glue

What you should know about High-Pressure Laminate (HPL) guitars

What you should know about High-Pressure Laminate (HPL) guitars

HPL, or High-Pressure Laminate materials are becoming more commonplace in guitar construction. Martin Guitars, in particular, have a line made partially, or almost completely, from HPLs. 

As a guitar construction material, there are a lot of advantages. But, in order to go into this with your eyes open, you should be aware of one disadvantage. 

Check it out…

Bridge Collapse

The saddle slot in some bridges is quite close to the front edge. In an ideal world, this might not be too much of a problem because, even though there’s a lot of tension from the strings, most of that is ‘downwards’ towards the bottom of the bridge.

Of course, it’s not an ideal world and, even though most of the pressure goes down, there’s always some that’s trying to tip that saddle forwards too. Things like the strings ‘biting’ into the saddle and actually pulling it forwards as you tune up can add to the problem.

And sometimes the bridge gives way. Like this.

The front edge of this bridge has sheared off

Now, I could just smooth off the fracture line and glue in a new piece but I don’t want to trust the glued joint to take that strain. It might be fine but I want to give this repair as much of a chance as possible.

So, I’m going farther back into the saddle.

My plan is to remove wood to the back of the saddle slot. I’ll glue in some new wood and then re-rout a new slot into that new wood. This way, the glue-line won’t be taking the strain.

You can see what I mean in the sketches below.

'Grafting' new wood to broken guitar bridge

New saddle slot will have new wood in front of and below

So, below is the bridge with the wood removed. I’ve sloped a section from the front of the bridge to the back, bottom corner of the saddle slot.

You can see the (slightly out of focus—sorry) shape of the piece I’ll be glueing in.

By the way, that’s just a thin piece of sheet brass that’s taped down to the guitar. It’s there to protect the top as I work on this.

The photo on the right below gives you a better idea.

New wood to be grafted on to bridge

New section will fit in like this

Clamping this one needed a little thought. As well as clamping downwards, I have to keep a pressure towards the rear of the guitar. That’s tricky though. I came up with this:

Inventive clamping to keep it in place

I clamped a block in place near the front of the bridge. The new bridge piece will bear off this and, as I clamp it down, this new piece will ‘wedge’ into place against the block. I can now get good clamping pressure in all the right places. Yay.

Once done, it’s just a matter of shaping the glued-in wood to the right profile and routing a new saddle slot.

I decided to make a new saddle too. The old one was actually an un-radiused classical saddle and it was made from a pretty soft plastic (the strings were digging in as mentioned above). A nice bone saddle will sound, play, and wear much better.

Hopefully, there's a long life ahead for this guitar. 

Reinforcing Floyd Rose Cavities

Removing a regular tremolo bridge and installing a Floyd Rose is something that most repairers will do from time to time. Going the other way isn't quite so common though. It's generally a bit more rare to uninstall a Floyd in favour of a non-locking trem. 

And, in this particular instance, it threw up an issue that had to be dealt with.

The Floyd was to be removed from this Strat and a new non-locking trem installed in its place. Firstly, this meant plugging the existing Floyd post holes and drilling for new holes a little farther back. 


Incidentally, here's something worth stating for the benefit of those researching this topic. You'll find information online that the Schaller 3801 bridge will retrofit a Floyd. This isn't the case exactly. While the 3801 shares the Floyd's unusual post spacing, its overall footprint is smaller and it will not intonate if you don't move the posts back as I've done here. You'll need to plug and re-drill 6mm farther back. Sorry—no drop-in retrofit for you.


This new post hole is dangerously close to the cavity.

When I drilled those new post holes (you can see the new hole overlaps the plugged one in front), the treble side hole was dangerously close to the cavity. I wasn't prepared to take the risk that this thin sliver of wood wouldn't crack or break in the future. 

Best to play it safe and add in a little reinforcement here. 

Because there's plenty of space between the new trem block and this front cavity edge, I shaped a piece of wood to run the full width of that edge—not just a chunk to glue into that recess behind the post. This should give things a bit more strength and further reduce the risk of catastrophes. 

Gluing reinforcement strip to trem cavity wall

Reinforcement strip in place

I'll sleep a bit easier knowing that this post is less likely to break through the cavity wall some night the owner gives his whammy a wiggle. ;-)

Repairing Loose Acoustic Guitar Braces

Visible gap on loose acoustic guitar brace

Glued inside the top and back of your acoustic guitar are braces. These are wooden support beams* that provide strength to what are, otherwise, relatively thin pieces of wood. 

Sometimes a brace can become loose. This could be because the guitar gets a knock but, often, some or all of the glue can just fail for a variety of reasons. 

A loose brace can be a pain. If part of the guitar isn't properly supported, it can pull and warp in unpleasant ways. That's generally not good. In addition, one symptom of a loose brace (and frequently the one that leads to its being discovered) is a nasty buzz or even a rattle when some or all notes are played. Often this buzz is located around a certain note (a tone or so either side) as the loose brace vibrates in sympathy. 

These can be an incredibly frustrating thing to track down. Sometimes you'll get lucky and be able to see the gap between brace and top/back (like in the photo at the top—the shadow beneath is clear) but, more often, you'll end up, up to your elbow in the sound-hole, poking at joints with a feeler gauge, trying to find a tiny gap. It's a real pain. 

When it's found, the gap should be cleaned and the old (failed) glue removed. Then, fresh glue is worked underneath the brace and the repair is clamped up to cure. This sounds straightforward until you try doing it, at the limit of your reach, blind (or, with an obscured reflected image in an inspection mirror).

Loose acoustic guitar brace

Find loose guitar brace

Not so with this one, though. These are back braces and they're relatively easy to get at. This particular guitar did actually get a knock and has had a previous repair for a back/side separation. I can't be certain that these braces were knocked loose at that time but it seems likely. Maybe not, though—benefit of the doubt for the previous repairer.

You can clearly see the feeler gauge poking under the braces in the photos. The blue tape is something I've put in, by the way. It keeps the mess down when working glue under the brace. 

Once there's a good smearing of glue in there (and it needs to be worked well under to get a good joint), a bit of a wipe up, and then it's clamped (see below). The little scissor-jack thing is a god-send for these jobs—it gives decent clamping pressure and I can wind it up from outside the sound-hole. 

On this particular instrument, this has to be repeated a few times as I found four loose ends. But not any more more. All re-glued and sorted. 

Glueing and clamping loose back brace on acoustic guitar

*I think 'beam' is the correct structural term for guitar braces but any engineers can feel free to correct me. Beam tends to make most people think of massive steel joists, however, while guitar bracing tends to be a little smaller. And wooden. 

Headstock Repairs - More on Reinforcement

So we've looked at a neck repair with an overlay for reinforcement. Let's have a look at the other main method of reinforcing a broken headstock: Splines. In guitar repair circles, splines are long (relatively speaking) narrow pieces of wood that are glued into corresponding channels to provide additional strength.

Failed, previous repair

Nasty glue residue on failed repair

The first repair is the important one.  

Remember these wise words. If the first one fails, it usually complicates any subsequent repair. This guitar arrived in the workshop with its headstock flapping about, held on by only some gummy bits of glue. There was a LOT of residue to clean up. Too much, really. Any glue I apply to repair this break needs to make a good contact with the wood. New glue, trying to grip a film of old glue is a recipe for a poor repair.

Even after cleaning up much of the earlier stuff, I felt some reinforcement was necessary to ensure a sound and lasting repair.  

Determining the truss-rod location with a magnet

Glueing up the peghead before splines

As it happens, the diamond-style volute on this instrument provided me with the perfect idea for reinforcing things. I can rout a channel through that and carve the spline to the same diamond shape. Nice and discreet. Splendid.

First up, I have to keep the truss-rod in mind. I don't want to accidentally rout into a hunk of metal. The magnet on the back of the neck tells me where the rod ends. I note that and get on with getting things back in one piece.  

Diamond volute to be 'splined'

Inset, rough-cut spline

You can see the diamond volute pretty clearly above. I'm not going to take the whole diamond—I'll effectively rout a channel through it and farther along the neck (past the break). 

It's an easy job to shape a piece of mahogany (the spline) to fit this channel. Then a little carving will replicate the original shape. Clean up, slap on a bit of lacquer and we should be able to avoid any more strings of gummy glue.

Spline reinforcement on guitar neck break

Headstock Repairs - Reinforcement

Broken Gibson headstock repair

We've talked a lot about neck resets over the last few weeks so let's move down the other end of the neck. Headstock breaks.  

Nobody likes to see it happen but sometimes your guitar takes a tumble and the impact can—all too easily—snap the headstock. In most cases, this is a (reasonably) straightforward repair and can be re-glued soundly.  

Sometimes, though, the nature of the damage can force us down a more 'involved' path. If the break is 'short' (i.e. it doesn't provide a lot of glueing area to ensure a sound repair) it may be necessary to consider some reinforcement to ensure the repair holds.  

One solution is what's called a 'backstrap overlay'.  

This involves overlaying some fresh wood over the repaired break. The new wood glues onto the unbroken wood either side of the crack to add strength.  

Let's take a look at one. 

Reglue headstock before applying backstrap

Remove wood to accept overlay

In the first photo directly above, I'm repairing the break. This might seem odd but I need to get everything back together properly before I apply any reinforcement. The repair is carried out as it would normally be since the actual re-gluing isn't the real problem—the problem is keeping it in one piece after string-tension is applied. I need to glue-up everything as normal and then reinforce things to ensure the repair is strong.

When the initial repair is done and the glue has dried, I can begin the real work on this one. I remove a few millimetres of wood from the rear of the headstock and, past the break, along the neck. It would make for a more discreet repair if I brought this all the way to the end of the headstock but, on a Gibson, I like to stop short of the serial number. If the guitar is ever sold on, a perspective buyer may be put off more by the lack of a serial number than a well-executed repair. 

The photo above on the right shows the removed section. I'll inlay the new wood here so let's get on with that.

Clamping for backstrap overlay on Gibson neck break

New wood overlaid over broken neck

The wood to be overlaid on the headstock is thicknessed and cut to the rough dimensions. To accommodate the angle between headstock and neck, I bend the new wood. It's this bending that adds extra strength to this repair as the wood grain curves to the correct angle.  

Repairing guitars often makes for some intricate clamping setups and overlays are prime culprits. A shaped caul is useful to get the wood in that curved bit glued in properly. The roughly shaped wood overlay is pretty obvious (and pretty ugly at this stage) in the photo on the right. 

Newly inlaid wood cut to shape on headstock

Tuner mounting holes drilled in overlay

This is where things take shape (pun intended). The overlay is cut to shape and the tuner holes drilled.  

At this point I can go through the usual finish prep. Grain-filling, sanding, etc. In cases like this I need to match the colour of the original finish on the newly overlaid wood. I also have to manage the transitions between new and old finish carefully to keep things looking as inconspicuous as possible. Sealer, colour, and a number of clear-coats later and I'm ready for the next step. 

Waiting.  

Have to wait for the finish to cure properly. Then sanding and buffing and polishing and reassembling and stringing-up and… 

Playing. 

All is well with the world.  

Gibson headstock break repaired with backstrap overlay

Les Paul neck repair with reinforcement

Gibson Neck Reset - Curveballs

The last word on neck resets for a little while. We've had the theory. We've had the straightforward neck set on a Martin and we've had the Martin neck reset that fought back a little. 

Let's take a look at a neck reset that threw up some curveballs along the way. 

On a Gibson acoustic guitar, the job of getting the neck off is generally a little more work. As well as glueing the actual dovetail joint, the folks at Gibson also apply glue to the surfaces between the neck-heel and body-sides. Also, they glue the neck in and then  lacquer neck and body together. This means getting through the lacquer safely when removing the neck, and—more often than not—means some light finish repair work after it's all reassembled. A Gibson is more work to reset but is still generally straightforward. 

Generally… 

First up, this guitar has a couple of longitudinal cracks in the top. These have been there a while and have had a previous repair before I got the guitar. I check the repair and it seems sound so I move on. I also note that there is a small gap between the bottom of the heel and the body-binding. I can't tell too much about this now and it's clearly been there for some time so I pop it in the mental notebook.

I won't go into detail as I've covered much of this before. I free up the fingerboard extension, drill my steam access hole and get to work. 

Something's not right.  

As soon as I give the instrument its first 'encouragement wiggle', I can tell that something is wrong. 

Applying steam to loosen glue on neck dovetail

Applying steam to loosen glue on neck dovetail

Neck block has come loose internally

After some investigation, the issue becomes clear. The neck block (the solid hunk of wood that supports the neck inside the guitar) has become loose. The guitar's top and back are no longer glued to the block and any pressure I might apply to remove the neck is also going to push the block up against the top until it breaks.

It seems likely that the existing top cracks happened either because the block was loose and not properly supporting the top or (more likely) occurred at the same time as the block became loose—probably in a fall. Either way, I don't want to make things worse. 

You'll notice in the photo above right that I've removed the fingerboard extension (and that palate knife shouldn't be able to slide in like that). However I proceed on this job, I need to re-glue the neck block but I'm now concerned about unduly stressing this guitar top any more than is completely necessary. Removing the fingerboard extension will allow me to support the top as I remove the neck. 

Re-glue acoustic guitar neck block

Supporting guitar top while removing neck

You can see that support in the photo on the right. The dovetail-shaped slot cut in some plywood lets me ensure that the top doesn't move as the neck joint is separated. That separation is a slightly slower job now, and a more careful one.  

Once the neck is out and I've cleaned up the joint, I can glue the fingerboard extension back on to the neck (using a sliver of rosewood to take up the space of the fret-slot I used to cut through. This slot will be re-cut after things are back together. I go though the normal neck reset process from here.  

Dovetail and socket 'mismatch'

This Gibson has one more curveball to throw at me though. As I alter the neck angle, the bottom of the joint becomes looser in its socket than I'd generally have expected (a little is quite normal). Turns out, this dovetail's not the best fitted joint I've ever seen. The dovetail (the male part of the joint) is quite a bit shorter than the socket it mates to. I'm going to hazard a guess that this may have contributed to that little gap between heel and body-sides I mentioned earlier. 

Not a major problem. Some shimming is pretty much always necessary during a dovetail reset. Done properly and I've got a heel that contacts perfectly all around.

Better than original. Nice. 


Weak Neck Fail

repair guitar neck

This is a particularly handsome Heritage 535. It would be even more handsome if it were in one piece instead of two, though. The neck's come off and a little bit of investigation shows that it never stood a chance. This neck joint was weak from the start.

These joints are referred to as 'mortice and tenon' joints. In this case, the tenon (the bit at the end of the neck) was too small for the mortice (the 'pocket' in the body). As well as having a relatively large shim on one side, the tenon didn't make contact with the bottom of the pocket. There's an gap of a couple of millimetres between the two.

You can see the circled bits in the image. On the left is a chunk of mahogany from the tenon that's split off and the glue line is visible on the right. You can see the gap.

That gap means no glue joint there. Only the sides are glued (well, those and the 'face' of the joint but that's not providing a lot of strength).

This is a weak neck joint that was much more prone to fail that it ought to have been.

Rather than just gluing it back together, I'm going to build up the tenon to get this joint to where it should have been from the factory.

guitar neck tenon break
neck joint failure repair

First off, that little chunk of mahogany that's still glued to the side of the neck pocket has to be removed and glued back to the neck tenon. Once that's done, I nab a new bit of mahogany and thickness it so that it will fill the gap.

In the right photo, you can see I've glued this on and cut it to match the shape of the existing tenon. The thickness of the added wood gives you an indication of how much of a gap there was.

fix guitar neck joint
repair guitar tenon joint

I removed the old glue from both parts and re-glued the neck to the body. Because the break was quite clean, only a little touch-up work was required to get the guitar looking its best.

This repair looks good and, importantly, has actually resulted in a better, more sound, neck joint than when it left the factory.

Les Paul Neck Removal and Repair

les paul broken neck heel

Yikes. If you've been reading my stuff for a while, you've probably spotted a few different examples of neck breaks. Most of these have been up at the headstock end as that's the more likely place for a break.

It can happen down the other end too, though. This Les Paul took a tumble and broke in a nasty way. The exterior damage is obvious but it's pretty certain that crack extends into the neck tenon too (the tenon's the bit that gets glued into the neck pocket in the body).

This neck needs to come out to be properly repaired.

It's not too often that I need to remove a Les Paul neck, which is lucky as it's a relatively involved job. With a strong cup of tea to steel myself, I set to work.

les paul heel repair frets
les paul neck removal

First up, a few frets need to come out. To remove this neck, I need to soak and steam the glue out and that means getting access to the internals of the neck joint. I do this by drilling small 'access' holes. These are drilled in the fret slots. When it's all done, I'll fill the holes with rosewood plugs and re-cut the slots. All of this is hidden by the refitted frets.

Your eagle-eyes will have noticed a little dot on each (numbered) fret. These frets will be refitted and the dot tells me which is the bass end.

Keeping fingers crossed, I take a look under the neck pickup, hoping for a long tenon. No luck. If I could have seen the end of the tenon, I'd know exactly what size it was so I could position my holes to accurately access the sides of the neck joint  (if it's not clear what I mean here, a photo later on might clarify things).

Since all of this tenon is hidden, I have to measure out the usual Gibson size and position for this guitar and hope that it's built properly to spec.

In the photo, above on the right, you can see the pencil marks I've used to plot out the tenon and the holes I've drilled to get access to the joint.

gibson neck removal
steaming off gibson neck

This one's a bit weird-looking, I'll admit.

In the left image, I'm using a syringe to insert boiling water into the holes I've drilled. I give it a few seconds and then suck it back up again. What comes out is cooler water with some manky-looking dissolved glue. I repeat this process a lot over the course of a couple of days. A Les Paul neck joint is a hell of a strong joint and doing this gives me a little bit of a head start before I hit it with the steam.

Which is what's happening on the right. That nozzle lets me get piping hot steam deep into the joint. The heat and moisture helps to dissolve more glue and, after some time and work, the glue eventually lets go…

les paul neck tenon
les paul neck joint repair

…Leaving most of the bloody tenon still in the pocket. D'oh!

The heel crack extended into the tenon as we thought. Now I have to keep working to get this piece out with pretty much no leverage.

More tea required, I think.

Some steamy swearing later and it's out. Now, in the side of that neck tenon, you can see the tracks of those holes I drilled earlier. We were right on the money with the positions too—nice.

gibson guitar neck tenon repair
les paul neck joint fix

And here's the jigsaw we need to get back together. You'll notice a small shim in the neck pocket. This was installed at the factory (it's not uncommon) and I'll reuse it for this repair.

All of the old glue is cleaned from the mortice and the tenon and then, the two bits of neck are glued back together. Again, the tracks of those access holes are clear in the photo on the right.

gibson neck tenon repair
les paul repair touch-up

Once it's sound again, the neck is reattached to the body. Those frets are reinstalled and all the frets are levelled to ensure clean playability.

Then, it's just some touch-up to hide the evidence. As the rear and neck of this Les Paul are black, the opaque colour easily disguises the repair.

It took a bit of thought, a lot of work and twelve buckets of tea but this job's a good 'un.