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I replaced the bottom trim on a customer’s porch post last year. Over the winter all the miters opened up. (I can’t get the site to accept a picture) I guess it’s because of the cross grain situation where the post’s vertical grain expands and the trim’s horizontal grain doesn’t. But what can I do to make this trim stay intact and sealed against moisture? It seems plastic trim would have the same effect. <!—->
Any suggestions??
Rocky <!—->
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Replies
This may look like ****, but I was wondering if you could cut the trim at a 45 angle back--so the two meeting at the corner of the post produce a sort of flat facet that is at 45 degrees from faces of the post, plan view like so:
_V_/ (imagine the "V" (post) being more open with a ninety degree angle).
The other idea would be to use decoarative plinth blocks and butt the trim ends into them at the corners (or even inlet the trip slightly into the blocks). I don't know how to draw pictures here, so I can't help much with a visual.
Just thoughts--I'm not exactly a finish carpenter (though I sometimes play one as a job).
One trick is to bisquit or spline the miter joints and apply an exterior glue. To relieve expansion/contraction (as needed), use a scarf joint along the run. Scarf joint is less visible than an open miter joint.
rocky... i avoid miters on exterior trim like the plague...
i think the wood we get today is too juvenile and unstable .. i always try to use a butt joint with the hollywood side to the viewer..
which is worse ? a butt joint or an open miter ?
if you are using composites i'd consider it.. but if it's mdf.. you have to seal the ends before you marry them...
drive around an look at exterior trim on other projects.... 90% use miters.. and 90% of those are open and crooked
Polyurethane glue with biscuits will hold up very well, if requiring some scraping after the glue dries. A scarf joint down the run will keep the vertical post or stile from buckling the horizontal rail too much. Insure that all of your exterior trim is backprimed and endprimed prior to install. Trim with an unprimed backside allows water vapor to enter the wood and exascerbate movement that otherwise wouldn't be objectionable.