I am well aware that to achieve an even better result from sanding, one should slightly moisten the wood in order to raise the grain following your final sanding and then go back lightly to remove any predominant fibers. However, on my current project, I am attempting to stick w/ a scraper unless necessary. Therefore, my question is whether it is recommended to scrape, moisten, and then either lightly sand or scrape afterwords to remove any raised fibers. If the wood is scraped in the first place, will their still be fibers that raise from moisture? Will this help? Opinions?
Thanks as always!
“100 Years” — scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work — “If anything I make fails in the first hundred years, bring it back, and I’ll take care of it. After that, there will be a small charge. (Original purchaser only)”
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As I understand it, sandpaper abrades the wood which is why you get the fibers. A scraper cuts the wood cleaner and does not need moistening. Also, when sanding, the dust is forced down into the pores and that is why you get a nicer, "glowing" result when finishing a scraped or planed piece.
Anyone who wants, jump in and correct me if I am wrong - - Please.
That makes sense...Thanks
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
I've found that scraped surfaces, show more raised grain than sanded surfaces, especially on woods with open grain, or that are stringy by nature ( like some mahogany). I too like to use as little sandpaper as possible, but it is a necessary evil. I scrape then sand with 220 followed by 320, then dampen the wood and resand very lightly with 320. For the most part I resort to scraping only on veneer. The quality of my finishes jumped dramatically when I acquired a york pitch smooth plane.
Rob Millard
The most recent issue of FWW has a feature article comparing the 3 alternatives: planing, scraping and sanding. The author concluded that he could detect little difference in the finished product applied to different lumber.
Personally, I tend to use a mix of techniques that are dictated by the type of wood I'm going to finish. I can't state with authority that the following is true but highly burnished wood surfaces are perfect for penetrating oil finishes but build finishes such as lacquer, varnish and shellac require a slight amount of raised fibers to anchor the film coat. If this is indeed true, that really does argue that there is an appropriate place for all of the wood prep techniques.
Those film finishes will adhere quite well without raised grain. The reason not to sand surfaces under these film finishes down to burnishing fine grits is just that it is pretty much a waste since you won't see the difference between 220 grit and 400 grit under 2 coats of varnish. (Unless the scratches are highlighted by a pigmented stain, but that's a different issue entirely.)
Here is some info that relates to your question.
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.. 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 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. 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.
Another point is that "raising the grain" had little value unless you are applying a waterbased stain or finish. The "grain" is really little nibs of wood that swell up when wet. They will swill up whether wet with water or any other finish or sealer. It's just that they become most prominent when water is applied.
In other words, all liquid finishes will somewhat "raise the grain". This is the primary reason that the first coat of finish rarely feels smooth. The wood nibs have become swollen with finish and are now sticking up. Finishes must be sanded after the first coat to remove these nibs and subsequent coats of finish will be applied to the finish, not the wood.
So, my practise is to never worry about "raising the grain" unless using a water based dye. I don't "raise the grain" if I am going directly to the clear waterborne finish. I let the finish raise the grain and then lightly sand it. It accomplishes the same thing as using water but gets you one step ahead in the finishing schedule.
Interesting comments Howard. Did you publish any of your test results or were they simply for use at your job?I guess you have simplified my process, at least when not dealing w/ water-based products. Thanks!
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
The shop produced custom and semi-custom furnituer for a "carriage trade" NYC interior designer. His firm had very strict requirements for quality. We did lots of testing of adhesives and finishes for the 7-8 years we had a relationship. We had no reason to publish the results but we were under no real restriction either. We did other custom work also including work for a couple of custom yacht builders.
The first half the the write-up is something I put together for a small woodworking club I used to belong to and consult for. It was published in their newletter about 15 years ago.
Howie.........
Edited 11/18/2005 5:31 pm ET by HowardAcheson
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