Guitar Body Cracks
Source:Crack & Brace Repair
Top Hairline Crack Repair:
Cracks in spruce tops are some of the most difficult cracks to repair. The reason for this is because of the light wood. Most of the glues that are available today dry with an amber or yellowish color and this shows up immediately on a light Spruce Top.
If the wood has darkened with age, you are lucky and you can use either Titebond or a 2-part epoxy glue for these cracks. If not – you should stick with a bottled hide glue, which drys to a much clear appearance.
Preparation of the Crack for Gluing:
To prevent make a complete mess of the guitar soundboard, some protection is in order.
I prefer to mask-off the crack with painters tape, leaving only about 1/32″ on each side of the crack.
I use the painters masking tape because of it’s easy release qualities on fragile finished tops and vintage instruments.
Place a work light into the sound-hole of the guitar I prefer this LED Work Light with a detachable head for several reasons:
It is small, lightweight, very powerful and will not heat the interior of the guitar causing more problems than you are trying to correct.
Plus the head is detachable for up to 24″ which give you a lot of flexibility for placing the light inside the guitar.
Also get a Mechanics Inspection Mirror, with a extendable handle so you can see the inside of the guitar and keep an eye on the interior of the crack.
Work the Glue Into The Crack:
Take a small dab of glue onto a small artists spatula and start to work the glue into the joint. You can also use your index finger for this as being soft it will more quickly force the glue into the joint.
Now stick your other hand into the sound hole and carefully apply upward pressure to the crack area, opening the crack slightly. This will allow you to get the glue deeper into the crack, more quickly.
Check with the inspection mirror and LED light to see when the glue comes through the crack. Make sure you see glue along the full length of the crack. Release the pressure on the top and hopefully you didn’t change the alignment of the top on either side of the crack.
Glue Clean-Up
Now take a moistened rag and clean the glue off the underside of the top. Clean the rag a few times to make sure you get it all. Do not smear any glue on the surface. Inspect with the mirror and light and repeat as necessary.
On the exterior of the crack, take a clean spatula and run it right down the glue joint. This will spread the majority of glue over the top of the masking tape and we can do a cleanup on the rest of the glue once the glue has cured.
Let The Glue Cure:
We have gone as far as we can with this crack for the day. You should set the guitar aside to dry overnight. The following day you should reinforce the crack to keep it from opening up in the same spot.
Make Your Cross-Patches:
The small little blocks of spruce you will make for the joint reinforcement are called Cross Patches. They are made from small blocks of Spruce. Do not make them thicker than 1/8″ and they should be sized for the area to be fixed.
In more sound producing areas of the top, say the entire lower bout area, they should be somewhat smaller than those used in the upper bout area. Usually for the lower bout I will make diamond-shaped patches about 3/8″ x 1/2″. The grain should run 90 degrees to the top grain and the edges of the patch should be beveled.
Prepare The Area For Gluing:
Sand the underside of the top at the crack area. What I do is place the patch on a piece of 1/4″ masking tape with the glue side up. Spread a little glue on the patch and make sure of your grain orientation – get used to running the length of the grain with the long dimension of the masking tape. Now, with the LED light and mirror in place, position the patch and hold it in place with the tape – this is only temporary however.
Prepare Your Mini Go-Sticks:
I have prepared some 1/8″ dowel sticks in varying lengths, with rubber feet at both ends of the dowels. Use a dowel that is slightly longer than needed and you can position the top of the dowel correctly and slide the bottom across the guitar back – don’t use very much force though as you can open the crack up again – just enough to hold the patch firmly in place. The rubber feet will keep it from sliding around. It works great.
Tip: You can also experiment with smaller bendable rods for this too. I have the tips of a couple of old fishing rods that I have dipped the ends in liquid rubber and these work just like a mini go-board. I’m sure there are other materials you could use like bamboo or carbon fiber. Let me know if you come up with something.
Finishing:
We will cover the proper way to finish the crack repair area in the article Finishing Crack Repairs, since there are so many different kinds of cracks to address.
Tags: closed guitar crack repair, fixing cracks, guitar top crack repair, guitar top hairline crack repair, how to fix a guitar crack
March 13th, 2010 at 4:28 pm
Great tips and photos. You obviously know your stuff and it shows. I am an instrumental acoustic and electric guitarists who writes his own music, and of course, the “health” of the guitar itself is essential. ( http://timhillwood.com )
I also have a good friend that’s getting quite good at guitar repair himself, and I’ll pass on your website to him now while I’m thinking about it.
I wish you the very best and thanks for keeping the source of the music alive and well. It takes special skills and practice to do that well.
March 15th, 2010 at 8:53 pm
Thanks Tim, look for continued content in future articles. I will be covering lots of subjects, from simple fixes to major repair jobs.
David