Effect of high humidity on wood?

[Jeff Wisnia]

It's been hotter than Hades here in the Boston area for the past week, we broke the all time high temperature record on July 19th. And, the humidity has been so high that if we take something out of the fridge it immediately is covered with lots of water condensed on it.

Even with our two heat pumps running full bore, it's still noticeably warm and humid inside our home.

Anyway, last nite SWMBO and I were watching the eleven o'clock news when we heard a fairly loud "thud" from somewhere in the house. I had no idea what it was, nor did she, so we just gave each other a WTF look and shrugged it off.

When we went upstairs for sleep I glanced through the open doorway of a spare bedroom and saw that one of my mom's original oil paintings had fallen from its location on the wall where it had hung for probably 25 years or more. It was a rather large painting, about 5 feet wide and 3 feet high, in a traditional wooden frame, it feels like it weights about ten pounds.

What happened is that the eye screw securing one end of the picture wire had pulled right out of the frame wood. No one was there fiddling around with that painting when it fell.

Granted, whoever selected those eye screws to use on that picture 35 or more years ago picked ones that were about the smallest size available, the threaded section is only about 5/16" long. But, I can't think of any reason other than the extensive period of high humidity "softening" the frame wood enough to cause the the weight of that picture to make the eye screw pull out.

I've already shuffled a pair of heftier eye screws out of my "hell box" and will fix things by tonight.

Do you agree with my thoughts about high humidity being the straw that broke that camel's back?

Jeff

[DerbyDad03]

Or its time for a seance.

[Home Guy]

Heat pump.

ha ha.

It's time for a real A/C that can bring down the humidity in the house.

alt.fan.cecil-adams ?

Who the hell is cecil adams, and why does he deserve to have fans?

[passerby]

You, sir, and your lady have nerves of steel or that must've been some riveting

11 o'clock news coverage. I would not be able to continue watching anything, let alone the normally depressing 11 o'clock news, until I found the source of any unusual noise in the house, it would just drive me nuts!

[nestork]

Moisture DOES cause wood to soften, but I'd be more inclined to think that the picture fell because the wooden frame got heavier rather than because the wood got so soft that the screw threads pulled out of the wood.

PS: You don't need to know the rest.

Wood is a natural material that swells and shrinks with changes in it's moisture content. When a tree is alive, the hollow wood cells are mostly to totally full of a liquid which is mostly water. There are also H2O molecules inside the wood cell walls that are bound to the cellulose layers (called "lamalae") by hydrogen bonding.

When you cut the tree down, initially the water evaporates from the hollow wood cells. During this period, the wood becomes significantly lighter in weight, but it doesn't change it's dimensions. It is only after this free water inside the wood cells evaporates that the H2O molecules hydrogen bonded to the cellulose layers of the wood cell walls start to "evaporate" (for lack of a better word) into the surrounding air. As those H2O molecules evaporate, the lamalae get closer together, and the result is that the wood cell walls shrink in thickness. The hollow inside diameter of the wood cells doesn't change; it's only the cell walls that become thinner. And, just like a cellullose sponge becomes stiffer as it dries out, the wood cell walls become stiffer as they dry out too, making the wood stronger.

Since wood cells are shaped like long narroe drinking straws that are pinched off at their ends, you encounter far more wood cell walls as you go across the grain of wood than you do as you go along the grain of wood. Consequently, wood shinkage along the grain of wood is very small compared to shrinkage across it's grain, and in most engineering designs involving wood, longitudinal shrinkage is ignored. One place where longitudinal shrinkage of wood does cause problems is in truss uplift, where the long chords that run under the roof sheathing get slightly longer, causing the middle of the truss to be pulled upward.

Anyhow, you're correct in saying that wood does get softer as it's moisture content increases, but I'd suggest that the greater factor in this case would have been the frame getting considerably heavier as the wood absorbed moisture from the air. Perhaps it was a combination of the frame getting heavier and the wood getting softer, but in my view, the dominant factor would have been the frame getting heavier.

[dpb]

...

...

No. RH had/has nothing to do with it...it simply finally pulled out owing to more weight than screw thread over time.

[David L. Martel]

Jeff,

Wood swells with high humidity. This would make the wood grip the screw tighter. The low humidity that you may experience during the savage winters of you're frozen clime will cause wood to shrink, which may loosen the screw. Cycles of shrinking and swelling over the years may cause fasteners (both nails and screws) to fail. At any moment your home may collapse. Run. Of course the high humidity and the picture event could be unrelated coincidence. Always glad to help.

Dave M.

.

[dadiOH]

"Jeff Wisnia" wrote in message news:A6mdnYhvbsGq23HMnZ2dnUVZ [e-mail]

No. I would agree with 35 years of stress and aging on an indequate fastening and wood.

[Dan Espen]

I'm with this poster and at least one other. It was just time for the painting to fall.

[Jeff Wisnia]

I guess I'll go with the "its time had come" answers.

But it is the only time I can remember anything other than maybe a light bulb failing without some noticable activity taking place to prompt the failure at just that moment.

Well, maybe an overweight moth had landed on that picture frame....

I've replaced the eye screws with larger and longer ones and the picture is back up on the wall for the rest of the time we're in this home.

By the way, I discovered another tomato-tomahto thing today. Googling either "screw eye" or "eye screw" brings up those fasteners, different sellers call them one or the other.

Jeff

[Vic Smith]

I'll make it +2.

[Stormin Mormon]

Or its time for a seance.

[jeff_wisnia]

No, not getting interested enough to immediately go running around looking for what made that noise is just a normal effect of aging.

See my explanation here:

Jeff

[jeff_wisnia]

I think we've all "saucered and blown" this subject to death. So for now I'll just say:

THE END

Jeff

[Robert Green]

I would say it was a combination of the wood aging and the screw-eye responding to years of vibration. Screws depend on friction to hold, and each passerby vibrates the screw and can eventually cause it to loosen because the weight of the picture is constantly trying to "unscrew" the screw. That's why Locktite exists. (-: Screws have been loosening themselves forever, from both wood and metal and metal's not likely to respond to high humidity. It also sounds like the original choice of materials was not suited for the job at hand.

If you ever had street paving done, you know how much pictures rattle around on the wall when the use a compactor. The weight of the frame plus 25 years of vibration could have easily loosened the screw-eye enough to have pulled out, especially if it was undersized to begin with. Would heat or humidity effect it? Sure, different materials expand at different rates from the heat. In this case, though, I think it was just time and the natural tendency of a screw under load to unscrew itself.

[The Daring Dufas]

God is angry with you Yankees, He/She moved Boston to Alabama. Welcome to The South y'all! ^_^

TDD

[The Daring Dufas]

As I've gotten older, I've found that there are fewer people I wish to kill. All those assholes are dying off all on their own. ^_^

TDD