Shadow Lines On Cabinet Door Backs

Faint dark lines on the inside face of cabinet doors right at shelf locations are typically caused by deposits of dust. March 12, 2009

On our white painted jobs, the backside of our cabinet doors get a mysterious shadow line where they come in close proximity to the PVC edgebanding of the shelves. The shelf does not touch the door, but is about 1/8" away.

It's likely that the shadow line is also around the perimeter of the door where it would be in close proximity to the box PVC, but it's much less conspicuous. The line is grey in color and is not removable. The finish is a pigmented conversion varnish. Could it be some kind of chemical off-gassing of the PVC that is reacting to the fresh conversion varnish?

Forum Responses
(Cabinetmaking Forum)
From contributor W:
When you say a line do you mean like someone put down a 3/4" line of tape across the door or do you mean something that fades from white to gray back to white again? If it is a fading thing then I would think that it could be gasses from the PVC. If you have a solid line that has a clear start and finish point (like a tape line) then I would think that it has been set on something that caused the issue.

I was staining some doors and noticed a line across them. It was very faint but I saw it nonetheless. The door company was sending each door to me with a plastic band stretched around the top and bottom of each door - kind of like saran wrap. It keeps the doors from slipping around during transport I think. When I took the plastic off as soon as I got them, I didn't notice the line anymore.

From the original questioner:
This is not a crisp line, and I don't think it's telegraphing through four layers of conversion varnish from the raw door. Nor is it random, it is perfectly aligned to where the shelf rests behind the door.

From contributor G:

Seems you have a mystery. Are all the doors showing this line? Have you tried duplicating it by taping a strip of the PVC to a test panel? How long had the CV cured before the doors were hung? As an aside - four coats of CV on the backside of a door is overkill, in my opinion.

From the original questioner:
Regarding the four coats, we shoot a coat of primer/surfacer, then patch, then another coat of primer/surfacer, then two coats of conversion varnish. Perhaps we don't get the wet mill per coat that others do, but any less and it wouldn't look the way I want it to look. Specifically, it takes four coats to sufficiently hide the dark MDF corners on a raised panel.

From contributor B:
We get the same thing even on white melamine or laminate door backs after the cabinets have been installed for a while. It is dust! Try a little alcohol or other benign cleaner with a clean rag to confirm this. My guess is that the air circulating in the cabinet deposits the dirt where the space between adjacent surfaces is the smallest.

From contributor H:
I had the same problem in some cabinets we installed in a downtown location on a busy street and it is dirty air that is leaving a film as the previous post said.

From the original questioner:
Interesting, thanks guys. My installer confirmed that he was able to get rid of it with mineral spirits.

From contributor H:
It will come back until there is good air circulation in the home so make sure to advise the client.