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I glued a mahogany back together a while back and had to put it aside to do some other house projects, and when I came back to get going again a couple days ago the unbraced back had curled a little. No sweat, I dampened the concave side and put it on a plastic sheet and put a 1/8 inch steel plate over it to flatten it. This morning when I pulled the piece out, there was mold all on the dampened side (now dry), about a square foot of mold in two areas. I've started sanding this out and will scrape it and alcohol it, but my experience is that once mold is in wood it is there for good just waiting for the right conditions to blossom again.

What's my plan? Is there something that really works on mold? Start new pieces? Move to another house?

thanks - Mark

Clorox will kill mold. First scrape the mold off along with a bit of the wood. Then mix 1 part of household clorox with 4 parts water and sponge it onto the wood. Then let dry. The mold should not come back unless you get it soaking wet again and incubate it for a few days.

I have used Clorox, but now use 20Volume Hydrogen Peroxide that hair dressers use for bleaching hair. Stronger than Clorox and quicker.

Bob

Thanks for the advice here. I already did the clorox thing and put it up under a steel plate (separated by saran wrap) for a couple or three days.
1A
So the mold thing happens commonly? I've wondered why guitars aren't finished or sealed inside. That would help keep mold spores from sprouting into moldy blackness

Your technique was incorrect. Don't apply the clorox and then cover the wood, leaving it wet. That will just encourage more mold growth. Get the wood dry as fast as possible and keep it dry. And if you keep the guitar out of excessively humid environments (less than 60% RH) you should not have any further mold growth.

Actually the mold thing is not something that happens very often and this may be the first post on this forum about it.

This leaves me to believe that you are not using humidity control where you build or store your in-progress work. Humidity control is an absolute must with guitar building and if not observed any resulting instruments will likely not survive the changing of the seasons without cracking or deformation.

For Lutherie for most climates a range of relative humidity of 42 - 48% works well for many of us and the major f*ctories too. If the guitar will live in a very dry or a very humid climate once complete these numbers can be tweaked some as well.

How you measure the RH (relative humidity) is a discussion in and of itself too because the vast majority of store bought hygrometers are simply junk and no better than painting 45% on your wall and going by that.... But that's another subject and there is lots in the OLF archives about hygrometers and which ones suck and the few that don't.

Regarding sealing the inside of an instrument there are two sides to the argument here but as a repair guy who also built as well I'm not keen to seal the insides. First regardless of what you use to seal, shellac, etc. it will only belay and delay the permeation of moisture for likely a couple of hours tops.... The down side is the serviceability argument. If the thing needs to be repaired in time the presence of shellac makes it more difficult to repair without removing the shellac so that the glue used has some unadulterated wood to grab onto. Some builders seal the insides any way and lots of repair folks when they have to deal with their stuff are known to use colorful and descriptive language....

how thick was the set?
mike

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Mike Collins

Just a little over an eighth - maybe 5/32

be careful to not use too strong of a bleach... you don't want to end up bleaching the wood!

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I've seen mold inside old guitars left in flooded basements but never heard of it in a shop setting. What does it look like? If it is indeed mold then I have to agree with Hesh and suggest that you have bigger problems to deal with in getting your RH under control.

I used to have serious problem with molds in Taiwan.... everything there molds because the RH never goes below 70% at any time.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

apply 93 percent rubbing alcohol.
or Denatured.
It'll dry fast.
then sand the set with a palm sander 80-120 grit.

Thin to the thickness you want.

Braces will take out the small warp.

Mike

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Mike Collins