Monday, November 8, 2010

Of glues and solvents

When it comes to models, a lot of people talk about the quality of sculpts and how far the injection molding process has come, but few people take the time to really consider one of the most important things in the hobby. How do you plan to actually assemble that $50 piece of styrene?

When the new (and rather stunning) Daemon Prince model came out, it was praised for its quality and the many customization options. I was at the Battle Bunker the weekend it came out and I saw a younger person assembling one of these fantastic models. I asked him to take a look at it, hoping to get a close look at the sculpt. Unfortunately, I was unable to really appreciate the model under the thick layer of glue coating it. Of course, one must wonder why he was even using glue in the first place.

To consider this question, we must first know about the different types of adhesives available. Here is a short breakdown and why you should use what when.

But he seemed so mild mannered!

The first and most common glue used in model assembly is cyanoacrylate glue, commonly called super glue or CA glue. This glue bonds best to smooth surfaces and fingers. The general tenacity of CA glue makes it perfect for attaching smaller pieces of metal models together but its low sheer strength makes it very easy to torque larger pieces apart. For this reason, many in the hobby drill holes and insert metal pins into larger metal models before using CA glue to seal the deal. It is available in many varieties, from the very thin to the gap-filling gels. With so many different options, fast drying times, and versatility in bonding dissimilar materials, every hobbiest should have some sort of CA glue on hand. Just remember to be careful with it, as it tends to be very exothermic (gets hot) if it is applied (or spilled) on cotton. Significant amounts can actually start fires!

not included - clamps, a free afternoon

Many people, frustrated with poor performance of CA glues on metals, decide to go the extra mile and use an epoxy. While found in many forms, epoxies always consist of two parts: a hardener and a resin. When these two parts are mixed, the resin begins to harden and bonds metal together with a rather amazing permanence. While very attractive for this reason, even the fastest epoxy adhesives take fifteen to twenty minutes to harden significantly and upwards of 24 hours to reach full strength. That is a long time to wait and a long time for something to go wrong. Many people opt to use epoxy putties, which operate under the same principal as the liquids but in a convenient play-dough format. These are very easy to under mix and generally don't adhere as well as the liquids. Best to avoid them unless you are using them to do some actual sculpting.

Also keep out of the reach of people who like to huff things in cans.

My favorite adhesive for the hobby is not actually an adhesive at all. It's what is called "plastic cement" or "plastic weld." There are many varieties for many types of plastics, but my favorites are ones featuring butanone (also called MEK), often diluted with acetone. MEK based welds work for most plastics and are generally rather high powered. What these solvents do is actually melt the plastic slightly. When applied sparingly to each side of a joint and pressed together, the plastic melts and fuses into a continuous piece. This results in a bond nearly as strong as the plastic itself. There are only a couple of concerns when working with plastic welds. First, you must understand that these solvents will not bond anything together that isn't plastic. It is literally impossible to glue metal together with plastic weld. Second, the fumes from plastic welds are very, very, VERY bad for you. It is recommended that you use these chemicals in a well ventilated area. Inhaling all of the fumes to store in your lungs and protect your friends and family is not recommended. Lastly, you must realize that plastic welds are very powerful and very thin. If you apply too much, some can soak into the space between your fingers and your model. The solvent will soften the plastic and leave a nice (and permanent) mold of your fingerprints on the piece.

Well, at least we know it's mine.

Once you have selected your glue, it is important to decide what type to get. I prefer thin glues because they have the ability to "soak in" and carry their way deeper into a joint, but I try to keep thicker CA on hand to fill any uneven gaps and provide a nice tight grab on metal models or metal to plastic. I use plastic weld for nearly anything else. Remember that less is more with glue and the smoother the surface the easier it is to grab.

To review, my work desk has three adhesives. A bottle of "control gel" CA glue for seam filling, some incredibly thin CA glue to do any bonding on non-plastics, and a bottle of MEK-based plastic weld with a brush to do most of the model work. What's on your bench?