Every acoustic guitar owner eventually accepts that scratches and dents and scratches are impossible to avoid. Even the most careful owners will accidentally bump their acoustic into something from time to time. Thankfully, damage is most often done to the finish of the acoustic guitar, which can be easily repaired. Dents are another common mark on acoustic guitars. Unfortunately, most people do not know what to do if they see a dent on their guitar.
Many people who find a dent immediately go out and buy wood filler or a device to help pop the dent out. This is completely unnecessary because the problem can be solved simply by using water. All you need to do is place a small drop of water onto the dent. The wood underneath the dent will absorb the droplet and swell up, pushing the dent out to its original position. It will look like the guitar never even had a dent. This technique only words for dents and should not be attempted on a chip or a crack. There is not a particular length of time that you should leave the water on the dent. Try leaving the water on the dent for a minute, then wiping it off and waiting to see how the wood reacts. Apply water again if necessary.
When people find a scratch on their guitar, their first reaction is to sand the wood around the scratch. This is usually successful at levelling out the wood and making the scratch disappear, but it will make quite a mess. Applying shellac is the perfect solution to get rid of a scratch. Some people mistake shellac for varnish and the end results look very similar, but there is a big difference between the two. When varnish is applied it soaks into the wood, while shellac creates an outer coating on top of the wood. Shellac is so much better at getting rid of scratches on an acoustic guitar.
Unfortunately, shellac is normally sold in large volumes and you only need a small amount to cover the scratch. If you want to save some money, try using clear nail polish as an alternative to shellac. Most people tell you to buy varnish, but shellac is much more versatile and better for touching up an acoustic guitar.