Guitar repair – The belly bulge: whys and wherefores?

Happy New Year, folks! I’m back!

Of late, I have had to tend to a slew of belly bulge cases. I hope to replicate for you all the explanation of the whys and wherefores that I usually give guitar owners.


What is a belly bulge?

A belly bulge is said to have occurred in an acoustic guitar when the area of its top behind the bridge – towards the end block – swells up and rises. Try and imagine: the strings are pulling that portion of the top towards the headstock and along comes the belly bulge aiding the strings. As a consequence of the ‘double strain’, it is not uncommon to find that the bridge gets twisted out of shape.

Also, in keeping with Newton’s Third Law of Motion, the equal and opposite reaction to the belly bulge, the areas alongside the soundhole are forced to sink.

What these three things do together, is force the action of the guitar up to unplayable levels. If the instrument is kept under the continued strain of tensioned strings, the problem is bound to compound, the least of which is the bridge pulling up too.


What causes a belly bulge?

There are a few reasons for your guitar beginning to sport a belly. The first among these is an

  • Inadequately sized or inappropriate material bridgeplate

The bridgeplate is the heart of your instrument and its job is to counter the pull of the strings and lend stability to the top. If it is small in size, it won’t be able to do its job properly. In fact, it is quite likely that it will suffer a similar fate like the one in the above photograph. Think of a six-foot man with a small heart. The poor heart may be overworked and will fail at some point.

Also, if the bridgeplate is of inappropriate material, it will fail sooner rather than later. In India, mid-segment guitars – even those manufactured by a big Japanese name – bridgeplates of inappropriate material is a common problem. This is because manufacturers wish to cut manufacturing costs and increase profit margins as much as they can. And so, they fashion bridgeplates out of whatever wood they they first lay hands on.

Within a few months of purchase, such instruments start sporting a belly, and from then on, the problem only multiplies.

What you want to see is a bridgeplate made of a hard wood – rosewood, mahogany, walnut, padauk, and maybe, maple – that is capable of soaking the pressure of the strings, remain stable and keep the top stable too.

The photograph below shows the position of the bridgeplate, gives an idea of the correct size, as also its material. From the looks of it, this seems to be a healthy, rosewood bridgeplate.

  • Inappropriate string size

If you buy a proper guitar from a brand name, you can be assured that either in the owner’s manual or on the internet, you’ll find the specifications of your instrument. Among the specifications, you’ll find the prescribed string gauge for that particular model. Now, you can easily go a gauge higher or a gauge lower, but no more and no less.

Medium strings on orchestra models (OMs) or parlour guitars will wreck the instrument and XL strings on Dreadnought/Jumbo  models will never be able to evoke the same kind of response from the instrument, which it is capable of giving.


  • Leaving strings tensioned for long

Leaving the strings under tension for a long time (a month or more) is the single most destructive thing you can do to your acoustic guitar. It affects all the joints of the guitar, right from the headstock to the end block, and affects the bridge area – which bears the maximum strain – the most.

The bridge and the bridgeplate resist the string tension to a certain point after which they give up and from that point a belly steadily forming can easily be noticed.


  • Cracked/broken/loose braces

The bracing on the underside of the top of your guitar is there to support the soft wood (spruce, cedar), in the absence of which the top would immediately distort and collapse under string tension.

In case any of the braces get loose/broken/cracked, they become incapable of doing the job that they were meant to do. Unless the faulty brace is fixed quickly, there is a belly bulge coming soon.


Tackling a belly bulge

Here, I feel it pertinent to record that ALL acoustic guitars – irrespective of brand and size – will develop a belly over time. However, while a guitar costing Rs 1,00,000 ($1200) will develop a belly in some 1.5 – 2 decades, a Rs 10,000 ($120) guitar may develop it in a matter of few months. Also, while the belly in the former may be slight, the belly in the latter may be enough to require intervention.   


  • The rap exercise

In a bid to rule out a problem with the braces, it is advised that you hold up your guitar to your ear and rap the top at various spots on the top and the back with the fleshiest part of your fingertips. If you hear a second sound, an ‘echo’ of the rap, it means the brace nearest to the spot of the rap is either broken, or loose. If all other factors are normal, rectifying the brace may arrest the development of the belly.

(And for that I am at your service)!!!!!!!!!  

Watching the string tension – tuning down your instrument half a step or a full step – when you know you will not be playing it for a month or more, goes a long way in maintaining the health of your guitar.






Amit Newton

An experienced guitar tech with over 10 years of experience working on acoustic Gibsons and Martins in the Gulf region. There is nothing that cannot be repaired; the only consideration is the price at which it comes. And yet, if there is sentiment attached, no price is too high! WhatsApp/Call me: 7080475556 email me:

3 thoughts to “Guitar repair – The belly bulge: whys and wherefores?”

  1. Same case with my guitar of big brand Japanese company model F310. As I asked in other post can we stick a new stronger bridge plate of harder wood on top of existing one i know tone will not be same, but will it be playable. I am currently using jig of two 2/4 wood with wong nuts to use as a clamp on belly. Also i am using .12-.53 . What gauge would you suggest based on my scenario. Action is about 4mm on 12th fret. Tuning down guitar seems to reduce the belly a bit.

    1. Hi Mudit!
      First, apologies for missing your comment altogether, and thus, the late reply.
      If you search F310 or Yamaha in my blogposts you will find a gazillion posts about what a crappy guitar this is.
      You know what is worse? F280!!!!
      Now getting to your problem, the jig may help you, if – a) you wet the bridgeplate and then clamp it for a continued 3 days, or more.
      Lighter strings will help in not letting the belly return in a hurry (say, 10 – 47).
      However, do not remain too hopeful. I would suggest that you start saving money and start looking for a guitar in the range of Rs 12 – 15K.
      If you can afford to buy a more expensive guitar, all the better for you.
      Hope that helps!

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