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post #1 of 19 Old 01-07-2013, 06:48 PM Thread Starter
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problem with crown moulding

i put up some crown moulding (mdf) in my parents house a year ago. when i finished everything looked great, now a year later my joints are opening, cracking and the chaulk is seperating from the ceiling. i mitered and glued all joints. can someone tell me why this is happening, and how to prevent this in the future.
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post #2 of 19 Old 01-07-2013, 07:21 PM
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This might be appropriate. Hard to say other than improper installation, or house settling. MDF mouding doesn't expand or contract.





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post #3 of 19 Old 01-12-2013, 12:33 PM
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MDF DOES move. In my experience you have to use a really good glue for your outside miters. Did you cope the inside corners?
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post #4 of 19 Old 01-12-2013, 11:24 PM
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Quote:
Originally Posted by cfullen View Post
MDF DOES move. In my experience you have to use a really good glue for your outside miters. Did you cope the inside corners?

REALLY... In 40+ years I've NEVER seen MDF "Move". Now it will swell like
crazy if it gets wet but if sealed properly it will not "Move" laterally. Just can't happen due to the nature of it's construction.

Still Got ALL my Fingers!!!
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post #5 of 19 Old 01-12-2013, 11:39 PM
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Quote:
Originally Posted by MissionIsMyMission View Post
REALLY... In 40+ years I've NEVER seen MDF "Move". Now it will swell like
crazy if it gets wet but if sealed properly it will not "Move" laterally. Just can't happen due to the nature of it's construction.
+1. I used the words "improper installation", which may also account for a poor paint job, and/or lack of good glue joints. Most likely it's glued to other MDF, so the joints are all the same material. It can swell, but in most residential or commercial settings the ambient moisture levels don't vary much. If "swelling" does occur, it's most likely that the moulding isn't sealed enough. I've never seen it happen either.




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post #6 of 19 Old 01-13-2013, 12:33 AM
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Might not be the crown molding that is moving. Is it a truss roof frame? A common problem with wood truss roof framing is "truss lift" which is more pronounced toward the middle of the building (center of the truss) and less so near the outside walls or bearing walls. It will look like the walls are settling away from the ceiling but it's actually the ceiling lift away from the walls, and the molding which is typically nailed to the walls, gets left behind with the wall.

We learned how to deal with this problem with some framing and drywall installation techniques. If interested I can explain in detail.

Bret
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post #7 of 19 Old 01-13-2013, 07:55 AM
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The biggest problem I've had with MDF molding is the nail gun shooting the nails almost through the trim so later it just pulls off the nails. This may explain it pulling from the ceiling but the ends sounds like the house settling.
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post #8 of 19 Old 01-13-2013, 09:28 AM
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I live in one of the most humid climates in the US. I have seen inside corners that were snapped in tight as a nuns butt open up.
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post #9 of 19 Old 01-13-2013, 09:34 AM
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Mitered inside corners are notorious for opening up.
This is why we cope.

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post #10 of 19 Old 01-13-2013, 09:40 AM
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You can't always cope crown. The big mdf is too thin and too intricate.
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post #11 of 19 Old 01-13-2013, 09:15 PM
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Originally Posted by cfullen View Post
You can't always cope crown. The big mdf is too thin and too intricate.
Sorry CAN'T isn't in my vocabulary.
What's your reason for not being able to??
How large is the crown?

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post #12 of 19 Old 01-14-2013, 10:02 AM
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We hand a wide range of crown sizes. And yes it is possible to cope. It is very tricky though. It makes much more sense for us to use inside miters. Believe me, I cope whenever possible
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post #13 of 19 Old 01-14-2013, 11:24 AM
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Quote:
Originally Posted by Steve Neul View Post
The biggest problem I've had with MDF molding is the nail gun shooting the nails almost through the trim so later it just pulls off the nails. This may explain it pulling from the ceiling but the ends sounds like the house settling.
+1. i always use hand drives when hanging anything but wood crown, i've had it pull through way too often. try to nail into the wall studs and ceiling joists/nailers. remember, gravity will work against it 24/7 - forever.

Last edited by TimPa; 01-16-2013 at 07:04 AM.
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post #14 of 19 Old 01-15-2013, 08:27 PM
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I'm doing finish work in a house that had extensive reno done. Complete new roof stick framed. The ceiling joist rose up in the master bath and now there is almost an inch gap in drywall around the inside part of the room, maybe something similar happened w/your ceiling/walls.
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post #15 of 19 Old 01-21-2013, 09:43 PM Thread Starter
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thanks for the responses. i did some research last week and found through some building association (cant remember where now) but it said that a 16' piece of mdf can shrink up to 7/16", and wood same size can shrink up to 3/32". that has to be under super extreme conditions. house is 35-40 years old. most inside miters and some scraf joints are opening, all were glued and nailed to both wall studs and cieling joists. any outside corners still look fine. i am hoping that using wood and coping will eliminate the problem.
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post #16 of 19 Old 01-22-2013, 08:52 AM
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What size crown are you using?
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post #17 of 19 Old 02-20-2013, 11:27 PM
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Backer block at each joint. Construction adhesive at the blocks. Lots of yellow glue and stitch nail.
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post #18 of 19 Old 02-21-2013, 06:54 PM
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Arrow

Always cope and snap your miters,,,,,, openings will more than likely be non existent thought the life of the trim.



It's a little more work, but it is not that bad once you get in the habit of working your ISC's with a cope joint......


JMPOV,



B,
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post #19 of 19 Old 02-25-2013, 07:34 AM
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Quote:
Originally Posted by Nittany Nation View Post
i put up some crown moulding (mdf) in my parents house a year ago. when i finished everything looked great, now a year later my joints are opening, cracking and the chaulk is seperating from the ceiling. i mitered and glued all joints. can someone tell me why this is happening, and how to prevent this in the future.
The same exact thing is happening in my house. Worse towards the center of the house. Exterior walls havent budged but all the interior walls have separated from the ceilings...and it is only on non-bearing walls I might add. It is not noticeable where I did not caulk but everywhere I caulked on an interior wall it has separated from the ceiling.

I asked my dad (who has been doing this stuff for over 50 years) he said it was the trusses in the ceiling (we have a ranch home) "lifting".

He gave me two tips;
cut out the caulk and replace it with a caulk that expands and contracts with movement like window caulk does

or

dont caulk the ceiling portion of my crown molding.
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