Planing, sanding, and finish adhesion

[David Ragan]

Maybe this question belongs in Neanderthal or Finishing-but here it is:
I was just watching a Paul Sellars YouTube video, he said that in order for your finish to adhere, you should not really, for instance, plane with a blade honed on a 15K stone, etc-you'd have to rough it up a little first for your finish to adhere. I have read that abrasives used over 220 or so is a waste.
Water based finishes will swell wood fibers roughening them.
Mostly, i work with hardwood.
I have lots of really nice finishing stones and high grit abrasives. Am I just wasting my time and energy on all that?
Thanks, David

[glenn bradley]

For the type of finish he prefers this may be true. I generally go for the lightest film that will do the job. For a decorative box this may be a coat of shellac, for a kitchen table I may use a film of varnish as thick as typing paper. I do not use films heavy enough to hide the irregularities of 180 grit sandpaper but, going heavy and polishing the film is a valid finish choice. I have pieces that I sand to 600 and then use a buffing wheel on end grain. I have pieces that go straight from a cabinet scraper to the finish stage. Vive la différence.

[David Ragan]

If I did finish to 320 or 400, or whatever.....has anyone had a finish that didn't adhere? To me, this sounds impossible-for the finish to not adhere.

To take it further, I have finished a jewelry box with the abrasive cloths that are used to buff out aircraft windshields (MicroMesh for wood), and the surface felt so smooth I did not apply a finish. Has anyone ever used Micromesh and put a finish over that?

[glenn bradley]

I know poly can act up sometimes when being applied over itself without proper surface prep but, I have never had an initial finish cause trouble even when surfaces (like the end grain on these fingers) have been nearly polished prior to application.

GnG-BC-3rd-coat 005.jpg

I use primarily hand applied oil/varnish blends and have no experience with heavy coats of sprayed lacquers and the like so my experience is somewhat limited. I have sprayed poly early on and moved away from it but, did not have any adhesion issues. I do my work in southern California but, have pieces across the country. If any finishes have failed, folks have been too polite to tell me . . . just kidding, I think I would have heard about it .

[David Weaver]

I've never had a joint fail due to gluing on freshly planed surfaces. I'd defer to warren mickley in the HT forum who has done probably hundreds of times as many joints as I have, and he does not sand and he does not spare sharpness, either. That includes joints with liquid hide as well as PVA type glues or whatever titebond is.

As far as the sharpening, the proper use of the double iron on a common plane is more important in surface quality (and even-ness) than spectacular sharpness, but there is nothing wrong with spectacular sharpness and wanting a bright surface. Sanding a surface is a good thing to do if you want surface uniformity (which is a look that I think most people prefer, especially if they're staining inexpensive wood to make it look like something a little nicer). Planing (if you do it properly) will leave a little bit more depth and life in otherwise bland looking woods - despite magazine articles that suggest otherwise.

The amount of grain raising you'll get from various finishes will vary based on the wood and whether or not you've planed something cleanly. If you have, the grain raising will be much less on a planed surface than it is on a sanded surface.

Sharpness gets you ease in a cut, the thinner the shaving the more. And you'll probably never have a preference for less of it with a chisel unless you have overcuts in some paring cuts (So I personally don't think you're wasting time - it should take little less time to go to that level vs. a few notches below, anyway).

[Prashun Patel]

In my short experience, if you are building a film finish, then it's a waste of time and sometimes counterproductive to sand upwards of 220ish grit. The concerns about adhesion are largely limited to polyurethane. For most other varnishes and for shellac and lacquer, it does not seem to matter.

If you dye or stain the wood, sanding north of 220 can sometimes burnish the wood, preventing colorants from penetrating. This can actually be a good thing to prevent blotch, but can be a bad thing if you are trying to highlight grain.

If, however, you are simply going to put an oil or oil-varnish finish on it, then I always sand or plane my wood to a burnish (400g, etc). The oil doesn't seem to have a problem penetrating enough to highlight grain, and because there is no film, there is no concern about layer adhesion; on the contrary, having a burnished surface apriori really helps make the piece feel fantastic to your fingers.

[David Ragan]

As far as the sharpening, the proper use of the double iron on a common plane is more important in surface quality (and even-ness) than spectacular sharpness, but there is nothing wrong with spectacular sharpness and wanting a bright surface. .

You mean the cap iron, right? Setting is about a 1/64th from the edge, or even closer?

[David Weaver]

Cap iron yes. Closer than a 64th. A little inside of a hundredth in general for smoothing work, and somewhere around a hundredth for heavier work. I've never measured, but a good start is to get it as close as you can with a smoother and then start backing off until you don't have so much resistance and at the same time don't experience any tearout.

[Max Neu]

You can have issues if you sand with 220 or finer on some woods like hard maple. I use 2k poly and conversion varnish, and the data sheets for both products say not to sand bare wood finer than 180grit to avoid adhesion problems.