Sandpaper grits

[Mike Mortenson]

I was just curious what grits everyone uses to sand wood. Can you actually sand too much and with too fine of paper?

[Dave Anderson NH]

You can indeed sand too finely for many woods and end up burnishing the surface. The level to which you sand also effects the amount of stain (not dye) which will adhere to the wood surface and how even it appears.

Personally, if I do sand a surface (I usually hand plane it) before finishing, I never go higher than 220 grit except on turnings. Most of the time any sanding above 150-180 grit doesn't improve the surface very much. What is more important is finishing the finish. By finishing the finish, I am refering to rubbing out the finished surface after letting it cure. This levels things out, removes any dust nibs or brush marks, and leaves a smoothe and silky to the touch feel.

My normal sanding schedule is 100, 120, 150, and 220 if necessary.

[Chris Padilla]

Mike,

One thing I like to do is to practise your sanding and finsihing on scrap. You may find 150 grit is plenty. Then again, for fun, sand through to 400 or 600 and see how the finish looks. You might like it better! As Dave alluded to, you have various choices dependent upon what you like at the end.

[Dennis Peacock]

General sanding and just before staining I sanding through 180 grit, wipe and stain. If it's a clear finish, I usually sand to 220 grit. If you want a really fine finish, then you need to start sanding with 320 AFTER 2 coats of clear finish has been applied and then only "lightly". Apply another coat, dry and sand with 400 grit. If your using gloss you can always dull the clear finish by using some 0000 steel wool. If you use a flat or semi-gloss finish, you can't get it any shinnier by polishing or rubbing it out due to the flattening agents in the finish. Everthing I put a finish on is with gloss to allow me to control how much sheen I want or is desired.

[Howard Acheson]

Sanding wood--hard or soft--beyond 220 does little more than burnish the wood making staining difficult. This is particularly true if you are using a pigment stain which sits on the surface and relies on "nooks and crannies" to impart color. Softer more porous woods can be sanded to to 220 but harder less absorbent woods may stain best if only sanded to 150.

A number of years ago a shop I was involved with did series of adhesion tests with various finishes and sealers. As part of this test we explored adhesion based on sanding grit. We found about the same adhesion up to 180 - 220. Beyond 220 adhesion dropped off due to burnishing of the underlying wood particularly when non-linear machine sanders were used. This was tested on birch panels. We also found that the resulting smoothness of the first coat of finish was not materially affected by the smoothnes of the underlying wood for sandpaper grits between 150 - 220.. Thin finishes such as lacquer could be affected by grits less than 180. The smoothest surface substrate for final finishes was obtained by sanding lightly after the first coat of finish was applied and dry. Which makes the case for a thinned first coat of finish.

So our conclusion was that sanding beyond 180-220 was a waste of time and could be actually detrimental. But, there was a big appearance affect if the surface was not hand sanded in the direction of the grain using the highest grit used on the sanding machine. A flat pad sander produced a much flatter surface than a ROS. However, both required final hand sanding with the grain for optimum appearence. If not hand sanded, swirl scratches would show. Final hand sanding using a sanding pad in the direction of the grain is a must.

To carry it one step further, sanding at 320-400 grit after the first coat and subsequent coats was the optimum. Any finer and adhesion problems were encountered. Any less and the sanding marks were very likely to show through. No improved appearence was noticed by between coat sanding beyond 400 for varnish. 400 was the sweet spot for thinner finishes. Between coat sanding was always done by hand whether for flattening or for adhesion.

I think you will find similar thoughts in the popular finishing books but YMMV.

[Jim Becker]

There is a nice little article in the new October 2004 issue of WOOD Magazine that speaks about sandpaper grits and has a table crossing the two "rating" systems. It may be useful if you buy paper from multiple sources, especially if one or more supplies product with the European markings.

[Frank Pellow]

Mike, thanks for asking this question. And, thanks to all those who responded with valuable information. I certainly have learned some things that I suspected but did not know.

[Dennis Peacock]

If the sandpaper grit is stamped on the back and it has a "P" stamped on it? That is grit paper made to European standards. The grits are different from U.S. grit standards and European grit standards. The wood magazine article is pretty good. :)