Mitered joints in casings opening up - what to do?

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Forum topic by isotope posted 01-25-2016 04:03 PM 530 views 0 times favorited 9 replies Add to Favorites Watch
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144 posts in 1044 days

01-25-2016 04:03 PM

Topic tags/keywords: casings trim mitered joints question

I have been rehabing our old house for the last couple years. During the course of this work, I have replaced almost all of the trim, including door and widow casings. None of the mitered joints are perfect, but I’ve improved as I have done more of these and changed my methods. The most recent ones, I assembled the casings, using glue and pocket screws (from behind) and then nailed the assembled arch to the wall. This has proved to be the best method for me so far. However, when I first started, I would nail the pieces to wall, separately, and fill the gaps with wood filler. This looked fine at first, but during the winter the mitered joints open up. These casings are finger jointed pine.

My question to you all is: what should I do now? I’m not obssesd by it, and can live with it if there isn’t a good solution. But, I hoping someone has a relatively easy fix.

Thanks in advance for all the help and ideas.

9 replies so far

View conifur's profile


955 posts in 571 days

#1 posted 01-25-2016 04:14 PM

Recaulk, and get a humidifier.

-- Knowledge and experience equals Wisdom, Michael Frankowski

View jbay's profile


700 posts in 319 days

#2 posted 01-25-2016 04:17 PM

Take the trim off and rebuild the door opening making it smaller at the bottom. When you reapply the trim the joints will close. You will also have to trim the door at an angle.
If that’s too much work, then just caulk it and repaint. :)

-- Many times my “MO” involves Judging others, playing God, acting as LJs law enforcement, and never admitting any of my ideas could possibly wrong or anyone else's idea could possibly be correct.--

View isotope's profile


144 posts in 1044 days

#3 posted 01-25-2016 04:20 PM

Take the trim off and rebuild the door opening making it smaller at the bottom. When you reapply the trim the joints will close. You will also have to trim the door at an angle.
If that s too much work, then just caulk it and repaint. :)

- jbay

This seems like a great idea! ;)

Will the caulking be flexible enough to expand and contract with the seasonal movements? Or will get squeezed out when the summer comes?

View hotbyte's profile


825 posts in 2395 days

#4 posted 01-25-2016 04:22 PM

Call it character :)

View OSU55's profile


1039 posts in 1409 days

#5 posted 01-25-2016 04:26 PM

Do you use o humidifier to maintain moisture levels in the house during winter? This will help the house and the people in it, as well as make a given temp feel warmer. You can get a % RH / temp meter cheaply at the bbs. I try to maintain mine at 40% min, its usually in the mid 40’s. Keeps moisture in all the wood maintainings door and window weather seals. Its not just the trim moving but also what it is attached to. I’ve had good luck with flexible non shrinking paintable sealant in an app like yours.

View splintergroup's profile


723 posts in 642 days

#6 posted 01-25-2016 04:35 PM

A number of things could be causing it (casing movement, door frame movement, etc.).

What I do is spline the miters so there is no way they can separate. After this, it just comes down to a mounting method that allows for movement.

Typically I’ll avoid any fasteners between the casing assembly and door frame that are within 6” of the miters. This allows the casing to bend a tad without breaking the miter.

My splines are really a form of lap joint. I cut away about 1/4” from the rear of each piece and then glue in a ‘spline’ that laps into the cuts. The spline grain direction is perpendicular to the miter for maximum strength.

One could just do a half lap with the two trim pieces, but I found that doing the spline on the back to be easiest since the front of the trim is rarely flat 8^)

Your glue/pocket screws method should be fairly ridged, perhaps just keep the nails about 6” away from the miter and see if that cures it?

View isotope's profile


144 posts in 1044 days

#7 posted 01-25-2016 04:54 PM

No, we don’t currently run a humidifier. It’s a good point and something we should probably do for comfort purposes.

At some point, I had the idea of using my biscuit jointer to reinforce the mitered joint. But due to the profile, there isn’t enough wood in the center of the casing. This led me to pocket hole screws, on the edges of the casings. Another option I considered was bowties (or dutchman), though wasn’t knowledgable enough to know how to pull that one off.

Leaving some space for flexing and wood movement is a good idea. I’ll be sure to do this in the next ones I do.

View runswithscissors's profile


2127 posts in 1444 days

#8 posted 01-26-2016 02:12 AM

When I was putting in trim in a condo, where nothing was square, vertical, or horizontal, the painter showed me his tube of painter’s caulk and told me not to worry about it.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View rwe2156's profile


2114 posts in 900 days

#9 posted 01-26-2016 03:04 PM

Please don’t use caulking. It will shrink, discolor and look awful in a few months.

Not real thrilled with fillers either.

I would run a saw blade to even out the crack and then inject epoxy and put a nail through miter from top to draw together. Wipe off squeeze out immediately any gaps will be filled with epoxy.

You could also clamp from side to side there will be enough flex to draw it together the diff in reveal won’t be that noticeable.

-- Everything is a prototype thats why its one of a kind!!

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