Why sand between finish coats?

[MilDoc]

I always have, mainly because the cans of finish say to. But I am reading Michael Dresdner's book, and he flatly states:

"If it has been less than 2 weeks since the last coat was applied, there's no need to sand between coats... should lightly sand with 320-grit (if longer than 2 weeks) ... "

But sand between coats only if needed to remove imperfections in the finish.

He doesn't state whether he's talking about oil or water-based finishes, seems to imply any finish.

How 'bout that?

[lcm1947]

Boy that doesn't seem right but how would I know. Maybe he means something else though and we are just not understanding what he means. I got " Understanding Wood Finishing by Bob Flexner for Christmas but haven't gotten to the sanding section yet. Anxious to see the replies too.

[MilDoc]

should have mentioned that the quote comes from Dresdner's book Wood Finishing Fixes, which is question and answer format, and the quote was the answer to the direct question "Do I need to sand between coats when I'm finishing?"

[gerti]

Hmm... I'd buy that for finishes where the solvent will also dissolve previous applications, like shellac. But I doubt that would hold true for example for PU.

[cabinetman]

Some habits are formed due to experience, and some are just habits. My take on the statement about the two weeks is that most finishes will have completely cured in that time. Granted, some solvent finishes like lacquer will soften the undercoat, but it wont level it to any degree. If the surface is rough or orange peeled, that finish will read through to the next in some form.

Other finishes will have cured also, that aren't subject to characteristic change like polyurethane, either water base or oil. I'm a believer in the theory that the finish depends on what's under it. I sand in between coats, just because. All subsequent coats get better and better. I'm also a proponent of putting on just enough finish. Overbuilding can lead to imperfections due to expansion and contraction. Unless a finish is catalyzed, subsequent coats inhibit the ability to air dry to a cured state.



A THING OF BEAUTY IS A JOY FOREVER - John Keats

[Ken Massingale]

With no background on his statement it's hard for me to comment. Feeling the finish after the first couple of coats of poly will definitelyshow some roughness, 'if' the stock wasn't sealed. To me that should be sanded smooth before the following coat.
However, I have found that when a couple of coats of Sealcoat are applied, followed by oil finish, then the finish is quite smooth after the first coat. True, that's 3 coats, but the Sealcoat can be sanded after 45 minutes. (depending on shop conditions)
k