I was called to a jobsite today to look at some crown moulding that we provided (did not install) for a tenant finish project. We provided other millwork and casework on the job as well.
There is a problem with the end to end crown joints pulling apart (see photo). This is occurring all over the building, but does not occur on any base, casing, etc. The base and crown were run from the same lumber.
The GC said it couldn't be anything other than the wood shrinking. I advised him that wood expands/contracts very little along its length, and if there was enough moisture in the wood for the crown to shrink that much, we couldn't have run it through our moulder (it would have had to be green). And if it had shrunk that much along its length, the width would have been much greater (but the width was the same). The species is African mahogany.
We didn't resolve anything, but I could tell the GC (PM and Super) doubted what I was saying. We brought along two references indicating the fact we were stating, but it didn't seem to help.
1. How would you handle the situation?
2. Any ideas on what is causing this joint to open?
The cause is not poor installation. Something has moved, and I'm guessing it is the building, sheetrock, or something else. I am not an expert in those materials, so any help would be appreciated.
To give you an idea on what I'm dealing with, after discussing the crown problem, they had me look at some trim where the "finish was coming off." They scraped the face with their fingernails and something flaked off. At first I was worried and suggested they might have used too much water while wiping the wallpaper paste off our millwork. But, after scraping a little bit more, we saw that the flaking *was* wallpaper paste. When we scraped enough, we got down to the nice shiny finish. They both accepted this problem as theirs!
I'm confident the joint problem is not ours, but proving it to them is another story.
(Architectural Woodworking Forum)
> I advised him that wood expands/contracts very little along its length...
This is true, and we have a Knowledge Base article at WOODWEB that discusses this issue. It can be found at:
I've copied the content at the end of my post... the second sentence of Gene Wengert's answer seems to sum up the relative movement when wood shrinks lengthwise.
My feeling is that it would be unlikely that longitudinal shrinkage was the culprit, particularly since you mentioned the crown was run from the same batch of cherry that the base was run from. If longitudinal shrinkage was the culprit, it would likely also have caused problems with the base. I'm also interested in whether the other joints in the crown opened up. I'd be more inclined to point to building movement as the culprit, but if that were the case, I'd also expect there to be evidence of building movement (i.e. drywall cracks).
I guess the real issue is "How would you handle the situation?" Being right doesn't always translate into being off the hook. I've been in situations where I felt very strongly that the problem was not my fault, but also understood that drawing a line in the sand was not the best way to handle the problem. I think your actions at this point might be influenced by your past/ongoing relationship with the contractor. Do they provide a substantial portion of your annual work? Are they good to work with? If so, working with them to fix the problem might hurt initially, but pay off in the long run. Do they provide little work for you, and are they problematic to work with? This might convince you to take a tougher stand.
Another shrinkage related article at our Knowledge Base that you may want to review:
From "Calculating Longitudinal Shrinkage":
What factor should we use for calculating longitudinal shrinkage in hard maple strip flooring?
I do not have any good ideas other than to use the traditional number of 0.2% (green to dry) which amounts to about 2-1/2 inches per 100 feet. However, since the shrinkage change occurs over a 30% MC change, then we could also say that the wood will shrink longitudinally about 0.1 inches per 1% MC change per 100 feet.
The problem comes when we consider the cross grain in the wood, plus any juvenile wood, all which can shrink up to 30 times more lengthwise. I haven't seen much discussion of this lengthwise shrinkage.
Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.
The wood would not shrink that much (this gap is 1/8") for length. And if it was a moisture issue, the width would have drastically changed, and it is exactly the same as milled (6").
I'm not trying to "pass the buck" in any way. If I was at fault, we would replace it in a heartbeat. There is about 3,000 lineal feet of crown moulding on this job, and I'm not about to replace it when I'm sure we are not at fault. Wood does not move that much in the direction these gaps are appearing. If it had, the material would have been green, and we wouldn't have been able to machine and finish it. The gaps are not appearing throughout the space, either - just in about 1/4 of the joints.
At any rate, were you able to observe the job before the joint opened up? Or can a neutral third party confirm that the joints were tight to begin with?
Also - a thought... by any chance is the ceiling that the crown is installed on fastened to roof trusses? Expansion and contraction of the bottom truss chord is a well-documented phenomenon, and could easily create enough movement to open up a joint.
The walls are metal studs in a commercial building. Concrete floor, and sheetrock both faces. The ceiling is drop-in grid. In my opinion, it is the ceiling that is moving. But I don't know enough about it to know for sure. What I do know is that it is not the wood shrinking for length. The width would have drastically changed, too.
I crunched the numbers. According to the Knowledge Base article above that contains Professor Wengert's comment on longitudinal shrinkage: "then we could also say that the wood will shrink longitudinally about 0.1 inches per 1% MC change per 100 feet."
Let's apply this to your situation. Assuming the length of two pieces of crown that meet is 10 feet (each), his comment above would translate into the crown shrinking 1/100th of an inch (.01) for each percentage change in moisture content. In order for each piece to shrink 1/16th of an inch (one half of the gap), there would have to be a moisture content swing of over 6%.
I used WOODWEB's wood shrinkage calculator
which is for *width* shrinkage, and ran the scenario through the calculator, using 6 inches for the width, mahogany for the species, and a moisture change of 6%.
The result was a predicted shrinkage of 1/16th of an inch in width, a shrinkage amount that would be tough to confirm in the field.
But this triggered what I think is a more important question: are there any examples of two *short* pieces pulling apart, or are the gaps only limited to long runs? If the gaps are limited to long runs only, it seems this weighs in favor of crown shrinkage. If the gaps also occur in short runs, this would seem to me to favor building movement.
Another point I forgot to make is that this mahogany was finished in our shop in the Midwest during the winter (with our shop heaters drying the air out). The material, if anything, would have been much dryer in our shop than in the field (where they have humidity control). If anything, I would expect the material to expand, not contract.
To answer your question concerning material lengths, I didn't catch if this was only occurring on long pieces. What baffles me is that it is happening on a few joints, and not all of them. On a run of crown, two joints might be fine, and the third is spread apart.
> If, in fact, the crown is shrinking that much in length, why not the base that came from the same material?
> And why is it not consistent for all the crown?
> What baffles me is that it is happening on a few joints, and not all of them. On a run of crown, two joints might be fine, and the third is spread apart.
Assuming that the material came from the same run of lumber, and the moisture content was acceptable at the time of delivery, it seems that there are numerous supporting arguments that shrinkage is not the cause.
This seems like a situation where who's right and who's wrong will never be agreed on. I don't envy your position: figuring out a way to get closure on an unresolved problem.
The wallpaper paste story is another "tell" on the folks you are dealing with. Myself, I'd try to get the money I'm owed from them, if any, and tell them to bite me.
I have seen the same thing happen with joints when these rules are not followed. Print this thread out and give it to the owner and GC and see what their response is. Having only supplied this trim in good dry condition, I think the issue would be with the installer and GC. Did they follow the trim specs in the job spec book?
But the big problem is where the finger stops being pointed. I would tell the installer I'll get another length of crown for him and he can install it without each of us charging the builder. This way everyone is happy and it could end up being a good relationship in the long run. Just make sure that they install it the right way the next time.
Why not offer to fill the gaps as good as possible in the meantime, using a soft, pre-tinted, oil base filler?
Comment from contributor X:
Your shrinkage problem might be the building itself and not your molding. In conventional wood framed buildings, the framing is not kiln dried and many times I have seen the walls shrink in thickness and look as though the crown has shrunk. In your case, the length might be affected if the building had long walls that are steel framed, which will move in length.
A lot of ifs, but the only reasonable culprit is the metal expanding wall dimensions. There is no way that the moulding is shrinking along the grain.
Also, I would investigate the anchorage of the molding. Is it anchored to the wall, to the ceiling grid or both? Decide which surface or system is the predominate support and analyze the condition from that aspect. Don't forget the ceiling grid is metal, which is very expansive and so are the metal studs. Depending upon the environment, these systems will move around and take everything attached with it. That is why specifications usually require that the building HVAC system bring the building temperture and humidity to a normal operating level at least a week in advance of hanging any gyp board and other materials. So check the specs and ask to see the daily log (if available, or check with the local weather bureau for a history) to get an idea about the conditions in which it might have been installed. Finally, did the contractor run auxiliary heating units to dry out the building quicker during the drywall installation and finishing process? This would throw an unusual amount of heat at the ceiling, making things move around, if nothing else.
I have run into this many times. One bank called up about the cracks in the crown molding (miter, glue and pinned) and they still separated. We puttied the cracks, applied another coat of finish and then got called back in the spring when putty was pushed out of the cracks.
The building and the trim must be climatized before any installation can begin, otherwise no warranty can be given. How much water is in a 5 gallon bucket of sheetrock mud? How many fives applied in the building? All that moisture does not go strictly to the surface. Was the rock delivered in the rain? Was it stacked on the second and third floor before the roof was completed and windows in, and then hung later? Many commercial buildings will not turn on the heat and/or air until the rock is sanded in order to save the units from the dust.
And you are always asked to install just as the drywall sanders are through. We are always installing when they are still hanging on the next floor. "We have to get the job finished. If you don't do it we will get someone else." I simply send a certified letter to the general contractor stating that all warrranties are void if we are told to proceed in an unclimatized building (as stated in the specifications and contract documents). No one worries about the letter. They tell you to go ahead and put it up, but when warranty issues come up, that $3.25 and five minutes of your time answers all the questions! And nine times out of ten, they will pay you to repair the problem.