I just completed the finishing work on some new red oak stair treads, railings and newel posts. The installer sanded the treads to 80 grit with a wide belt sander. The railings and newel posts were done to about 150 grit out of the box. I found that the treads, at 80 grit, took the 2 coats of stain exactly as shown on the Minwax color chart. However, the railings and newel posts needed 4 coats of stain to get close to the tread color.
Any general suggestions as to where to stop sanding hardwood projects?…….Softwood projects?
Replies
Well for stained archaetechual projects like stairs and cabinetry I stop at 220. So do most of the shops I know. 220 sanding marks will not show in the stain/finish. If it is something special like furniture I might sand to 320, but really it is how the finish itself is finished out that matters.
Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
I stop at 220 on the wood and 1500 after the last coat of finish
Rich
I usually stop sanding when all the woods gone and it's lying in a pile of sawdust on the floor,for me that's a good rule of thumb that i've sanded juuuuuuust a bit to far.... Not Really I'm just funning you all a bit. As a rule I don't like to sand much past 220 grit mainly so the finish has more of a tooth to hold onto. Of course this also depends a lot on the finish that I'm using at the time and the species of wood that the projects built from.
Sincerely,
Jim at Clark Customs
Like Jim, I don't like to sand past 220 if there is any staining with pigment involved because as he says there's not much for the stain to hold on to. In fact I never sand beyond 220 in those situations regardless of the wood species. I typically don't like to work with anything courser than 120 or 150 either. If there is no stain work of any kind then I prefer to sand to 320.
Here is some info that may help.
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. If you are planning an oil or oil/varnish finish, sanding to 220-320 works fine.
A number of years ago a large cabinet/custom furniture 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 and appearence of the first coat of finish was not materially affected by the smoothnes of the underlying wood for sandpaper grits between 150 - 220.. 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 not necessary and could be actually detrimental.
But, most important was that 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 could 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. 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.
Finally, the first coat of ANY finish will raise little shards of wood and cause them to raise. When the finish dries these hardened shards are what causes the surface to feel rough. Sanding with 320 paper will remove these hardened shards and subsequent coats will go on smoother. We never pre-raised the grain when using water based dyes or waterborne finishes. We just smoothed the surface of the first or sealer coat.
I think you've mentioned the adhesion tests before. I remember someone two or three years ago saying the same thing and I had thought it was someone else but it must have been you. I'd never really thought of adhesion between the wood and the finish before that, but it makes complete sense. I've practiced virtually everything you stated for a number of years now. It was really based just on my own experience. It's nice to see it backed up by more methodical testing, which is always a good idea.
With catalyzed finishes it seems counter-intuitive but in fact sanding with too course a grit can actually interfere with optimal adhesion because of how the finish chemically cross-links as it cures. Too course a grit can also cause the finish to swell up in deep scratches and produce a bump sticking up above the surface for the same reason. This is a well documented and established fact with catalyzed automotive paints and clears. Sand-scratch swelling is arguably less important in many respects on wood because you're not usually going for a perfectly level, very high gloss surface, plus the optical factors in play are fundamentally different because you're not trying to showcase only the color directly underneath the clear topcoat, the wood grain underneath the color is typically the real focal point which is radically different from automotive painting optics. But it's still something worth keeping in mind.
The one question I have is how you deal with pigmented stains with the thinned sealer coat? I always have problems with sanding through into the color, even using 400 grit. Other than that one issue, my experience is consistently not only that it produces a better finish but that flattening the surface is vastly easier over a single thin sealer coat than at later stages (i.e., not sanding that initial coat) or after having put on a heavy sealer coat. Even so, with pigmented stains I typically opt either for a heavy sealer or two thin sealer coats before I begin sanding operations. Where this really becomes a royal PITA is with wiping stains where the wiping rags have left tiny bits of fiber snagged on the wood surface, which is no fun to flatten out.
Other than that one issue I fully concur with everything you said.
Edited 6/3/2007 2:43 pm by Kevin
>> Even so, with pigmented stains I typically opt either for a heavy sealer or two thin sealer coats before I begin sanding operations.Yup that's really the only choice. With oil based varnishes, you can overcoat without sanding as long as you do it within 8-10 hours. Once you get on the second coat, wait 48 hours and then sand with the 320. For the past ten years I have mostly used a thinned wipe on process. I apply the first two coats within about an hour or two, let it dry for 48 hours and then flat sand. Rarely have I sanded through to the stain.Howie.........
Stop sanding when there's no more wood left.
:]
Expert since 10 am.
Short answer: you stop sanding when you cannot see with the naked eye any sanding scratches.....and when it feels "right" to the touch.
But this varies with the type of wood and according to what may have been applied (sealer, first coat etc). Example: red oak-you can get away with 180grit (must be with the grain), but if you are to apply a dark solvent stain then you may have to go finer, especially if you have not always sanded with the grain. Compare that with some wood like a Rosewood such as Dalbergia Melanoxylon- here you can see the scratches from 600 grit....Or one of the New Zealand softwoods such as Rimu or Kauri, which require a lot of fine sanding before they feel right.
When you know the wood then you get the answer to your questions, I believe.
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