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

I recently had to do some work on a guitar made from High-Pressure Laminate and I thought the merits and drawbacks of that material might be worth discussing. I’ll also touch on the repair I did to illustrate things.

Before I start though, this is not a discussion of tone. If we start down that road, I’ll be here for the next year, refereeing arguments between the warring factions. If you want to talk tone, there are plenty of forums where you can do that until every single cow has come home. Go nuts.

 

The Pros and Cons of HPL use in guitar building and repair

 

So what is High-Pressure Laminate?

Well, to be honest, I have to come clean at this point. While I know a little bit about wood I don’t know a heck of a lot about HPLs (High-Pressure Laminates).

That said, I’ll try to summarise what I know and — I think — what you need to know*.

HPLs are made from a number of laminations or layers of what is, essentially, paper. It’s slightly different to the paper we use every day but, for all intents and purposes, it’s paper.

There’s generally an overlay layer, sitting over a ‘decorative’ layer (more on this in a sec), and then one or more layers of a stronger paper.

High-Pressure Laminate HPL construction example

These layers are impregnated with a phenolic resin and are heated while simultaneously being pressed at up to 2000 pounds of pressure per square inch

The result is a thin sheet that’s very hard and very tough.

For an everyday example of HPL, chances are your kitchen counter tops are covered with a HPL material. Formica is one, well-known, brand of HPL.

*Actually, I lied — you probably didn’t need to know the ’sciency’ bit but I reckoned it would be useful as we went on. The following stuff, you probably do need.

What do kitchen counters have to do with guitars?

More guitar builders are making instruments using materials other than wood. Martin Guitars, for instance, have widely embraced HPL materials and offer a number of models where some — or even all — of the back, sides, or top are made from HPL.

While a Spinal Tap None-More-Black colour is popular, HPLs for guitar use will often have a wood-grain pattern printed onto that ‘decorative’ layer we mentioned earlier. The overlay layer can also be textured to feel a little more ‘woody’ if the builder wants to play that up a bit.

The pros of HPL

So what are the good points?

Manufacturing

Well, from a manufacturing point of view, working with HPLs is likely much more consistent and predictable. It’s almost certainly considerably cheaper, from a materials and an assembly point of view too. Full disclaimer: I don’t know either of these things for sure but I reckon it’s a safe bet. Happy to be corrected.

This manufacturing saving means you can often buy a HPL guitar more cheaply than its wood stablemates.

As a slight aside, from a wider manufacturing point of view, the move to more sustainable guitar materials is well underway and we, as players, will have to get used to it. For many reasons, wood will become less-used in musical instruments. While many will decry this, there’s very little they can do so, it seems sensible to make peace with it.

If you’re a wood purist, that’s cool, but you’ll probably have to get used to paying more for your instruments and understanding that those instruments may come with restrictions. But back to the main story…

For the player

“I don’t care about how easy or hard it is to build a guitar,” you cry, “what’s in it for me?”

Well, HPL isn’t subject to the same whims and idiosyncrasies of wood. If you live somewhere where the environment hates guitars, this is a godsend. Very wet and very dry environments will hold less danger for the HPL instrument.

Within reason, a HPL instrument can get wet without too much hassle. The surface is super hard and it will laugh at scratches, pick-wear, etc. It will handle heat better than a wooden instrument.

There’s no actual ‘finish’ so there’s nothing to crack, or check if it gets too cold. You can probably pour a selection of household chemicals over it without any damage (although I’d probably still try to avoid that — for many reasons).

If you want a guitar to drag around without worrying too much about scratches, or rain, or heat, or humidity, or dryness, these instruments could be just the ticket. Obviously, this isn’t an invitation to stress-test a guitar to destruction but HPL guitars should hold up to environmental hassles better than an instrument made from a dead tree.

The cons

So what’s the problem with this wonder material? Well, other than the ‘not-wood’ issue that bugs traditionalists, there are two main problems.

Hardness as a weakness

The first is that, while HPL is incredibly tough in one sense — you won’t scratch it, or soak it, or all of the other things listed above, but…

It’s hardness makes it somewhat brittle.

When it’s bonded to a kitchen counter, that’s not so much of a problem but, when it’s made into a guitar shape, and dragged around the world by musicians, a good whack in the wrong place/direction and you can end up with a heap of shattered HPL pieces.

And shatter is a good term.

You'll be left with jagged, irregular shards of material that resemble a guitar jigsaw.

And that brings me to the second problem.

It’s not terribly repairable

HPL (at least in guitars) is not really made with repair in mind.

Now, let’s face it: if you whack your wooden guitar, you may well break it too.

Buuuuuut… The nature of that instrument lends itself more readily to repair. The sides, top, and back are generally thicker and can be more easily glued (and wood glues are typically friendlier and more forgiving to work with). Wood itself can be shaped, and formed, and bent. Dings and dents can sometimes be lessened or removed altogether. And, since most wood-built instruments have a finish of some kind, evidence of repairs can often be hidden or minimised.

We get none of that with HPL.

The material is usually very thin and difficult to butt against neighbouring pieces. Not that that matters because, if HPL does break or shatter, the laminations will often break ‘separately’. That is, different layers will break in slightly different places and in irregular ways. Fitting shattered HPL back together can sometimes be impossible.

Exaggerated example of how HPL laminations can shatter 'separetely'

To show what I mean, the image above illustrates (and exagerates) the way different layers/laminations can break differently. Imagine that happening with all those layers sandwiched together and you have some idea of the problem.

Compounding the repair hassles, even if you can make some attempt at reassembling your jigsaw, it won’t ‘support’ itself.

In the photo below, for instance, I had to bend a piece of mahogany to act as a ‘former’ inside the guitar side. I glued this shaped piece to the inside of the guitar side and built my jigsaw on top of it. Similar story for the back section.

I've had to bend some wood to glue to the sides. This will act as a 'former' or support to glue the HPL pieces onto.

And, when working with HPL, lovely friendly wood glues are out. I’ve read of repairers using CA (cyanoacrylate — super glue) but, to me, that’s never felt the right choice for this job. So, epoxy is the order of the day and that is — not to mince words — a pain in the ass.

Lastly, forget about minimising the signs of a repair. Quite the opposite. There’s no finish to provide some camouflage and, because it’s so incredibly difficult to get shattered HPL pieces to mate nicely, there’ll be high and low spots that have to be flattened down. That probably means you’ll sand through the overlay, and even the ‘grain’ layers, so it’s going to look ugly as sin.

HPL repairs are the Frankenstein’s monsters of the guitar world.

Oh, man, that's not pretty. Don't look at me. Don't look at me!!!

Seriously. Do you think I like showing you this photo? Even though I made it incredibly clear before I started, do you think I liked handing that back to a player? I’m an uptight perfectionist and it makes me very, very sad that this is the best I can do with this guitar.

Because it’s almost impossible to make a good job of HPL repair (and because, let’s face it, nobody likes paying for something that’s not a good job), I often turn away HPL repair. This one was a special case.

Many other repairers are in the same boat. It's a lot of messy, fiddly work, which means it's not cheap. And it's a tough to hand over a scarred mess and take money with a clear conscience (even if you feel you've done the best possible).

The bottom line

HPL guitars have a lot of advantages. Seriously. Despite my whinging, I think they have a lot going for them and no one should disregard them. As well as their toughness merits, it can be a more affordable way to buy an instrument (or buy into a more expensive brand).

I’ve seen heaps of Martin HPL guitars, for instance, and they’ve all been well made, nicely playing, good sounding instruments. You do yourself a disservice if you discount them through snobbishness.

However, go into this with your eyes open. Bear in mind the potential risk should the worst happen.

And, if you do end up with a heap of jagged guitar-jigsaw pieces, be aware that repair will probably be very difficult. If you can find a repairer to take it on, cut him or her some slack. They’ll be attempting the almost-impossible.

I hope this hasn’t been too much of a downer. I think it’s good to be informed, though. Hope that’s ok.

Shout out in the comments if you've questions or, you know, comments (just not about tone 😉)


By the way, HPL is a relatively new guitar material and I freely admit I may be missing something. I know there are a lot of repairers that read these articles so, if you have some solution or improved method that I’m missing, please drop me a line and let me know. I’ll update this screed and will sing your praises to all who’ll listen.

UPDATE: Email subscribers came thorough with some suggestions. Mailing list FTW!.

Thank you to Gary, Frank, Martin, Bill, Bill (2), Mike, Stephen, and Bradley who came at this from an auto/boat repair viewpoint and suggested fibreglass as a repair method. From my experience of HPL guitars (and my inexperience of fibreglass), I'm a little unsure but it's certainly food for thought and possible experimentation.

Thanks also to Wade, Shane, Mark, and Steve for pointing out SeamFil, which is a product specifically for filling chips in HPL. For smaller HPL repairs, this is certainly useful. Cheers.

And lastly, thanks to those who were kind enough to email to say nice things, or just to commiserate 😉