Paint which surfaces of indoor built-in bookcases?

I learned from my first outdoor project that plywood doors painted on one side will warp when it rains.
But what about indoor bookcases in a climate where the humidity is moderate most of the time (SF Bay Area)? This installation is three built-in bays, sitting on a base and screwed to a wood wall. The outside surfaces and edges of the boxes will be hidden by trim. I don't want to paint more than I have to but I don't want warped cases in a few years.
Thanks in advance for advice.
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wrote:

Finishing all sides will help reduce the chance of warp. Allow the paint to cure for 4-6 weeks before loading it with books.
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You already know the right answer. So you want our blessings to take the lazy way out.
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And with a foam roller, you'll be done in no time. Since it won't show, you don't have to use your fussy work. You only need to sand to 120 grit.
Use the good primer, though.
Patriarch
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wrote:

Paint everything and for goodness sake, don't use latex paint, unless you want to have books permanently glued in position.
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Thanks all for the advice. I will paint everything that isn't glued.
By the way, I talked to my local paint store about latex and sticking books. They said that Benjamen Moore _exterior_ latex will work fine, but it needs 30 days to fully cure. It may be different with other brands.
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Bill Courington wrote:

I try to paint/varnish when the air is dry or dry-ish but as much as I like painting some things I've gotten into the habit of using polyacrylic over acrylic. (I write acrylic because I think very few paints are still latex. Most if not all paints are now acrylic or acrylic-latex.) Anyway, a couple of coats of polyacrylic over paint gives you look of paint with the protection and good attributes of polyacrylic.
Josie
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I asked Jeff Jewitt that question regarding a chest I was making. Did I have to use the same finish inside as outside. I was using a hybrid Target varnish on the outside but wanted something odorless (shellac) for the inside. He said no problem. He said the only time he worries about finishing both sides of a unit the same is when the piece receives minimum support such as a table leaf. JG
Bill Courington wrote:

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By all means shellac the outsides and backs. Won't hurt, might help. Zinsser makes shellac primer.
However, the realist in me says books are more likely to have their way with wood than moisture.
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