LMI Yellow Glue - Luthier Tips du Jour Mailbag
In this episode, Robbie O’Brien answers a question about glue.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: There are so many glues available. Which glue do you use?
Robert O'Brien: Today's Tips du Jour Mailbag question comes to us from South Carolina. "Dear Robert, there are so many glues available that it can become confusing. Which glue do you use?" Mark in South Carolina.
Mark, I have used just about every glue out there, including hide glues, fish glue, LMI instrument makers glue, CA glue, epoxy, polyurethane glue. You name it; I've probably used it.
LMI Yellow Instrument Glue
For most of the applications in my shop, I use the LMI yellow instrument makers glue. It has excellent sanding properties, cleans up easily, dries harder than most other commercial glues, has excellent hold strength, and even has a discreet fluorescent dye additive that allows me to clearly see under a black light any invisible glue that can ruin my finish.
Surface preparation
No matter what glue you choose to use in your shop, one factor determines the durability of the glue joint, and that is surface preparation.
Adhesion and cohesion
The sticking and bonding mechanism is based on two key points: adhesion and cohesion. Adhesion is what holds together atoms and molecules of different bodies, in our case, wood and glue.
Cohesion is described as what holds together atoms and molecules of the same body, in our case, the glue. Cohesion we really can't do much about unless you're mixing your own glue. Of course, you want to pay attention to mixed ratios, and you also want to pay attention to expiration dates.
No adhesion
Now, adhesion, we can certainly do something about; we can directly influence that, make sure that the joint is clean and free of grease and oil. Now, this is very important when you're using oily, exotic woods like cocobolo. Most people like to wipe the joint down with acetone or alcohol before applying the adhesive. Also, when applying the glue, make sure that it is thinly and evenly applied.
If not, the bond strength can be affected, therefore compromising the strength of the entire joint.
Gluing guidelines
Mark, another common question that most people ask is, "How do I know if I'm using enough glue?" Well, I've got some guidelines here that may help you:
- If your glue works better as a lubricant than an adhesive, you're probably using too much glue.
- If you need to wear goggles when applying the glue, yeah, you're probably using too much glue.
- If you have more glue on you than on your guitar, then you could be using too much glue.
- If you have to use all 10 of your high-tech glue-spreading devices, then you're probably using too much glue.
- If you have glue stalactites and stalagmites on the inside of your guitar, then you're definitely using too much glue.
- If the set time of the glue exceeds the number of days in the week, then you're probably using too much glue.
- If you find yourself going through rolls of shop towels through the gluing process, then you're probably using too much glue.
- And finally, if you find yourself buying glue by the case and you're only on your second guitar, then you're probably using too much glue.
So thank you very much for your question, Mark. I hope this has been helpful.
[on-screen text reads: More Luthier Tips and online courses available at www.obrienguitars.com. Private and small group guitar building and finishing instruction available.]
