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I read that question in an issue of Fine Homebuilding...anyways..my question regards priming or back priming of high quality trim, baseboards, crown etc. One pro said he had no problem with seasonal joint movement when he primed the heck out of trim with a quality, oil-based primer. I am a newbie here, so should I let my trim pieces acclimate to the room (how long) and will priming my trim pieces "capture" moisture?? Finally, how should one deal with high quality stain grade trim to avoid seasonal movement...thanks all
 

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I rarely have the luxury to allow trim to acclimate in a customers home. They want instant gratification, even when I warn them.

If I have the luxury I like to have it sitting rough cut for a couple weeks in a temp controlled room. I'm no painter but I often prime my trim before install, I leave it up to the customer to putty and paint or whoever they hire to do it.
 

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In my opinion, it depends on your region and how extreme you are with the heat/ac in your house. I installed all new poplar and pine trim in my entire house five years ago (crown, casings, baseboard), and nothing has visibly moved. In the winter my house is never over 68 degrees, and in the summer it's usually around 73-75 with very little ac use. I've never back primed, but a good fit helps too.
 

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If the trim is a natural finish with a film finish, I'll go ahead and shoot the back just to get it covered. Some trim if just sprayed on the face may leave return shapes (on the outer edges) towards the back bare from finish. Spraying the backside insures all visible wood is covered.

If it's a painted trim, the same applies. Having the backside primed or finished isn't really a question of preventing expansion/contraction as that isn't an issue for longrain. Most trim isn't thick enough or wide enough to have crossgrain movement an issue.






 

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This is related to Exterior priming and painting done on 100 plus yr old structures.
Take it for what its worth.
I have 2 houses and 1 Inn over 100 yrs old that I work on, all of them have most of their original exterior trim on them. Some of the trim that isn't original was replaced by me over the last 10 plus yrs.
The rest of the non original trim replaced by other contractors was done in pine and is already in a state of severe rot.

All 3 buildings are within 1 mile from the ocean, 2 of them are on it. Woods Hole, Cape Cod MA., the place is hammered by wind rain salt water, baked by the sun and covered in snow. Both structures are on a slope rising up from the ocean. When the air is calm at sea level it is 20 + MPH on the roof of the house about 100+ feet above sea level and 50+ MPH on the roof of the Inn which is another 130+ feet above the house.

All the original Ext. trim is fir, (I've also replaced with fir) even though I primed the back of the replacement trim none of what I've replaced was back primed or painted. As far as I can figure the type of material, maintenance and the direction it faces makes the difference.

From what I can remember as was suggested to me by more than one ancient, (including late grandfather, who cut, milled and built his own farm house and barns) was once the material was, correctly set in place there was'nt any way for physical contact with water. So any moisture absorbed on the surface had an easy way out via the non primed and painted back.




 

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I have trimmed in Oregon and New Mexico and never have I primed the back and never had a problem. I would spend your time installing it properly and not on priming. Improper installation is going to be your nightmare in the long run. Get a good clean miter on your joints and secure them well. I let most of my wood acclimate at least a week when possible.
 

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I have never used priming but after read it. I will prefer it because it is really better than Plywood. It is very effective and reliable compare to plywood. So, definitely I prefer it.
 
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