The Woodworking Network started a new blog series on Finishing. Here's the portion of the article that's most useful for our readers of The Sandpaper Blog:
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
• 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
• 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.