Re-hydrated crack too tight to get glue in ...

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simonm
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Re-hydrated crack too tight to get glue in ...

Post by simonm » Tue Feb 21, 2017 2:47 am

Assume you have a guitar with a cracked top due to humidity issues (winter, central heating, icy weather, the white stuff on the ground etc). After humidifying for a few days the crack is almost visible and as tight as a tight thing. Do you have a strategy for getting glue in? Would cleating alone be enough? Do you ever put some hhg into the crack before humidifying?

I have had two guitar with top cracks due to drops in humidity (20% in a climate where 50%-70%-ish is the norm). In both cases rehydration closed the gaps (initially 1mm-2mm) so tight that even knowing where the crack is it is hard to find. One was a 1980's Spanish for a well know maker in my own place. The other was one of my creations and at a customers house. Jan/Feb seems to be the peak humidity caused top crack time based on a massive sample of 2 guitars.

My attempt at gluing involved rubbing in fairly thin hhg from the top while manipulating the top with the other hand through the sound hole. To complicated matters the crack is very close to the centre fan brace so at one end next to no space for cleats.

Any thoughts?

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Allen
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Re: Re-hydrated crack too tight to get glue in ...

Post by Allen » Tue Feb 21, 2017 7:04 am

I've only had to do one of these type of repairs, and that was on a tenor uke.

I used thinned out HHG and massaged it into the crack from the top and manupulated the soundboard as best I could from underneath. Could just barely reach it through the sound hole. Once I was certain that some of the glue had penetrated through I added some full strenght glue and continued in the hope that it would get pulled in as well.

Seemed to work and repair was invisible.
Allen R. McFarlen
https://www.brguitars.com
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simso
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Location: Perth WA

Re: Re-hydrated crack too tight to get glue in ...

Post by simso » Tue Feb 21, 2017 3:12 pm

On a nice tight crack that has closed up from humidying, I have two ways of doing it.

First put a small scissor jack inside and re-open the crack, pack it with glue and then let remove the jack, it will pull up just fine.

If using a jack and it does not open up enough, I apply titebond to the surface of the crack and use air pressure 15 psi to push it in, clean up and allow to dry

Steve
Steve
Master of nothing,

Do your own repairs - http://www.mirwa.com.au/How_to_Series.html

simonm
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Re: Re-hydrated crack too tight to get glue in ...

Post by simonm » Tue Feb 21, 2017 9:40 pm

Thanks guys.

The sissor jack is a new concept for me. Had a look at it over on stewmac. I have to admit I would be quite nervous cranking that up inside a lightly build guitar for the first time. I do have stewmac voucher at the moment. Hmmm

Simon

simso
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Joined: Mon Apr 25, 2011 10:36 pm
Location: Perth WA

Re: Re-hydrated crack too tight to get glue in ...

Post by simso » Wed Feb 22, 2017 2:01 pm

simso wrote:On a nice tight crack that has closed up from humidying, I have two ways of doing it.

First put a small scissor jack inside and re-open the crack, pack it with glue and then let remove the jack, it will pull up just fine.

If using a jack and it does not open up enough, I apply titebond to the surface of the crack and use air pressure 15 psi to push it in, clean up and allow to dry

Steve
Had to glue a split laminate up the other day, heres a link showing how I use the air pressure trick.

Steve

http://mirwa.com.au/HTS_Repair_Split_Laminate.html
Steve
Master of nothing,

Do your own repairs - http://www.mirwa.com.au/How_to_Series.html

simonm
Blackwood
Posts: 176
Joined: Mon Sep 07, 2009 7:09 am

Re: Re-hydrated crack too tight to get glue in ...

Post by simonm » Thu Feb 23, 2017 4:36 am

Thanks Steve.

Very interesting method. Thanks for linking it in here.

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