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A few years ago I had a handyman replace a few rotten siding boards with cedar. He recommended that I wait a couple months before painting the boards. I don't recall his reasoning, but I remember he talked about how when my home was built (the 80s) they didn't put a layer of plastic sheeting (or something) behind the siding like they do on modern homes, because they found the (resins?) from siding would degrade it and they hadn't yet come up with the technique of "back priming" to solve the problem. So my impression was he thought there may be some negative chemical interaction with the paint.

I have to replace some more siding. I have the boards and my plan is to prepaint them before installation. After doing some research, I've found several sources that recommend the opposite of what the handyman said, for instance:

For best results, fresh siding should be pre-primed on all six sides with a stain-blocking primer and top coated with 100-percent acrylic-latex paint. Alkyd-oil primers are recommended, but one may choose a high-quality latex primer as long as it contains stain blockers....

It is recommended that you paint within two weeks of installing the cedar. Make sure that you wait no more than 12 weeks.

Allowing fresh siding to weather for as little as two weeks negatively affects coating adhesion. Test results from the Forest Products Testing Lab (run by the USDA for the Forest Service), show that after 12 weeks of exposure to sunlight, cedar siding has lost half of its ability to hold a film-forming coating system like primer and paint. Another test at an experimental facility in Madison, Wisconsin involved a sample section of red cedar siding that was pre-primed on all six sides (including the ends), top coated with two coats of paint, and placed in a frame. The test section has never been re-coated and it shows no degradation of the coating system, though the test is over 25 years old.

Other samples were allowed to weather for three months, six months, nine months, and 12 months before being primed and painted. The longer the siding was allowed to weather, the sooner the coating system failed. And in all of those cases, it failed to start at the end grain where the siding abutted trim because the ends of the siding had not been primed. [Source]

I have two questions:

  1. When should I paint? I'm leaning towards painting early because the results of the Forest Products Testing Lab are compelling.

  2. What was the handyman thinking? Was waiting to paint cedar an old practice that became obsolete, maybe because of improvements in paint technology?

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In my region (pacific north west), weathered cedar is not painted at all, or just painted on the outside, with no priming or other conditioning.

It's possible that fresh cedar, or cedar in other climates is treated differently.

Cedar siding and fences here are sometimes treated immediately for extra longevity or to apply a stain for aesthetics.

I would check with your local cedar supplier (not just the stain supplier) to determine best practices for your region based on the type of cedar and probably also its moisture content.

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