Tracking Contamination Back to the Source

      A finisher thinks tack-rag residue may be contaminating his finish. But colleagues suggest many other possible sources of the trouble. July 24, 2005

Question
I am looking for some advice about tack rags. It seems to me that the sticky wax on them would be there when you start to lay down a finish. I've been having a problem with spots in my finish (deft semi-gloss) due to little indentions about a small finger print size, but I know the wood was flat and sanded very fine. Does any one have any suggestions?

Forum Responses
(Finishing Forum)
From contributor C:
Tack cloths don’t have a sticky wax, they are impregnated with Linseed oil, which is also a component in some stains that a topcoat has no problem going over. However, being sticky, they are prone to grabbing nasty residues off of your hands and then transferring them to the wood when you wipe them down.

I use tack rags in my finishing room and have never had them cause a problem in the finish. I'm also in the habit of cleaning my hands every time I come back into the finishing room from a break, lunch, or contact with laminate work. So far, every single instance of finish contamination can be traced back to the use of LamiLube out in the shop.



From contributor C:
Go watch the person who did the sanding. If you don't see anything suspect there, like eating candy while working, or a pneumatic sander burping oil, then go to where the piece was cut or milled and observe their process. Follow the piece backwards through the shop and you will find your culprit.

As the finisher you will know if you, your tools, or your coatings have been contaminated. The guys out in the shop are generally clueless as to what can screw up a finish though. The last time I had fisheye pop up in my shop, I traced it back to the edge bander. Sure enough there was that can of LamiLube, and they had squeezed the finish work in between runs of banding PVC to laminate without cleaning the wheels off. The pattern of contamination on the pieces will help clue you in on where in the process it happened.



From contributor R:
Pressing down with too much pressure can cause the pattern of the Tack rag to telegraph itself onto the surface and will cause you a finishing problem for you.


From contributor B:
Make sure you are not using serrated sandpaper. I have had problems like yours and make sure I stick with non-serrated paper and the problem gone.


From contributor J:
The most important thing in using a tack rag is to fluff it before using. Unfold it as much as possible when new, and gently wrap it up to be fluffy, not flat and firm like new. Then you can lightly wipe the surface without much pressure.

I stopped using them long ago. I now use a clean rag with just a mist of Endust quickly sprayed over it. Some may disagree that Endust is ok, but it doesn't have silicones and does a better job. It seems to take the static out and really pull the dust out of the pores. I like it better than tack rags. I spray lacquer and have never had a problem with it. I think the trick with it is to not to get the rag wet with it, just slightly misted. Then after using I just throw the rags in the washer and reuse them. Try it, and you'll be amazed at the dust it pulls up.



From contributor G:
I stopped using commercial tack rags early on - not that I had that much of a problem with them - I just didn't trust them. I sometimes bottle-spray naphtha on cheese cloth and gently wipe; other times I bottle-spray 1/2# cut of clear shellac on fluffed up c/c and wipe gently. I haven’t had any problems so far.


From contributor W:
I spray a little finish on a rag, let it get sticky, and wipe the surface with that. It’s like a dust magnet. You do have to use a light touch to keep it from sticking to the surface.


From contributor D:
I sanded the table down with 220 and then a fine sanding sponge, cleaned and lightly tack ragged it and put down another coat and the very same spots showed up. It's like the finish is being sucked through a straw from underneath. Everything I use is new, so there is no chance it could be contaminated.


From contributor A:
From a distance, it sounds like it's not a tack rag issue, but more of an issue of the wood taking differently in certain spots. That's why we have one standard rule in our shop. No matter what we are doing, we always spray a one pound cut of de-waxed Shellac down before applying any type of finish. We even do this on paint grade work before putting down the primer. Shellac is very quick and gives you so much safety factor against any underlying contaminants that we feel it's worth it.



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