Why & How Do You Scuff Sand?
By Bernie Bottens | Posted: 04/19/2012 9:48AM
Now, very quickly, before you turn your attention elsewhere or roll your eyes in disbelief, let me try to engage you in this subject. I know this could be painful and, certainly, sanding is one of the least liked operations in the shop but…it must still be done. Here we go!
How do you scuff sand?
That’s a really good question and there are a lot of different answers to that depending upon the mindset of the person with the sandpaper in hand. I see how a lot of shops handle this task because I am in and out of shops all day long. I see what’s going on and I see that there are different approaches. So the more I thought about this question in the context of what I see from day-to-day, these images came to mind:
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• There’s the finisher who sands simply because he was told to do so — no other reason. Sandpaper simply has to be applied to the seal coat and then we move on.
• There’s the finisher who had a rough night last night and is unconsciously taking it out on a set of cabinet doors this morning.
• There’s the finisher who knows that he must scuff sand but doesn’t really know what it is he’s looking for, removing, or when or where to start and stop.
• There’s the finisher who uses the wrong tool for the task at hand.
• There’s the boss who doles out one finishing sponge in the morning and another after lunch. Sponges are expensive and not to be wasted.
• There’s the finisher who is so afraid to burn through the seal coat that he rubs his new sponges together to dull them before he uses them.
• Then too, let’s not forget the finisher in his muscle shirt who really gets into his work and sweats all over his project.
That being said, let’s ask the next question:
Why do you scuff sand?
• Modern coatings get hard and some get chemically resistant within hours. Subsequent coats will not rewet and blend with the layer below. The only type of bond that is possible between coats may be a mechanical bond created by sanding scratches.
• It’s true, in my experience, that most first coats make you look like a monkey’s uncle. They look horrible! But if properly scuffed, a good seal coat will make you look like a rock star after your second coat.
• The lacquer makes wood fibers stand up.
• Surface tension in the lacquer attracts it to those fibers and it builds up around them creating “pimples” in the lacquer that must be sanded away.
• Surface tension causes lacquer to pile up around the pores.
• Surface tension creates fat edges that need to be attended to.
• There’s always dust that appears as if by magic or “spooge” out of the gun that lands in the first coat
• There’s always a bug willing to commit suicide in your wet lacquer.
• Heaven forbid! You just created a run or sag.
All of these and more are the enemies of a glass smooth finish. And lest I forget, it is über-important to get rid of the sanding dust that you create. Again, it may not be rewetted by the next coat. Dust and debris are your enemy!
At the same time, the guy who sands his work and perspires onto the surface is the first one to call and say that he has fisheye issues. Wear at least a short sleeve shirt. The oils of your skin and certainly the deodorant that you wear will contribute to fisheyes. That’s doubly important with water-borne coatings. Remember, oil and water don’t mix.
Next week we are going to continue this discussion. Plan to return for that session where I will discuss the art form of scuff sanding. It is that, you know. I’ll be giving tips on how to make you look like a rock star in the spray booth by making you mindful of a few basic things.
Until next time…spray on!
About the Author
Bernie BottensBernie Bottens (WoodworkingNetwork.com/blogs)writes and teaches on the subject of wood and wood finishing in industrial woodworking. He and his wife, Carol, live in Vancouver, WA. Bernie has been teaching wood finishing to shop owners, shop foremen, spray technicians and finishers all over Oregon, southwest Washington, and northern California for the past 9 years. Prior to that, he owned his own cabinet shop. His shop credentials include apprenticing and becoming a journeyman exhibit builder. Before that he taught in the public schools for 20 years. Bernie is the owner of Kapellmeister Enterprises, Inc. and Kap Coatings Consulting. Reach him at email@example.com.