Removing bar clamp discoloration from cherry plywood

[Robert Rifkin]

Hi,

I'm building a cabinet out of cherry hardwood and veneer plywood. The cabinet is mostly completed, but yesterday i noticed a stain on the veneered cherry plywood that was not there when i bought the plywood, but was probably introduced by my cast iron bar clamps. there was no glue in the vicinity of the stain, so I suspect that somehow the simple contact between the clamps and the cherry caused the discoloration. I have not finished the cabinet yet (i'll probably use watco danish oil) but I was wondering if anyone has any suggestions for removing this stain. it is a couple of inches long and around 1/2" wide. the wood is blackened in the area.

I tried light sanding with 200 grit sandpaper, to no avail.

thanks in advance.
bob

[Chris Fournier]

Hi,

I'm building a cabinet out of cherry hardwood and veneer plywood. The cabinet is mostly completed, but yesterday i noticed a stain on the veneered cherry plywood that was not there when i bought the plywood, but was probably introduced by my cast iron bar clamps. there was no glue in the vicinity of the stain, so I suspect that somehow the simple contact between the clamps and the cherry caused the discoloration. I have not finished the cabinet yet (i'll probably use watco danish oil) but I was wondering if anyone has any suggestions for removing this stain. it is a couple of inches long and around 1/2" wide. the wood is blackened in the area.

I tried light sanding with 200 grit sandpaper, to no avail.

thanks in advance.
bob

Try diluted vinegar on a test sample. It may be all you need to remove the stain and not alter the cherry colour.

[Dell Littlefield]

I have had very good luck with oxalic acid (wood bleach) on rust stains on teak, oak and other woods. I don't think I have tried it on cherry but that would be my first choice. It comes in a powdered form and you mix a paste and put it on the stain. Really worked well for me.

[Myk Rian]

^^^^^^^^^^^
Arm and Hammer washing SODA has Oxalic acid in it.
Used to remove rust in an electrolysis tank.

[Steven Hsieh]

Is there oil on the clamp?

On the wood, Wipe it down with mineral spirit

[scott vroom]

It doesn't help with your current problem, but one method to avoid those pipe stains is to place a sheet of wax paper between the clamp and the wood. This is particularly useful where the pipes are crossing over an area where there is glue squeeze out, or on any project where you're working with an extremely thin hardwood veener where heavy sanding isn't an option.

I recently purchased galv pipes to make up some new pony clamps...thought I'd give it a try (to avoid the staining problem). Some folks think pony clamps slip more easily on galv pipe, I think because it has a slightly larger OD than black pipe. So far I haven't noticed any slipping.

[Jim Andrew]

I was having this problem a few years ago, and knew oxalic acid would take care of it, but could not find a supplier.

[Kent A Bathurst]

It doesn't help with your current problem, but one method to avoid those pipe stains is to place a sheet of wax paper between the clamp and the wood. This is particularly useful where the pipes are crossing over an area where there is glue squeeze out, or on any project where you're working with an extremely thin hardwood veener where heavy sanding isn't an option.

I recently purchased galv pipes to make up some new pony clamps...thought I'd give it a try (to avoid the staining problem). Some folks think pony clamps slip more easily on galv pipe, I think because it has a slightly larger OD than black pipe. So far I haven't noticed any slipping.


FWIW.........

On my black-pipe pony clamps: 1" PVC pipe. Cut to 1" +/- lengths. On the bandsaw, remove 40 pct of the circle. The remaining piece snaps onto the 3/4" pipe, but is easy to slide or remove. 2 pieces act as stand-offs. The pipe doesn't touch the wood or the glue squeeze-out. Every one of my kajillion pipes have 2 installed. Never had a bit of trouble since I went this route 10+ years ago.

I also have them screwed into cripples on my "clamp wall". The pipe clamps snap securely in place for storage.

[Kevin Bourque]

Is it possible that its a "suntan" mark?

[Peter Quinn]

I was having this problem a few years ago, and knew oxalic acid would take care of it, but could not find a supplier.

Oxalic acid is your best first choice. It removes stains caused by tannins in the wood reacting with iron. You don't need to have glue in the picture, it can happen just from contact by taking on moisture from the air in the room. I've taken back some unfortunate accidents that got deeply iron stained (long and different story) by a coworker from what looked ruined to the point you couldn't tell it ever happened. I buy it from my local corner hardware store, I think the borg and Amazon have it among others. Chances are the veneer is so thin you cant sand it out.

[Howard Acheson]

Oxalic acid is the bleach used to remove mineral and water stains from wood. YOu can get it at most paint stores.

[Jim Andrew]

I was in a cabinet shop and we bought our finishing supplies from the local Sherwin Williams store, and they said it wasn't available. I also called the other local paint stores, and nobody had it. At that time.

[Kyle Iwamoto]

I'm fairly certain Barkeepers Friend uses oxalic acid as an active ingredient. You could give that a try. That's available just about anywhere.

[Edward Dyas]

Expanding on what Kevin Bourque said, cherry is bad to turn dark from exposure to sunlight. I saw a guy onetime lay a sawblade on a fresh sheet of cherry plywood sitting in the sun. After lunch he came back and picked up the sawblade and the rest of the sheet had darkened except for the image of the saw blade in the sheet. I'm wondering if while you had your clamp on the cabinet the sun darkened the rest of the sheet.