Black stains on wood from Bessey parallel clamps (not pipe clamps)?

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Forum topic by eddit posted 04-10-2019 10:54 PM 1519 views 0 times favorited 9 replies Add to Favorites Watch
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13 posts in 669 days

04-10-2019 10:54 PM

Never had this before (least not that I’ve noticed) but I just took some walnut panels out of bessey clamps and had black stain marks where the glue line met the clamp. I had assumed this was only a problem for black pipe clamps. Have I just been lucky up till this point? Was it the walnut?

Ive cleaned my pipe clamps in the past with white vinegar, and then waxed them with Johnson’s wax to easily remove the glue. Other then that just regular parallel clamps.

9 replies so far

View bondogaposis's profile


5803 posts in 3155 days

#1 posted 04-10-2019 10:58 PM

Any time you combine wood tannin and iron and moisture (glue) you will get black marks, if you think it is bad with walnut, just wait until you try oak.

-- Bondo Gaposis

View SMP's profile


2248 posts in 709 days

#2 posted 04-10-2019 11:43 PM

Any time you combine wood tannin and iron and moisture (glue) you will get black marks, if you think it is bad with walnut, just wait until you try oak.

- bondogaposis

Yes i’ve found that woods that ebonize well get those black marks from the glue lines.

View gwilki's profile


355 posts in 2277 days

#3 posted 04-11-2019 12:23 PM

Bondo is right. Wait until you try oak. I put waxed paper between my clamps and the glue surface. It keeps the black off the wood and the glue off the clamps.

-- Grant Wilkinson, Ottawa ON

View Robert's profile


3788 posts in 2284 days

#4 posted 04-11-2019 01:13 PM

I put panels on top of spacers that hold off the bars about an inch.

Once clamped, you can clean the glue, too.

-- Everything is a prototype thats why its one of a kind!!

View eddit's profile


13 posts in 669 days

#5 posted 04-11-2019 01:14 PM

Thanks for the confirmations. I guess I’ve just gotten lucky in the past, never seen it this bad or deep. Luckily it’s on the “bottom” of the panels :)

View TechTeacher04's profile


447 posts in 2335 days

#6 posted 04-11-2019 02:26 PM

You could also apply a single layer of packing tape to the beam of the clamp, this will prevent the clamp bar from touching the work piece. If you are using pipe clamps you could cut a few slit rings from pvc pipe and use them as standoffs to prevent the contact.

View tbone's profile


312 posts in 4488 days

#7 posted 04-17-2019 09:05 PM

If your normal sanding won’t remove the black marks, try oxalic acid (Rockler…pretty cheap). It really works well on oak, and it should work on walnut.

-- Kinky Friedman: "The first thing I'll do if I'm elected is demand a recount."

View Mojo1's profile


286 posts in 3494 days

#8 posted 04-18-2019 12:40 PM

I keep a roll of wax paper in my garage and put that down between clamps and wood, keeps both happy.

View Gene Howe's profile

Gene Howe

12215 posts in 4232 days

#9 posted 04-18-2019 03:18 PM

Like Tech Teacher, I use clear packing tape on my pipes and Bessys. But, i like the pvc pipe idea very much.
I use Oxalic acid to bleach wood…evens out the color. I’m not sure about using it in selected areas.
Amazon sells it. 2lb for $13 with free shipping.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

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