|Forum topic by JeffP||posted 05-29-2015 06:45 PM||903 views||0 times favorited||17 replies|
05-29-2015 06:45 PM
Ok, so sometimes I come up with a question while I’m working…but other times I just see something here on LJ that surprises the heck out of me and want to know more.
This is one of the later category. It is also admittedly “splitting hairs” and rather low in relevance. Kind of a snarky post upon re-reading. Please look past that. I hope to learn something from the responses.
On another thread, somebody mentioned using “600 grit” sandpaper between coats of waterbased poly.
Ok, fine. Normally I think of “220 grit” when I think “so fine it is hardly worth the trouble”. So 600 kind of bowled me over.
I googled and discovered that some Germans are actually making money selling 7000 grit sandpaper!
I would think just plain old copier paper would have a “grit” rating of maybe 1000. What’s the deal?
I looked up grit size on wikipedia and found it is “almost, but not rigorously linear”. That is to say it is certainly not a logarithmic progression or anything of the sort. It is also not directly related to the size of the particles by any obvious formula. (example: 100 grit has particles of size 140 micrometers, and 1000 is NOT 14, but rather 10.3)
Anyway, 600 grit for between coats? Seriously? Why not just rub your calloused hand over it? Or rub it on your t-shirt?
What is the stated goal of that between coats sanding, and is it really better served with such a high grit? Would more gentle use of 220 grit accomplish the same thing? Can one of you provide me with an “explain it to me like I’m six” sort of explanation. “You are trying to remove all of the———- without disturbing the—————.”
The stated size of the grit particles for 220 is 68 micrometers. Both that and 600 grit (25 micrometers) fall within the alleged range of the thicknesses of human hair (17 for a georgia peach face hair to 181 for an RCH).
Does it make a difference? I have gently used some steel wool for between the coats “sanding”, and it seemed like it went fine. Not sure I would have known the difference if I had skipped that step. I am wondering if my senses are just not finely tuned enough to know the difference.
-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.