Tech Talk #2 Adhesives, Glues, etc.

Let's talk a little about adhesives and "bonding" of two or more parts to make a structure. Bonding is simply the "gluing" of materials together to make a usable product. In "composites" that can be anything from using Portland cement to bond together sand and rock to make concrete or epoxy to bond together fiberglass and carbon, plus a bunch of other things to make a TT Hammer.

Concrete is a little boring so let's look at monoski applications. First of all, we have to be sure that everything is compatible. Simply stated the epoxy must bond well to all parts without causing any undesirable chemical reaction. Obviously wood glue would bond to the wood core but peal off of the plastic, composite, metals and fibers. Now, the only way to be absolutely certain is to test each and everything by itself and in conjunction with the other parts. We quite often find out that different preparation of the materials will give distinctly different results than we initially though.

As an example, I did extensive testing of adhesives for bonding composite panels and aluminum structures in commercial aircraft interiors. We got some very interesting results when comparing strength with surface preparation. One would think, the rougher the surface the better the bond? Don't believe for one minute that that is a universal truth. In fact it is far from it! With some metals, a rougher surface gave a significantly lower result in our testing.

So when we build skis, we test, test and test before we "set it in stone". In the very rare event that we have a failure of any kind in a ski, we can track it back and see if there is or was a variance from our specifications. If not, we are well assured that something outside of our control happened.

An example of this was two situations where the aluminum tail piece broke out of the ski. Remember in "Tech Talk #1" I mentioned how epoxy likes to bond to metals and my reference to "SPS" or Standard Process Specification? Well here's where it comes into play. We've used the same epoxy formulation for seven years, have the same fiber for three years, the same aluminum alloy for eight years and the same SPS for eight years in regard to preparation and bonding of that part into the ski and the same guy doing it since we started. Now, I ask the question. After several thousand successful process repetitions is there likely to be a failure at that point when everything has stayed the same? Obviously something happened to cause the failure and from there on it is very easy to track it down.

Let's go further into bonding and the different types of adhesives and some of the myths that are flying around out there. I look at adhesives (epoxies) as either "laminating" low viscosity and use to make a composite part and "structural" typically high viscosity and used to bond two structures together or also in repair.

Now, let's dispel a few myths:

#1- "Fast setting epoxies are weaker than slow setting epoxies". Not at all and define "slow" and "fast". It's all in the "chemistry". There are 90 second cure epoxies that have double the strength of 20 minute set or 8 hour set epoxies.

#2- "The higher priced ones are always better" Utter nonsense!! I know of 90 second cure epoxies that can be purchased off the shelf of you local hardware store for $1.99 that will blow away the "brand name" competition at $11.00 for the same amount.

#3- "Thicker is stronger than thinner" No, not at all true. In testing, we use several tests of which one is called an "overlap sheer" test. Simply put, two tabs of metal are overlapped and bonded together. When the adhesive is cured, we simply pull them apart and measure the results. I've got some excellent structurall adhesive that are very thick like Jello and have test results in the 3,000 pounds per square inch that drops as the part gets colder. On the other hand, I've got a water thin adhesive that gets stronger as it gets colder and at freezing temperatures has a test result of an amazing 12,000 pounds per square inch.

It all comes down to the right material for the right job and follow the manufacturers' instructions to the "T". I know, it's a "guy thing" but why not read the instructions first? You know, somebody got paid a whole lot of money to make all of the same mistake that you are about to make and he's just trying to save you a little aggravation.