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Hi everyone,
I'm looking for some input on a problem I'm facing with my bending process. I've scoured through the forum looking for a reason to my problem, how to prevent it from happening again and how to fix it.

I'm using a Fox Bender to bend my sides with the following sandwich : slat/blanket/slat/kraft paper/wood/kraft paper/slat. The slats I've made from galvanized duct work and seem to work great. I'm also using reverse osmosis water. I wet the paper and then squeegee the paper off on the side of my bench. I lightly mist the wood as well and then squeegee the wood off as well.

But I keep getting staining on the inside of the sides, and the outsides look great! I've bent two different woods now, wenge and bubinga and got staining on both. It was workable with the wenge because the wood was already dark. I bent the bubinga last night and this is the result :


I start my bends once I see steam and the sides bend like butter. This is usually around 220. I'm not waiting for the blanket to come up to the large temperature numbers I see everyone else using but the bending seems to go fine. With the wenge, I only heated once, then allowed to cool and I got staining. With the bubinga, I heated the side, allowed it to cool and then reheated the side with the same staining. Is it an issue of the inside of the bend not coming up to temperature like the outside where the blanket is?

And now the next question - apart from sanding, is there a way of removing this staining? I'm glad the outside looks perfect, but I want to clean up the inside of the rims as well.

Thank in advance guys, I really appreciate any input on fixing this problem.
Rob

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Rob Flindall
Flindall Guitars
http://www.flindallguitars.com
https://www.facebook.com/FlindallGuitars

Thanks Todd - I'll definitely try the foil. I have a zebrawood set and sapele set still to bend. Keeping my fingers crossed.

Now in your experience, will this sand out, or does this sort of staining go pretty deep into the wood?

Rob

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Rob Flindall
Flindall Guitars
http://www.flindallguitars.com
https://www.facebook.com/FlindallGuitars

Are you using distilled water? Any mineral in the water will cause staining!

I went to Culligans to pick up some distilled water but they no longer sell it as they now have reverse osmosis treated water. The lady there said it's 99.99% pure water. So there shouldn't be any minerals in the water.

I'll definitely try the oxalic acid - I just need to find a source for it here in Canada. Home Depot didn't sell it, but I understand that some pharmacy's may carry it.

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Rob Flindall
Flindall Guitars
http://www.flindallguitars.com
https://www.facebook.com/FlindallGuitars

Home Depot didn't have the oxalic acid?

Do you have a "paint store" nearby? Sherwin williams, Benjamin Moore, Porter, etc.?
A very common use for oxalic acid is cleaning of decks and driveways before sealing.

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Always have plenty of sandpaper; it's rough out there!

Well at 5 minutes to closing time, the ladies in the paint department didn't seem too interested in figuring out if they carried the product. I did some research tonight and saw that deck cleaning was a common application. Thompson's deck cleaner wouldn't happen to be oxalic acid now would it? I'm going to go back to HD and have a good look around the deck cleaning dept and driveway sealing dept - thanks for the tip! We have a Sherwin Williams in town too, so I'll check there if the HD falls through. I'm really keeping my fingers crossed that the oxalic acid will clean up those stains.

Question though - once I find some oxalic acid, how do you apply it to the wood? Wipe on, wipe off? or do you let it sit for a bit?

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Rob Flindall
Flindall Guitars
http://www.flindallguitars.com
https://www.facebook.com/FlindallGuitars

This is just a crazy thought, but try oxyclean and then a little saw dust to pull up the oxyclean ! Sawdust really pulls stains out of concrete!

Oxalic acid can be poisonous so it might be difficult to buy under that name. I have found that farm vet supplies carry various chemicals under their correct names.

Washing products that remove blood stains will probably comtain oxalic acid.

Reverse osmosis water is as good as distilled but dehumidifier water is probably as good for most shop uses.

Bob

I had a staining problem with bubinga and it sanded out just fine.

Thanks guys! Oxalic acid, apparently, is very difficult to find here in Canada. The only place I haven't gone yet is a local pharmacy to have the product ordered in. I did find a Behr deck wash, but I think the concentration is too low at 10% oxalic acid. I'll let everyone know how I make out. Thanks for the application info Todd.

Unkabob - I've been running a dehumidifier in my shop all summer and throwing the water out! I'll start bottling it now and calling it Luthier Magic Water. Lol.

Rob

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Rob Flindall
Flindall Guitars
http://www.flindallguitars.com
https://www.facebook.com/FlindallGuitars

I've been wrapping my sides in paper, helps hold some moisture during bending and prevents staining at the same time.

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Jim Watts
http://jameswattsguitars.com

I wouldn't recommend neutralising with baking soda. Will turn some woods black (Aus. blackwood/black acacia particularly comes to mind). Best to keep the pH slightly acidic, so wash off with just water or dil. acetic acid (vinegar) if your water supply is alkaline e.g. limestone area.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Just sand a bit; it's likely just on the surface

WOWZA! I purchased a product from Home Depot called Behr Premium All-in-One Wood Cleaner that contains a less than 10% concentration of oxalic acid. I tried the product on my bubinga sides and voila! Here are the before and after pictures :


I am duly impressed with the results! Not bad huh?

Rob

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Rob Flindall
Flindall Guitars
http://www.flindallguitars.com
https://www.facebook.com/FlindallGuitars

Nice!!!!
Another source is a granular cleaning product called "Bartenders Friend" whose main ingredient is oxalic acid.

Hey Thanks for this thread. I took a Australian blackwood side out of my fox bender yesterday morning and had a large black stain on the inside at the waist. I did have it wrapped in kraft paper but still got the stain. I tried the Behr all in one wood cleaner with an old toothbrush and then used a mixture of warm water and white vinegar to clean it off. It worked great. Thanks again - Mike

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guitarsbygiltzow.com

Nice! I'm glad it worked for you too Mike. I used very little of the Behr product - so a little goes a long way. Given the size of the jug, we probably have enough for, say, 500 guitars? Lol. Good luck on your build!

Rob

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Rob Flindall
Flindall Guitars
http://www.flindallguitars.com
https://www.facebook.com/FlindallGuitars