I would appreciate references on the use of hand planes and finish adhesion.

I build custom furniture and teach furniture finishing. At a recent workshop a nationally known woodworker stated that a hand-planed surface provide good surface adhesion without resorting to sandpaper. The research and the opinion of most professional finisher does not support his position but when I re-review the literature I could not find any studies that tested adhesion using hand planes; mechanized planers yes but no hand planes.

You're probably not going to find many tests on this because it's going to vary a lot--- so many variables here.

People vary significantly in their ability to keep a plane sharp, used at the proper angles/methods, etc. Those all are going to effect the adhesion of finishes, and that's going to vary from one finish to the other.

And obviously that will also vary from one wood to another, and one grain pattern to the other.

Personally I would not have any problem at all making a gentle pass with some 180 grit just to give a tiny scuff to the raw wood surface for finishing.

If this is an oil finish, there shouldn't be any trouble at all.

A properly sharpened hand plane leaves a surface with very clean, open pores. Sandpaper will give tooth to the hard grain, but also leave slightly closed pores since it was not as cleanly cut with the abrasive. I vote for good adhesion after a hand plane. I doubt if all the finish fell off hand planed furniture before sandpaper was commonly available.

Gordon, where do you teach at?

Depends on the finish. Penetrating oil finishes require no abrasion. They soak into the wood.

You will be hard pressed to find any company that makes film finishes which would say its ok. Most finishes require 240 grit at the very least for mechanical bonding to a substrate(typically 120-240). Even between coats the manufacturers recommend 240-320 grit. Some of the waterborne finishes can get away with 400-800 grit between coats.

In other words the vast majority of experienced finishers would say no.

I think there are a lot of factors here - the wetting characteristics of the finish, etc.

I was gonna pull out my little 300x microscope, and see what i would see, but it turns someone did one better:

If you look, you'll see they put drops of water on it, and also examine it under a powerful microscope.

While it's true that a handplaned surface leaves very clean, open pores (and this is obvious) , you can also see what happens when they put a drop on it: The smoothness and cleanliness of the surface causes it to become hydrophobic.

This is not entirely surprising given the relative size of the pores in most wood vs finish molecules/etc.

I think the conclusion is pretty obvious:

1. Closed grain wood - handplaned is a really bad idea.

2. Open grained wood - Still seems like a bad idea given what the video shows, but maybe an okay idea with big enough pores.

I think the TL;DR is also: This is not going to provide surface adhesion, the person is pretty wrong (and doing a little science would have shown them this).

Fantastic video, DannyB
Thanks a lot, very good to teach our people here.
Hugs for everyone

DannyB, thank you! What a perfect teaching video.

Gordon