Oil Marks From Clamps

Article - August 9, 2010

Mike wants to know how to prevent those annoying oily marks left on a project from the rubber feet on clamps.

Thanks for all the advice you’ve provided in years past. It’s been a while since I asked a question but there is one that has been on my mind for some time. Clamps are a must have for any woodworker. It never fails though that when I am working on a nice furniture piece and I have to use a lot of clamps say to laminate a leg out of multiple boards or something of the like, when I go to remove all the clamps they leave the familiar little oily dots or marks where the rubber feet on the clamps meet the wood. Sanding never seems to do the trick, and inevitably I end up having to run the piece through the planer or jointer to take a minute layer off to remove the marks. Have you ever had this problem and if so how did you remedy it? (Picture to the left shows a simulated/exaggerated oil spot)

I have indeed had this problem many times in the past. I have even observed this when using rubber router pads during sanding operations. The rubber seems to transfer a small amount of oil into the wood fibers, especially when compressed in a clamping situation. Given the clamping pressure and length of the exposure, its no wonder we can’t get these marks out with simple sanding alone. So my remedy is much like yours. I remove the offending materials either by planing or scraping. And if the mark isn’t too bad, I can sometimes get away with sanding alone. I haven’t tried it yet, but you may want to try wiping the surface down with a little mineral spirits to see if that helps clean things up a bit.

Of course, the best thing to do is prevent the problem from happening in the first place, and that’s where cauls come in. A caul is nothing more than a small piece of scrap wood that goes between the clamp and the workpiece. Not only will this help avoid the oil issue, it will also prevent any denting that may occur from excessive clamping pressure. You can also get a lot more bang for your buck by using wider cauls to help distribute clamping pressure. So there are a lot of good reasons to use them. I actually keep a small collection of cauls near my workbench just for this purpose.

Now if you want to get real fancy, you can glue strips of cork onto your cauls. This will put a firm but flexible layer between the caul and the workpiece, protecting your masterpiece even further. But whatever you do, don’t line the inside of the caul with rubber!

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