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. 

Plugging Holes for Fun and Profit

Mounting holes misaligned. These need to be plugged and re-drilled in the correct place. 

Mounting holes misaligned. These need to be plugged and re-drilled in the correct place. 

Despite the wonders of jigs and templates and CNC machines and whatever automation magic you can dream up, somewhere in the chain is a human with a brain of squishy meat and the potential to drop a spanner. 

Sometimes things are misaligned in the world of guitars. It's rare to fit an after-market pickguard without having to plug and re-drill at least one screw hole. New tuners? Get the drill. Fit a Floyd? Ah, crap. 

The tun-o-matic bridge mounts need to be properly placed so the original holes must be plugged.

The tun-o-matic bridge mounts need to be properly placed so the original holes must be plugged.

Misplaced and misaligned bridges happen too. They can cause some serious hassle for the player. That trem in the image above is not going to be the most reliable for returning to tune for instance. 

Tun-o-matic bridges can sometimes be found loitering in completely the wrong position too. And not just on Gibsons. This mahogany-body Tele on the right is a cool little Gibson-like Squier. It'd be cooler if the bridge was in the right place, though. Cue the cutting of wooden plugs, the plugging of holes and the re-drilling of correctly-placed mountings. 

Wherever possible, it's best to plug holes with the same wood as the material you're plugging. If the plugged repair will be visible, it's nice to match the grain of the surrounding wood as much as possible to minimise signs of repair. 

Plugging with hardware-store dowels isn't generally the best route. These are typically made of soft wood and you'll usually end up with end-grain showing in the plug. This tends to stick out like a sore thumb in a repaired surface and is best avoided, if possible. 

Cut your plugs from matching wood wherever you can. Always use hardwood plugs.

Cut your plugs from matching wood wherever you can. Always use hardwood plugs.

If you're doing your own plugging, cut your plugs from matching wood when you can. It's possible to increase the size of the hole to be plugged to match the size of your plug. If you go this route, be very careful—drill bits can wander and guitar finish can chip. 

Take it slow and easy. Good advice in guitar repair and in life.  ;-)

A better plan—if you've got a hole that's a different size to your plug-cutter tools—is to do things the old-fashioned way. Good, honest, whittling. 

Cut a long, square-section of hardwood, just bigger than the hole to be plugged and get carving. Knock off the corners over and over until your four-sided section becomes eight, becomes sixteen, etc. A good, sharp chisel will give you better control than a knife. When you're almost round, switch to sandpaper. A good fit is important, so don't be tempted to go with something too small. 

Go, my friends. Go and plug with confidence. 

You can carve a square-section piece to a round.

Repair To Damaged Fingerboard

Rather invasive repair for cracked heel

This venerable old girl suffered a cracked heel at some stage in the distant past. As you can see, the repair wasn't the least invasive solution that could have been imagined at the time. 

These big-ass screws have kept it (sort of) together but the instrument deserves better. I'm not going into detail on the heel repair here—take my word that it's all glued up and sound. Instead I want to look at how we can minimise the damage those screws have caused.

Damaged guitar fingerboard repair

Damaged guitar fingerboard repair

With the screws removed, things don't look too pretty, do they? Incidentally, the two small holes in the fret slot are mine—I drilled them when trying to steam out the neck to repair the heel and they'll be plugged and covered by a fret. The medium hole is a loose pearl inlay dot that'll be replaced later. 

The holes we're worried about are those big, jagged ones.

Of course, we could squidge a pile of coloured filler into them and smooth off the top but that's not going to be the nicest looking repair. We could cut some plugs and glue them into the hole. If we get a reasonable grain match, that'd be a better option but still not the neatest. 

What we're going to do is to replace the entire section of fingerboard between these two fret slots. Effectively, we're going to remove the rectangular section with the damage and *inlay* new wood. 

A bit of digging around my rosewood stock (and scrap pile) turns up a piece with a similar colour and a pretty close grain match.

Inlay good wood to repair damage to guitar fingerboard


If you look closely in the photo, you can see that I've actually routed out the damaged part but left a tiny sliver along the sides of each side. That sliver will keep a nice contiguous look along the edge of the fingerboard and save messing about trying to match the aged lacquer.

As luck would have it, this instrument needed a refret too. It'd be much more difficult to accomplish this well without refretting.

You can see the new fingerboard wood in the photo below. It's a good match for colour and grain and, once it's all clean and oiled, it looks pretty damn good. Stung up, you'd be pretty hard-pressed to notice anything. 

Much better than filler.

Guitar fingerboard repair

Bespoke Bridge

IMG 2959

Let's be honest, that's not an attractive bridge. It's seen a lot of action over the years and it's cracked and, somewhere in the distant past, it's had some gunky filler splodged in to try extend its life. And it's actually a slightly odd bridge. Although it has six holes for bridge pins, you can see along the back there are some filled holes as if this bridge were once strung from the top. There are also two little pearl dots which are usually present to hide small bolts (as they do in this case). These bolts are generally used on bridges that string from the top. But, then, why the bridge-pin holes?

It seems likely that the manufacturer repurposed this bridge from another model, filled the string holes and installed with bolts as normal. Fair enough.

This is all an aside anyway. On to the real work.

The owner wants this sorted but I wasn't able to source an off-the-shelf replacement. This means custom-malking a replacement.

custom acoustic guitar bridge
acoustic guitar bridge fix

Getting these things off is a pain—as well as the two little bolts under the pearl, this manufacturer epoxies the bridge in position. I may have used swear words.

Once off, though, I grab a nice piece of rosewood and thickness it to about the right height. I carefully measure and mark off the important dimensions, particularly the pin holes and the bolt holes—if these are misaligned or misplaced, the bridge has to go in the bin.

Some careful drilling and we're ready to shape the bridge. In this case, it's a (relatively) easy job as the original doesn't have a lot of sharp edges to curves that need to be replicated. It's easier to replicate those sweeping lines.

glue acoustic guitar bridge
acoustic guitar custom bridge

Re-attaching the bridge, in this case, means epoxy again. There's a major risk of the bridge sliding about as it's clamped so some very careful preparation was necessary to ensure this didn't happen. Pin-holes and the bolts came in useful in this.

And, you can see the end result in the last image. As it's a nicer piece of rosewood, I think the new bridge actually looks better than the original but, that aside, it's certainly more sound.

So, How Do You Damage A Hole?

Acoustic guitar top repair

Or, more to the point, how do you repair a hole?

Damaging this was the (relatively) easy part: the owner is a 'big hitter'. I've worked on some of his other guitars and, actually, this one isn't bad. We've caught it reasonably early. This guitar is one of the owner's favourites though and he wants to do something before it disintegrates into tonewood-sawdust.

As it happens, we're in luck on this. The majority of the damage is inside the soundhole rosette. This gives us a natural break-line for a repair. It's much easier to affect a discreet patch with that division between the existing soundboard and some newly-added wood.

With that in mind, I figured the best, and least obtrusive, way to manage this was to replace the entire circle of wood inside the rosette.

Cutting cedar to repair acoustic soundboard
soundhole repair acoustic guitar

Using a trammel and my Dremel-type router, I can cut an accurate circle to replace the damaged part from a cedar board. Then, carefully, I remove the damaged wood right up to the rosetted edge and from underneath the fingerboard extension. The fit for the new wood was perfect first time (hurrah). All I needed to do was to square off the edge that butts against the shoulder brace.

Patching acoustic guitar top
fix acoustic guitar soundboard damage

Time for a little support. Effectively, what I'm doing in the photo on the left, above, is 'extending' the soundhole braces to support the new wood. This area contributes hardly anything to the overall tone of the guitar so I'm not worried about altering its sound by adding reinforcement here.

And, speaking of reinforcement, that's what's happening in the photo on the right. Not only will these shaped pieces of wood help to support that newly glued soundhole edge, they will also strengthen it against future, vicious, pick attacks.

Once it's all glued up, I can shape the edge of the soundhole and round it over. That narrow circle of cedar would have been far to delicate to survive my doing that before it was part of the guitar.

Time for finishing. I'm doing something a little unusual here. I've finished this patched-in soundhole with cyanoacrylate (effectively, Super Glue). I wouldn't normally use CA for something like this but, in this case, it will soak into the wood and harden it. This will help it withstand all that pick-punishment in the future. I can tint it to better match the colour and, once built up and cured, it can be buffed to a shine (or in this case, a satin sheen).

Last step is to add a custom-shaped, clear, mylar pickguard to a wider area of the guitar. Again, this will give a little more protection to the top. I've replaced the existing pickguard on top of that to keep the guitar looking original and give one more barrier against future damage.

acoustic guitar repair ireland

acoustic guitar repair ireland