Glue - a simple term that describes a bonding agent
between two materials. The question is what two materials, are they
the same or are they different? If they are the same
substrates, contact the substrate manufacturer or representative for their
suggestions.
It's time to expand your vocabulary. Thermal
coefficient - the rate at which a material expands and contracts due to
temperature change. Unlike substrates will expand and contract at
different rates in heat, cold and humidity. About 4 years ago, I
created a 1 1/2" HDU carved sign for a friend. He told me that he
would install it above his doors at his barn in the country. I went
to town on this sign, after all he was my friend. I carved the HDU
with a CNC router and cut it to shape. As specified, I primed it
twice and painted it with a faux marble effect. It was beautiful, I
was really proud. My friend told me how happy he was with the sign
and that he wanted to install it from the inside of the barn to hide all
the fasteners. I said (being the sign guru that I am) let me mount
the sign to a piece of MDO, I knew that the screws would pull out of the
HDU over time. I cut to shape a piece of plywood, primed and painted
it. I took a tube of Construction Grade Cement that you would find
in a hardware store and using a caulking gun, spread it generously on the
backside of the sign. I then took the sign and plywood and clamped
them together. That weekend, I delivered the sign out to my friend's
farm and we installed it together. End of story, right? No,
five weeks later, my friend called me and told me the sign fell off the
barn. Impossible. I told him that I would take a ride out that
Saturday to see what happened. Sure enough, the plywood was still
mounted up on the barn and the sign lay below in three pieces.
Scientifically, this is what happened, the marine grade
plywood was wet (i.e. it was swollen). I applied the adhesive and
clamped the sign to the wood. The adhesive bonded to each substrate.
Over a five week dry and very hot period, the dampness in the wood
evaporated causing the wood to shrink (Thermal Coefficient). As the
wood shrunk, the adhesive cracked from the HDU until it's weight caused it
to fall to the ground.
Since this event, I began using 100% Silicone to bond HDU
to an MDO backer. The Silicone's properties allow for expansion and
contraction and hasn't let me or my signs down yet. Become familiar
with the adhesives in your shop, knowing their limitations will help you
avoid headaches down the road.
If you would like - e-mail me at info@signhunter.com and let me know if
this article was helpful.
Christopher Flejtuch
Signhunter.com
