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What should i do to fix an 1" crack (very tight) on the back of my guitar . Please help , i have to do it myself .

I just bought an acoustic guitar , with a solid mahogany back (arched).

i accidentally hit the armrest of my chair with the back of my guitar . My guitar crack for about 1inch (2centimets) at the back . The crack look very tight on the outside , and i dont see any crack from the inside of the guitar . As you can see in the pictures

i do some research with google and i think i should glue the crack with Titebone glue and add cleats to fix it . But i'm not sure if the glue can flow into the crack . And should i add some cleats to the inside ? its hard to me to find the location of the crack from the inside thou .

i cant find a pro luthier at my country so please help me out . I'm sorry for my english is very bad .

here is the pictures :

*the metal piece to point the location of the crack

Tags: crack, fix

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You can drip naphtha into the crack on the outside of the guitar and then look inside the guitar for the wet spot... to see if the crack goes all the way through.  It's a good visual indicator but I usually will only get out the glue at least a couple of hours later being a little concerned that the naphtha needs to be completely evaporated before getting out the Titebond glue.

IMO this is a crack that could or could not have a cleat.  It's not a high stress area, we know why it cracked, you banged it on the arm rest, and the crack is naturally closed at rest.  A cleat would not hurt either and it's super easy to add one little cleat.  I would favor adding a cleat.

To get glue in the crack wash your hands first, seriously, the glue will pick-up any dirt on your fingers and forever embed it in the crack if your hands are dirty.  On spruce tops this is super important....

With a hand in the guitar pump the crack from the inside with your fingers while rubbing glue in from the outside.  Pumping the crack from the inside will assist the glue in wicking into the crack.  the goal is to see little, tiny beads of Titebond on the inside and then you know that you used enough glue.

There is the issue of getting things level too.  I suspect that this crack is naturally level when closed as it is.  If this is correct no worries about leveling it.  If it is unlevel or may be unlevel when glued magnets, rare earth magnets, a clear semi-rigid caul (plexiglass) and waxed paper to avoid gluing the caul and magnets can level a crack while the Titebond dries.

By the way what country are you from and welcome to the forum.

Hi Gbot,

What Hesh said, and if the crack turns out to be superficial or just tight and not "opening" you may wish to dampen the crack just before you rub the Titebond into the crack. Flexing the back back and forth will help the diluted Titebond to seep into the crack and also help it flow into the adjacent wood fibre on the sides of the crack. Leave a little excess glue on top of the crack as it will (probably) suck into the crack as it dries 

This crack is unlikely to prove damaging to the guitar structure or tone, but after you rub some glue in and wipe of the dry glue excess with a soft cotton or terry rag, just keep an eye on it and if it get bigger over a couple of months give us another call.

Good luck with this,

Rusty.

Do you know what type of finish is on your guitar? Lacquer? Polyurethane?

You might have one of the few situations where extremely thin superglue (Cyanoacrylate) is a good solution.

Not common hardware store Cyanoacrylate glue. A type that would likely need to be ordered thought the mail.

Your English is perfectly clear.

thank you very much for your reply , David .

The finish work on the back of my guitar is very thin , its almost look like and feel like natual wood ,

i think i need a liquid glue that can flow into this tight crack . 

Thank you very much for reply . is it ok for me to dampen the crack with water ? the crack is very tight so i think if the water took place inside the crack , the glue will not able get in .

thanks for telling me that the crack do not do any damage to the tone . this is very importal .

thank you very much for reply . I was try to massage the crack after it happen but both edges of the crack is not moving at all , it's almost just like a scratch . Thats why i dont know if the glue can get in .

I'm from Vietnam , i'm not living in the capital so its hard to me to find a professor luthier , and if i do found one , i still have to travel about 5hours on car to arrive .

I think the idea of testing to see if a crack goes all the way through is mostly unnecessary.  Cracks almost never go only part of the way through a piece of wood that thin.

But the good news is that this is a very minor crack, and is in a location where it is not likely to spread because stress in the area is contained by the guitar's sides.  You will not do any harm by doing nothing and just looking at it occasionally to see if it is spreading.

Nothing wrong with your English, by the way.

Thank you very much for reply .

i want to wait and see if the crack getting bad or not becouse right now i dont really think i can get the glue in to that crack . But i heard people said that the solid wood of the guitar can easily get dry and crack by low humidity .

And if i let this crack the way it be , will it do any harm to the tone or sound of the guitar .

I'm bad at writting english becouse i've only learn it on the internet , i'm try to write it simple as possible . i can understand what other people said .

I think you are very clear in your English although it would be helpful to know your location and native language. This forum has international members who may can assist you much better than we Gringos can.

Leaving the crack unrepaired is risky because dry air causes shrinking with tops and backs. The tone of the guitar will not be changed. My main guitar when young had a similar crack and I kept a Bandaid adhesive bandage covering it until I sold it. Knowing what I know now, I would repair the crack if I could as it will collect skin grease and dirt every time you rub it to check it (and I know you have already done this a hunded times :') ). The crack edges can chip and get caught on your clothing making a tight join very difficult later.  Alphatic Resin (AR) and Poly Vinyl Alcohol (PVA) type glues can be thinned ~1part water+9parts glue and still do the job for this repair if you don't trust it will penetrate undiluted. With the thin wood used here, you will not have a problem with the standard glue or thinned glue penetrating this crack. If you don't want to do the pumping Hesh suggested above, I would just rub the glue into the crack for a few minutes. The pressure of your fingertips will do the job. Just leaving the glue on the surface of the crack may work but I wouldn't trust it.

Should you decide to repair it I suggest the folowing:

First try to clean out the skin oil and dirt out of the crack from rubbing your fingers on it. I use a white paper towel dampend with isopropyl alcohol or Naptha or cigarette lighter fluid and gently press (don't rub) the crack with it 4-5 times. You need to use something which leaves no residue which might interfere with the glue bond. Allow to dry a few hours.

Because it might be difficult to apply a small enough amount of Cyanoacrylate (CA or superglue) and the resulting difficulty of removing the excess without smearing it, I would strongly suggest following Hesh's instructions and use a PVA or AR type wood glue  These are the glues used in general woodworking, craft projects and children's school art projects. In the US and elsewhere they are sold as Titebond wood glues or Elmer's wood glue. You may find other brands and honestly they are all pretty standard.  Any of those will work fine for this situation. They are creamy white or pale yellow opaque in the bottle and when dry they become clear to light brown. They are sold at hardware, super markets, craft and office supply stores and only ~1ml is needed for this so get the smallest/least expensive container you can find. Be sure to clean any exterior squeezeout or glue smears well within a few minutes with a wet paper towel a few times with a clean area of the paper towel each time before the glue dries. On the inside surface of the crack, wait for any squeezout to turn rubbery (~ 1 hour) before trying to remove the glue. Use a fingernail or tweezers or a knife to remove these 'boogers' and there will be no evidence of the repair. Hide glue, Fish glue or Bone glue would also work for this if prepared and applied properly. Stay away from all polyurethane glues (Gorilla Glue, Construction glue, etc). They are very messy and/or foam while curing and impossible to clean and hide once dry. 

Good luck with your new 'baby' and let us know what happens!

Mark Fogleman

Cedar Springs Creative Workshop

Concord, NC

Thank you so much for valuable suggestions . With this instruction , now i know what i should do to fix the crack .

i'm from Vietnam and its may take few days to order and ship the Titebond I glue from the capital , its hard to find in the town where i'm living now . i don't want to use other glue becouse something may go wrong if i pick the wrong type of glue .

i will be very careful from now on . i've been playing electric guitar for 7 years , this guitar may count as my first acoustic guitar . Becouse i'm too familiar with the weight of the electic guitar , everytime i pick up or moving the acoustic guitar i'm always using too much strength . i really appreciate everyone help . Have a good day !

Good luck with your fix. I'm sure it will be fine.

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