High temperatures can cause cracking, make glued joints and tops lift up and buckle, trigger neck warping, and a host of other problems. The least severe of these issues can be corrected by a good luthier via a set-up, neck adjustment or the careful re-application of glue. But summer has been the killer of many, many fine guitars.
Two basic cautionary points:
• Never leave a guitar in your car’s trunk: Temperatures in the trunk can be up to 60 degrees hotter than outside, which means that if you’re in the South and Southwest, it could be rocking 160 to 170 degrees in there during peak summer temperatures. Even a few hours can cause bridges to loosen, necks to leave alignment, frets to rise and other issues. Changes in temperature not only affect acoustic guitars, but electrics, too. Besides neck warping and fret heave, electric guitar finishes exposed to contrasts in heat and cold will crack, due to expansion and contraction.
• Use hard shell cases for summer travel: Sure, gig bags are a practical and comfortable way to carry guitars, but a hard shell case offers more resistance to environmental dangers including heat. And many soft bags are made of vinyl and other plastic-resin derived material, which, in fact, absorb heat and retain it, essentially putting you guitar in a sweatbox.
Also, keep your guitars out of direct sunlight as much as possible, which can be challenging during outdoor gigs. Always place your guitar stand in the shade. Besides the finish damage direct sun can cause, overheated guitar strings will stretch when they’re struck and you’ll drive yourself nuts trying to stay in turn while you play. Repeated exposure to the sun bleaches finishes quickly. It’s also more important to wipe down a guitar’s surfaces after playing during the summer for the simple reason that you’ll be sweating more, and human sweat left on a guitar can destroy necks, frets, bridges and other hardware, as well as damage finishes and make the fretboard a gunk-covered mess.
The most important consideration is keeping your guitar safe during the summer in very low or high humidity. Low humidity is the biggest enemy of guitars, especially acoustics. If you’re touring, be aware of the relative humidity or RH levels of the regions you’re playing. In the U.S. the Rocky Mountain area, Montana, Wyoming, Nevada and Arizona all have very low relative humidity year ’round, which, when combined with high heat, can be extremely rough on acoustic guitar tops, side and backs, and all guitar necks, causing a host of problems, but primarily cracking and warping, and, with prolonged dryness, a susceptibility to fractures. Commercial sound hole and guitar case humidifiers are available. There’s also a DIY version. Dampen a sponge, put it in a plastic sandwich bag, and make a few small holes in one side of the bag. Then lay the bag with the damp — not soaking — sponge inside the case with the holes facing up. Refresh the sponge when it begins to dry.
High humidity is especially rough on solid-body guitars. States with high RH ratings in the summer, like Florida, Louisiana and Alabama — as well as, thanks to climate change, locations along the Eastern Seaboard — are the major trouble spots. Small bags of silica gel placed within guitar cases will help. But the best solution is to keep your guitars in a temperature-controlled environment, like an air conditioned home, hotel room or vehicle, as much as possible.
Too much humidity can cause the tops of solid body guitars to swell, creating high action, and can alter an instrument’s tone. If the swelling is allowed to continue unabated, the binding and glue joints can separate from the guitar’s body. Watch for any slight warping on your six-string’s surfaces. If you notice warped spots, get the guitar to a safe environment or, if swelling doesn’t cease, consult a luthier as soon as possible.