes for my house, it seems that all of the painters use an oil-based primer and then finish with latest topcoat.
Contacted Benjamin Moore
They say that their oil paint is designed to be used over either type of primer--assuming it's a quality primer applied properly.
As for water-borne paints: They have several lines, with "Advance" being closest to oil-based enamel we've used before. The sheen will probably not match exactly, though.
Janet