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
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?
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
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.
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!
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:
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
Always glad to help.
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. <G>
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.
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