Wood is hygroscopic, meaning the moisture content of the wood is subject to change based on the relative humidity. In simple terms, this means the cells of the timber can either expand or contract based on the amount of moisture in the air.

In the case of unfinished guitars, almost all problems associated with humidity will be due to the wood contracting due to reduced moisture content in the wood. This can result in both problems listed below:

Cracking or a separation of the wood pieces the body is built from

A loose-fitting neck pocket

Humidity also affects finished electric guitars, especially with regard to tuning stability and intonation, along with potentially raising the action due to changes to the neck profile. These are normally addressed by adjusting the individual saddles and truss rod. 

The most effective way to prevent this problem from occurring is to keep your guitar in a hard case and/or use some form of humidity control in the room your guitar is kept in, or the case itself. There are a number of products available for both purposes.

Right, now that we know what we are dealing with, let’s take a look at the most common problem associated with changes in humidity and the most visual, cracking.

Repairing cracks or separation

All of the guitars at www.xuqiumusic.com (and almost every other guitar kit retailer for that matter) are manufactured in Shandong, China which has a monsoon-influenced, four-season humid continental climate, with hot, humid summers, and cold but dry winters.

The humidity level in Shandong, China

 If a guitar made in an environment that has a relative humidity of 65% is delivered to a desert region such as Las Vegas which experiences relative humidity levels as low as 8% the hygroscopic nature of wood means it is going to lose moisture. This causes the cells in the wood to contract, raising the potential for small cracks to appear. 

The humidity level in Las Vegas, NV, USA

This kind of damage is more likely to occur on the guitar's body, as the body is built from 2 to 3 different sections of wood, and despite being of the same species are likely to have different tensile strengths. These opposing forces can result in cracks occurring anywhere on the body of the guitar but speaking from experience they mostly occur toward the lower bout of the guitar. 

crack on guitar kit body

In most cases, the crack will be minor in nature, but in some cases, the crack will be much deeper. In either case, the steps below will help you address it.

1. Identify the problem

We first need to identify exactly what we are trying to repair. For example, is it a genuine crack? Or have the different sections of the body separated? Does the crack go right through the body of the guitar?

For example, if the crack extends right through the body we’ll need to address both the top and underside of the guitar, and the guitar will need to be clamped. 

2. Acquire the right products

When repairing cracks I recommend using CA (Cyanoacrylate Adhesive) glue, aka superglue. However, aim for a water-thin version such as this will more easily infiltrate the crack. 

You can also apply a tinted wood fill epoxy such as this if the crack is  rium moisture content, meaning it matches the moisture content of the surrounding air.

You will also require a putty knife if using epoxy and sandpaper in both medium and light grades and a wood clamp or similar tool to fix the body of the guitar in place (If you don’t have a clamp don’t worry, we’ll cover this shortly) if the crack is deep.

3. Cleaning out the crack

The first step is to remove any dust or grit within the crack and surrounding area. A simple way to do this is to run a scalpel blade back and forth along the crack, removing any grit and residue and then wipe down with a very small amount of warm soapy water.

4. Fill the crack

If using epoxy, use a putty knife to work the epoxy into the crack. Remember in some cases epoxy comes unmixed, the hardener is separated to the middle of the roll. You will need to mix it around in your hands before applying so be sure to wear gloves.

If using CA glue fill the crack with sawdust from the guitar itself (if possible) as this will match the body. Identify any areas that will require sanding and use medium grade paper sand the area until you have a small amount of sawdust to work with.