You will need to wash the varnished plywood thoroughly
as well as sand it to make a "tooth" so that the paint will
The unstated problem here is how the varnish will react
to the paint. If you are lucky there may be no reaction
i.e. the varnish will serve as a primer. If they are chemically
incompatible you will need to remove the varnish.
The borgs can be great. I recently asked one of their paint guys about
the difference between the three versions of Kilz they stocked.
"Doesn't matter. All primers are nothing but elmers glue anyway. They
all use that stuff and put it in different cans."
He claimed to have been a professional painter for fifteen years before
he went to work for Lowes.
I immediately left and went to a real paint store.
A little hard to advise on what little information you've given us, but
The problem you need to solve is the age-old one of "how do I get paint
to stick to this surface?" A couple of aspects of that problem: 1)
problems with adhesion when painting over any glossy surface (either
varnish or paint), and 2) the opposite, the fact that paint sticks
better to roughened surfaces (which you seem to sense in your question
Is the varnish glossy, or satin or dull? If glossy, then you definitely
need to prepare the surface before painting, either by physically
scuffing with sandpaper, or chemically with a deglossing agent. Which
you use depends on information we don't have, such as how large the
cabinet is, what kind of trim it has, etc.
If the surface is not glossy, you can probably apply primer directly
But in any case, yes, you should use primer. My preference is a good
oil-based one, which will stick better than a water-based (latex or
"Wikipedia ... it reminds me ... of dogs barking idiotically through
endless nights. It is so bad that a sort of grandeur creeps into it.
If you want to do it the right way (meaning that you actually want the
paint to stick) I'd sand AND use a primer. If your intent is to use
oil based products check the existing varnish to see if it's oil based
(it probably is if it's a factory coating). If what's already on
there is water based, then use water based primer and paint.
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