Sometimes guitars are damaged due to bumps and knocks, and other times humidity and dryness can cause wood and glued surfaces to crack.
Cracks
One of the most common repairs on steel string acoustic guitars is soundboard crack fixing. The most common cause of soundboard cracks is dryness and inadequate humidification. Subjecting an instrument to extremes in temperature can often accelerate any problems due to shrinking and dryness.
* Please keep your guitars humidified properly. The best type of humidifier has a large sponge reservoir and fits inside the soundhole suspended by the strings and allows moisture into all areas of the case. Don’t forget, fingerboards dry out, too, and should be oiled once or twice per year to prevent shrinkage.
A wide crack was one of 5 in this acoustic guitar top.
Cracks can usually be repaired well with a combination of gluing, clamping, and the addition of small 4 x 9 mm cleats. A well repaired crack will be as strong or stronger than the original wood and should restore the full tone and volume of the instrument.