Hi All, I've just finished conducting an experiment in an effort to
prove or disprove a suspicion concerning PVC-E glue and bellows cloth.
And while what I discovered might apply to other materials, I am not
making any claims in that regard.
My initial concern surfaced when I read an article about the basic
properties of PVC-E glue, and the one that caught my attention was
the one about how it creates the bond between the different materials.
Most basically put, the glue gets into the fibers of the materials
and as it dries, chains of molecules connect the two to each other.
Now, what caught my attention was the part about "when it dries"
because in other places I had read that the drying process involved
evaporation. In other words, the water in the glue has to evaporate
for the glue to dry (or polymerize).
That got me to thinking: If the glue is placed between two substances
that are air-tight, like -- for example -- glass, could the glue ever
dry? If air can't get to the glue, how can the water evaporate?
Ultimately, that led me to consider what happens when gluing bellows
cloth to bellows cloth -- like where the cloth overlaps at the hinged
end. So, I ran my first experiment.
Taking a small striker bellows, I recovered it in the normal fashion
using the PVC-E glue. After 24 hours I pulled the cloth apart at the
overlap; to my surprise, the glue was not 100% dry. So, I put on a
little more glue and waited two days. After the second day I pulled
the cloth apart again. And, while it had dried more than before, it
still wasn't 100% dry in the center-most area of the overlap. The
third time, I let it dry for a week, and this time it was finally
As a side note, that got me to thinking what must have happened over
the weeks' time that allowed the glue to finally dry. The only
conclusion I could come up with was that the air found its way to the
center area via microscopic 'channels' in the glue itself. So, that
led me to conclude that if air could get into the glue in the center of
the overlap, it must also be able to get out via the same 'channels'.
Next, I tried the experiment on motor cloth, and I wasn't too surprised
to find that the glue dried within 24 hours. I concluded that cloth
was thick enough and porous enough to allow the air to pass through the
cloth and get to the glue, allowing it to dry. Still, I came away with
the inescapable conclusion that if air can get in, air can get out.
Next, I ran the experiment using the heavy bellows cloth that I sell.
(By this time in the experiment, I was no longer covering bellows --
I was just gluing pieces of cloth together.) It is cotton on the inside
and acrylic on the outside. What I discovered was somewhat depressing,
and I'll try to explain this as best as I can.
First, the acrylic side if the cloth is 100% air tight because it's
synthetic, whereas the cotton side is neither air tight nor water
tight, because it's organic. However, because of the manufacturing
process, the natural rubber (between the two types of cloth) penetrates
into the cotton cloth, making it almost 100% air tight. So, after one
day, I pulled the cloth apart, and the glue was still wet. After two
days, it was still wet. After a week, it was still wet.
In frustration, I put pieces of wood on either side of the glued area
and secured them in place (like a clamp) with a large rubber band, and
put it in the microwave of 20 seconds on high. The wood got warm, so
I heated it for another 20 seconds. It got even warmer, so I put it
in for another 10 seconds. Then it got pretty hot (in fact, the cloth
curled at the edges that weren't covered by wood). Then I let
everything cool off for 30 minutes.
Well, I suppose I'm happy to say that the glue got 100% dry, and the
cloth was stuck together well enough that it was quite difficult to
pull apart. And, looking at the are where it was glued together, I'm
very confident that the seal was air tight. However, we don't have the
luxury of putting an exhauster or reservoir bellows in the microwave to
make sure the glue gets dry deep inside the overlap.
In closing, I'll let you draw your own conclusions about the use of
PVC-E glue (which, by the way, creates a mechanical bond) but it
brought to mind something I remembered reading some years back with
regards to one of the differences between PVC-E glue and hot animal
hide glue. So, I went back and found the article which was written
by (you guessed it!) Craig Brougher. In his article, "Gluing versus
Gooing", he wrote:
"The bond between hot hide glue and wood, leather, cork, rubber,
etc., is _not_ a mechanical bond! Yes, you read that correctly.
The bond which hot hide glue makes to all surfaces it attaches to
is a chemical bond. That also means that the material it attaches
to does not require roughness to make a good bond. It can be as
slick as glass. As a matter of fact, certain grades of hot hide
glue stick so tightly to glass that it spalls it when it dries and
shrinks, thus creating the art business known as 'glass chipping'.
You see, molecular bonding requires very specific kinds of molecules
to make connections with, and once they are made, that connection
becomes a stable chemical compound with the material it compounded
John A Tuttle
Brick, New Jersey, USA