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Installing Plastic Binding

General:

 I'm getting close to the end of these posts on building a guitar...  After this entry, my focus  will shift to finishing.  Last time I shaped the bodies of the other two guitars, and in this I will add binding to the corners of the third.

Binding is a strip of either wood or plastic added to the very corner of a guitar.  Often (usually on acoustic guitars, less so on electric) these strips also have "purfling" - which is a decorative strip or inlay on either side of the binding strip - I won't be adding any purfling here, just a simple binding strip to both front and back edges making this guitar what is known as "double-bound".

I've done some binding with wood on previous projects, but this was the first time I tried using a plastic binding.... To tell the truth, this is actually my second attempt at binding this particular guitar as I failed with the first attempt.  That was entirely my fault, mostly because of my frugality -  when ordering parts, I had included a couple strips of plastic cream-colored binding that measured 090" x .250" x 65" long (one for each side) and figured I would try make do with the rabbeting bits I already own to route the channels for them.  I knew I owned a set that had a bunch of bearings with it, so I figured there must be one in there I can use that's close.

The 1/4" depth obviously wasn't a problem, as that's just the setting for how deep to go.  The problem was with the .090" thickness of the binding.  The rabbeting set I have has bearings for 1/8" and for 1/16" deep (0.125" and 0.0625" respectively) - and the .090" binding falls right between those.   The 1/8" slot was far too deep, but I figured I would try the 1/16" bit and see how it worked out.

I know, I know.  I know better than that - but I did it anyway.  It was good practice...  but that's about all.  After I had the binding in place, it stuck out quite a ways/  I scraped it down (which went quite well, really) to where it was 1/16" thick, but it just didn't look quite right - and there were a couple spots where I scraped a little too much, and the binding subsequently became too thin - and at 1/16" it's far too easy to see a flaw like that.

So, I ordered a proper set of rabbeting bits (StewMac seems to be about the only place to get them) along with some new binding strips and re-routed the body with a correctly sized rabbet and went about reinstalling the new binding strips.

The plastic strips that came would never work as they came - they needed to be pre-bent to fit the guitar.  So I taped the center of the strip to the bottom of the guitar and worked my way around the body fitting the strip a few inches at a time, taping the binding strip as I went. 

To add a bend to the plastic is just a matter of heating the plastic until it deforms easily, then holding it in place while it cools.  It really doesn't take a lot of heat - I did this using a heat gun, but I think that was really too hot - a hair dryer would probably have worked better. I don't own one though - and didn't want to spend any more money for such a thing (but now that I think of it, I could probably have just checked out a couple local thrift stores and picked one up for a buck or two).

The tight curves at the end were the most challenging.  I just worked a few inches at a time, taping the binding as I went, making sure I could tape it with no gaps when it came time to do the same thing with glue. 

 The front will not require a splice, as the binding ends at the neck pocket.  The back does, however, and I figured about the best place for a splice would be behind the neck - the other choice being at the bottom of the guitar, though I thought with all the curves it might be easier to work with the binding at the end of it's run rather than in the middle.    I cut the binding strip to length where the two ends met, being extremely careful to make a perpendicular cut on each end.

 Then it was just a matter of gluing the binding into place - again, I started at the bottom of the guitar with the middle of the strip and worked my way up each side, taping it in place as I went, then let it sit for a full 24 hours to let the glue cure.  I used the Weld-On cement StewMac sells to glue the binding in place.

It went fairly well, at least for the most part. 

 When I was finished with the back, I repeated the process for the top of the guitar.  There were two significant problems I ran into.   The first was this: 

 Now how did I let that happen?  I thought I was so careful when cutting the thing to length.  Ugh...  To fix it, I cut a thin slice of binding strip and glued it into place - the glue literally melts the plastic, so it should be a sound repair. 

 When the glue was dry, I trimmed off the excess and scraped and sanded the joint so it was flush.  It does leave a little bit of a line, however.

I've read where you can take a small piece of binding strip and place it in a capful of acetone, which will melt the plastic giving you a little plastic paste you can fill small gaps with - this binding strip must be of a different type of plastic as I couldn't get it to do that...  It's not all that obvious on the guitar, so this will work.

The other significant issue I had with the binding was it didn't always adhere as well as I think it should have.  You can see it in the curve of the body in the photo where I cut the strip to fill above, and on the top I could pull the binding out here at the bottom of the guitar:

 That was disappointing, to say the least... I guess you can't expect what is essentially a PVC glue to hold all that well to wood.  To repair these gaps, I held the offending areas of binding out with my finger like in the shot above and wicked in some thin CA glue into the void, then held that all in place until it dried - problem solved for now, but next time I want a better solution.  I tested some glues, more on that in a bit...

To finish the binding was a simple matter of scraping it flush with the body, simply enough done with a hand-held scraper: 

 From here, it can be sanded and treated just as the rest of the body is.

I want to do this better next time - specifically, I want a better glue.  Now, some sort of plastic glue will be necessary to have on hand for purpose such as the repair above, where one is gluing plastic to itself, but for gluing the binding to the body, there has to be a better solution.  A little testing was needed...  First, a plastic glue or CA glue is commonly used for this purpose, so I decided to try a few different plastic glues against a gel form CA glue.

I had read somewhere that Testor's model glue was for all intents the same thing as Weld-On and could be used in it's stead - so I picked a bottle up at the local hobby store and by happenstance I was in the hardware store I noticed they had Duco plastic model cement, so I picked up a tube of that as well. I knew each would work well for gluing plastic to itself, but besides being a bit of a skeptic having not done much in the way of gluing plastic to wood in the past I didn't know how each would hold onto wood... So I set up a little test to see. I glued a short strip of binding to a piece of beech with each glue and let it set for 24 hours. The contenders were, in order:

#1: Weld-On
#2: Duco Plastic Model Cement
#3: Testor's Model Cement
#4: Loctite CA  (gel form)

First thing I noticed - the three plastic cements are NOT all equal. They each smell distinctly different, and carry different material warnings on their labels.

Now - this is wholly subjective, and I don't claim to be any kind of expert - my test was simply to pull the binding strip off of the wood to see how well each held on. For a rating system I'll use a 1 to 10 scale - let's say that this was a wood to wood joint done with wood glue as being the standard for a score of 10; a rating of 5 for the absolute minimum I would consider using;  and a rating of 1 would be a complete failure. My ratings for each glue would be:

#1: Weld-On
My rating: 5. It came off fairly easily, and while I wouldn't say it impressed me, I would think it to be sufficient enough of a hold to work (good because it's sold for that purpose!).

#2: Duco Plastic Model Cement
My rating: 3. It came off more easily than the Weld-On. I don't think I would use this stuff.

#3: Testor's Model Cement
My rating: 2. This stuff barely held. I definitely would not use it for binding.

#4: Loctite CA
My rating: 8. The CA held just about as well as I think you could expect any glue to hold plastic binding in place on a wood base. It wasn't as good as a wood to wood joint with wood glue - but the joint was very strong.

My take - The strongest was by far the CA glue - it's short working time would enable you to only glue a few inches at a time at best, but I think that's what I will use next time.

The Weld-On worked also - and while I wouldn't call it a "strong" joint, it does the job. I did end up using the Weld-On for this project, but was ultimately disappointed - I ended up fixing gaps where it just didn't hold well - using CA.

The other two - they just didn't hold nearly well enough for me to even consider using them.

Now, I had an idea of what held well and what didn't as far as those glues go, but I wanted to take it a little further - CA is a good glue, but it's working time is very short - so I decided to test a few more glues in the same manner to see what else might work.  Here, the contenders are:

#1: Titebond Wood Glue (original formula)
#2: Titebond Liquid Hide Glue
#3: Elmers White glue
#4: Loctite CA   (gel form)
#5:  Loctite CA (thin, regular style)

I didn't include hot hide glue - I didn't have any ready at the time I put the test together - but the liquid hide glue should suffice as a test for it as well, as once they are dry they behave very similarly.   Neither did I include polyurethane glue - I don't allow that stuff in my shop  - nor did I include any kind of epoxy, as you are just asking for trouble using that here, at least in my opinion. 

My ratings:

#1: Titebond Wood Glue (original formula): 
My rating:  1.  Total failure.
My rating:  ON HOLD:  Blast it.  It looks like my bottle of liquid hide glue has gone bad - it wouldn't fully harden.  It is nearing the bottom, and has made it through the hot part of the summer so I reckon it was time.  Liquid hide glue does have a shelf life... 
 
[UPDATE:  My rating:  1.  I finally got a new bottle of glue and tried it out on a piece of plastic binding. Once dry, it failed, utterly and completely.]
 
#3: Elmers White glue
My rating:  1.  Total failure.
 
#4: Loctite CA  (gel form)
My rating:  8.  It held as well as last time.
 
#5:  Loctite CA (thin, regular style)
My rating:  10.  It held as good as any glue is ever going to - the binding broke before it separated from the wood.
 
I was fully expecting the wood and white glue to fail, and it did, spectacularly.  However I was pleasantly surprised by the performance of the hide glue, even with it not curing fully...  While it didn't hold as well as the super glues, it looks to me that it might hold its own against the Weld-On.  Plus, it has an extended working time and is not as harmful to the finish as super glue.  I will have to re-test using liquid hide glue when I get a chance to pick up a new bottle, and I might include hot hide glue at the same time.  I will pick up a new bottle ASAP  and post the results here when I do.
 
[UPDATE:  As I mention above, once dry it failed, utterly and completely.  It must have been just holding because it was sticky gunk that just wouldn't dry, because once it was it let go as easily as the other wood glues .  I was hoping it was a sign it was going to hold, but alas it was not to be.]
 
I was also surprised at the difference between regular and gel CA glue - the thin stuff held - period.  It didn't let go at all.  The gel did, though took a little effort.  I expect the gel may still have an advantage because it is a gel, making it easier to apply...  but still...

Leif

Comments

Comment: 

Do you suppose the thin CA worked better because you were testing against long grain?  Or, more accurately, do you think that the gel CA would do better when you got around to the end grain parts?  I really don't know, that is why I'm asking.

Comment: 

The thin CA just held better - period, at least to my eyes.  I don't believe that grain direction mattered that much...  Either way, to get it off, you would either tear wood off the surface or leave scraps of binding on the wood.  It really held - whereas the gel did come apart at the seam between the two materials.  I suspect that converting the CA to a gel dilutes it somewhat...

For my part above, it might just have been that I didn't get enough glue on the joint or that I didn't get it taped securely.  That's another epiphany I had - next time I'll try reinforced packing tape - the kind you can see through (at least somewhat).

Comment: 

It is possible that the thin CA formed a better bond because it was thin. The gel type is used when some gap filling properties are required, and as such, there may be more glue in the joint than needed, weakening the bond. The gel should have the same holding power, but may require more clamping pressure to acheive that. Most of the average CA glues have a shear strength of around 1200 lbs/sq.in., if I remember correctly. Strong enough for most applications. The crux is the application. Were you using an accelerant?

Comment: 

No, there was no accelerant, and there is no reason in my opinion other than the glue itself as to why one held better than the other (and that it has some "filler" to act as a gel is my best guess, also).  It's not the first things I've glued together, trust me!  Though remember this was a very subjective test, and a real-world one (as compared to an un-real world?)  that I did it to satisfy my own curiosity...  Tape will have to suffice as the "clamp" for either/any glue...  I do think it would be far easier to use the gel, as I think the thin stuff would get all over on you when you are trying to put this long binding down.

It's really not that big of a deal to me - the gel held far better than the Weld On, just not quite as well as the thinner glue.  I would use it.  I just need to test the hide glue....

Leif

Comment: 

That Binding goop (as it's technically called) takes awhile to melt... like several hours if you are making enough to glue the entire length of binding to the guitar (prefered method of many a luthier). I think the key here is speed in set up... as too long a cure time leads to binding seperation.

 
Bruce

Comment: 

I've heard of that...

In this case, I was trying to make that "binding goop", but I only wanted enough goop to fill that little gap, not for gluing the entire thing...  I put a piece of binding in a capful of acetone, but it didn't dissolve.