Painting surfaces that aren't exposed

Stan in Oly, WA

Well-known Member
I've been finishing up a couple of projects, including adding exterior trim to a tool shed. The trim on the shed is 1x3 and 1x4 pine. Because some inadequately prepped painting on the property didn't hold up very long, I'm being much more diligent about this. I'm priming all bare wood with oil based exterior primer before covering with a compatible water based exterior paint. There isn't a lot of trim on this small building, so it wouldn't take me a much extra time to overdo it if that would make a difference. Would there be any benefit to priming, or priming and painting, the surfaces of the trim that won't be exposed to the weather? I'm not thinking in terms of deterioration so much as warping and checking.

Stan
 

If it is outdoors, eventually it will be exposed. Painting all the surfaces before assembly is probably not a bad idea.
 
I know that some manufacturers say that it's OK to put water-based paint over SOME oil-based products, but I urge you to take a step back and doublecheck that before you start. Would hate to see you go to all that work only for the paint to not bond well.
 
For the last 15 or so years the instructions that are stapled to the end of new beveled wood siding say to prime/paint all sides before installing.
I think it should last longer before needing to repaint.
 
Thanks, that's a good point. I bought the primer with compatibility with the paint already in mind. Actually, water based primer wouldn't have been a bad choice for all the things I've primed and painted (or repainted) this summer because everything was rough enough that raising the grain wouldn't have mattered. It's largely that I'm old enough, as well as old-fashioned enough, that I still view oil based products as providing a more durable finish than water based.
 
Yes, painting it should help.

I also like to run a bead of caulk, like the Alex 230, under the top edge and down the vertical edges before nailing the board on, then caulk again once attached. But, leave the bottom open so trapped water can get out if it gets in.

And try to avoid any exposed end grain on horizontal surfaces. If unavoidable, bevel the end so water will drain away.
 
Really on wood the only reason you use primer is it's thicker and covers better. The paint is what provides the protection. It will need at least paint on the areas not exposed to the weather because wood will warp if humidity can get to one side and not the other. It takes a long time but even humidity alone can rot wood so it needs to be sealed.
 
Interesting. All the primer I've seen for wood has always been rather thin. Always thought it was so it could more easily soak into the wood and cover every divot. ...But then I hate painting. Leave that for the wife! :lol:
 
Repainted our house trim with latex paint over well weathered oil based paint. Only lasted a few short years before latex was peeling off all over the place.

Painted a very weathered barn with latex. Went on like whitewash and came off almost as fast. (think it froze in vendor's warehouse)

Both barn and house now have vinyl siding and aluminum trim covering all exposed wood surfaces. Hopefully I won't have to mess with that foolishness again in my lifetime.
 
You should never put latex paint directly over any oil based paint either inside or outside. To make the transition you should first use an oil based primer to make the adhesion. The barn if the wood was weathered it would have helped to power wash it before painting.
 
Priming or painting end grain is always a good idea, as it is to paint the edges of any plywood. It's not so important to paint the faces of boards, and of course excess paint can keep trim from fitting.
 

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