Door panels CUPPING during DRY season??????

[blueman]

We have 2-over-2 paneled interior doors in our 125 year old Italianate house. We have only lived in the house for 2 years, but now for the first time I am noticing that many of the panels are getting severely cupped.

I am surprised because now the house is at its maximum dryness and I would have expected more cupping during the summer as the panels expand against the door frame.

Is it natural to have such cupping and if so what would be causing it?

I assume that since the house is so old and since I didn't notice the cupping in the summer months that this is just cyclical and will resolve when the humidity returns, right?

Thanks

[mm]

If the door is properly built -- I'm sure it was -- there is adequate space for the panels to expand. Sometimes people naively glue panels into place, and this can cause big problems.

IIUC painting and varnishing of panel door should be done lightly at the places where the panels meet the doors. So one won't see a ridge when the panel shrinks.

As to sealing the door, shouldn't that be done when the humidity is intermediate for the location of the door? Does that make a difference?

[blueman]

I'm sure it is. The panels are floating.

Cupping in the sense of grain on panels is vertical and the panel is (cupped or bowed) similar to the way a 1x10 piece of pine would be said to be cupped.

I'm sure it's nothing since the house is so old, the doors are varnished (not painted) and the last coat of varnish was at least

10-20 years ago.

The house was of course built before electricy and central heat but again nothing has changed in the interior environment (as far as the doors are concerned) in a long time so I am assuming this is just part of the natural cycle.

My only question remains is what would cause cupping during the "dry" months (here in New England it is still winter and with forced hot air, the humidity is very low in the house maybe 20-30%) vs. the summer when it gets quite humid since we don't (yet) have central air.

[blueman]

Nope -- plus this is the first floor of a 3 story home with basement. Basement is dry and no signs of leaks on any of the floors...

[blueman]

I agree. But again I would have thought such "cupping" would occur more during the wet months when the panel would be expanding against a rigid frame.

But perhaps what is really happening is that the panels are quite thin (I would say 1/4" or less) with dimensions of maybe 36" x 12" from a single piece of wood (no laminations or joints) so that perhaps the natural stresses in the thin wood panels lead to such cupping during the dry months. In fact, several of the panels have cracks in them which presumably have occured over the past 125 years or so do to stresses, seasonal changes, abuse???? -- I guess this is understandable in large thin panels like our doors.

[George]

Not unless you're air conditioned to dead dry and the outside's in the rain. Right now my relative humidity is 84% outside (snow, too), and 28% inside. Don't think it'll ever get that bad with the opposite sides of the panel in the summer.

Got too dry on one side. Weathering? Lots of humidity cycles shouldn't make cracks, only extremes.

[Jim Weisgram]

[...snip...]

[...snip...]

Hmm, if it was just a change in humidity, the panel would expand equally on both sides, no cupping.

Perhaps you have a difference in the finish on the back side vs. the front, so the panel moves more on one side than the other. How are they finished, front and back?

[George]

There are, after all, _two_ sides to the panel.

[Jim Yanik]

Jim Weisgram wrote in news: [e-mail]:

not considering the GRAIN direction of the wood. Now if the panel was quartersawn,then you would get little or no cupping.Flatsawn wood will cup because of the curvature of the wood grain.

[blueman]

Both sides are varnished and I have notices this now on most but not all of my doors (and again these are all interior doors with not appreciable difference in atmospher on the two sides). The degree of cupping varies by panel -- some are quite severe, others are less so.

Again the only thing I keep coming back to is that the panel is a single large but thin sheet of wood so that it may not take much "differential" stress to lead to such cupping.

[Jim Weisgram]

[...snip...]

You know, your first statement about these panels implied the cupping was recent; but if it is just that you are now noticing the cupping, and it was there all along, then perhaps what you have are panels that were formed long ago from wood that was not dry enough, or wood that was reactive enough, to warp after the panels were formed.

Otherwise, it seems odd to have panels decades old all start warping at the same time.

Regarding your other comment, that these are interior doors and the panels are all indoors, so why is one side different than the other ... I may be belaboring the point, but ... say you removed all the finish from one side, and left all the finish on the other, then you have a panel that will change humidity quickly on one side, and slowly on the other, and the shrinkage/expansion on one side could be fast with little change on the other, and you get a warp when the humidity changes, and then the warp flattens out as both sides equalize humidity.