Is 120 grit enough?

[Hans Braul]

I vaguely remember reading in a Woodworking magazine that tests had shown that sanding beyond 120 grit prior to applying shellac or varnish was not only unnecessary, but in some cases counter-productive because higher grits tend to burnish the surface and cause blotchiness. Can you fine folks confirm or refute this?

I'm just starting to sand the parts of 7 cherry dining room chairs and I sure don't relish the thought of sanding any more than I have to!

Many thanks
Hans

[Kent A Bathurst]

I'd have a real hard time believing that is true at 120g. If you had said 180, I'd agree. Burnishing doesn't start till higher - like 320 IIRC. If you are using shellac, the cherry won't blotch. If you aren't using shellac, then use some anyway - one or two wash/seal coats @ 1.5#, and the cherry won't blotch

[Faust M. Ruggiero]

For years we sanded to a silky smooth surface. We sanded cherry until not a scratch was left. We stained and sprayed nitrocellulose with great results. The manufacturers of spray finishes began to develop finishes that were harder and less likely to be damaged for kitchen applications. Catalyzed lacquers and conversion varnishes were developed not only to last longer but to save labor in cabinet shops. Where we would spray 5 or 6 coats of nitrocellulose, two coats of CV now do the job. They basically encase the wood in plastic. They need a coarser surface to assure adhesion and since they are so thick, they level out and fill the 120 sanded surfaces. This process saves a lot of time.
When finishing furniture I still spray a non catalyzed lacquer and use several coats. I sand cherry until it almost shines. The better the sanded surface, the better the ultimate finish. If you can afford the time, hand sanding to 220 or even 320 will allow you a much clearer grain pattern showing through the finish. As for blotching, the finer you sand the open grain portions, the less stain they will absorb, the less they will blotch. I sometimes burnish cherry with 0000 steel wool before staining.
fmr

[Thomas Pender]

As are really sharp smoothing planes. Plus you get the very desirable handfinished look. Point is that for flat surfaces the finishes were always beyond 120, 150, or 180 grit sandpaper without using sandpaper. I really do not know just how smooth they were or are now, but when I use a cabinet scraper correctly, which is not always , it looks almost burnished like Faust is talking about and it feels as good to me as 320 grit Norton.

Try sanding with 220 some time, vacuum and then scrape clean - you will love the result. The wood just shines.

[glenn bradley]

150 is too rough for me. Depending on the material I will stop at 180, 200 and sometimes up to 400-600 for end grain burnishing or other effects. The film build required to bury 150 sized scratches is more material than I want to lay down during finishing. I mostly pad however, I don't usually spray.

[Tony Bilello]

I also agree that 120 is way too low to stop at. I generally stop at 180. I will go to 220 on very rare occasions. The truth of the matter is that the rougher the surface the more likely it is to suck up stain and the more coats of clear finish you will need. There is a reason that most woodworkers, cabinet shops and manufacturers stay between 180 and 220 grit. It is the most economical in terms of both time and materials.
I think this goes back to "don't believe everything you read."
Most magazines/periodicals do not check for technical correctness. If you are the writer, and that is the way you do it, then that is the way you do it and the editors are not going to change anything. The easiest way to get published is have an article 'ready-to-go', photos and all. The editor has tons of stuff coming across his desk. Which ones will he select? The easiest ones !

[Hans Braul]

I now recall the article I mentioned (had to rummage around in that dusty noggin for some time!). It was FWW #189, Jan/Feb 2007. It reported results of a test as follows:
3 types of wood: Cherry, White Oak, Tiger Maple
3 types of finish: Watco Danish Oil, Zinsser Seal Coat Shellac, Zar polyurethane varnish
For each combination he sanded up through various grits to as high as 600. His conclusions:
for non-blotchy woods and film finish, 150 grit is as high as you need to go. For blotch-prone boards, 400 is recommended. For oil finish, 220 grit. In my case with cherry, BLO then shellac, then sprayed lacquer, I will go up to 220 (I actually don't have any sheet sandpaper between 120 and 220, so I figure this should be safe.

I really appreciate all the input. If you have access to the article I refer to, I'd be interested in your take.

Regards
Hans

[Andrew Gibson]

I think I read something similar in FWW, but think it was 150 they said not 120. I would have to dig out the issue to double check, but i think they were talking about popping figure.

I usually sand to 220on cabinet work. Currently I am working on a rocker that I shaped with a microplane and belt sander with 80 grit belt. Then moved to hand sanding with 120, then 150. There is simply to much surface area to justify trying to go above 150 and with it being ash the grain will hide all the other imperfections, hopefully. Now my plan is to sand after the second coat with 180 then 220 after the 4th. hopefully it will turn out well.

[Hans Braul]

Andres, you're right - the article suggests 150 is usually adequate, depending on the type of finish being applied. The thinner the finish and the blotchier the wood, the finer the grit.

Hans