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Post by scorpiodog on Aug 24, 2015 11:31:44 GMT
This may be a dumb question, and if it is, please feel free to tell me so.
Some years ago, I used to do a bit of woodwork as a hobby. I used to have trouble getting a good finish on my bits and pieces of furniture with oil and varnish (but not wax). I discovered (with the help and advice of a pro golfer, believe it or not - they fix golf clubs, you see) that the first coat of varnish or oil would raise the grain, particularly with softwoods, but also some hardwoods (I remember oak as a particular culprit). And no matter how hard you sanded back after that first coat went on, you could never get a good finish.
So the solution was to raise the grain with water first, then sand back, and you'd get a good surface for the finish which with additional coats cut back between could achieve a glassy shine.
Luthiers don't seem to do this, and I can't understand why that first coat of varnish doesn't seem to raise the grain on the spruce and cedar used for most tops.
I've never built an instrument, and, as far as my ambitions go at the moment I don't intend to, but my curiousity is piqued. Can anybody give me an answer? Am I being foolish?
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Martin
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Post by Martin on Aug 24, 2015 11:43:19 GMT
While I do feel qualified to answer this question Paul, I'll await corroboration from my fellow artisans  |
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Post by scorpiodog on Aug 24, 2015 11:48:54 GMT
While I do feel qualified to answer this question Paul, I'll await corroboration from my fellow artisans Thanks, Martin. In fact, it was your thread that prompted my enquiry. |
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davewhite
Luthier / Guitar Maker
Luthier
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Post by davewhite on Aug 24, 2015 17:35:44 GMT
Paul,
Colin may chip in. When I use oil finishes - such as Tru-oil or Liberon Finishing oil - the instrument surface has to be effectively "polished" with no blemishes as the oil is wiped on in thin coats and will show all of the defects in the wood. This is the opposite of other finishes such as lacquer where the wood is not so finely finished as it has to let the finish adhere and it is the finish that is polished up. I use Micromesh up to 10000 grade to do this. As such it would be hard for the oil finish to raise any grain combined with the thinness of the coats wiped on. Also the oil finishes aren't water based whereas most woodworking varnish now is - water as you have pointed out does raise the grain.
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Post by scorpiodog on Aug 24, 2015 19:07:33 GMT
Thanks, Dave. Maybe that's the answer. And I may have adopted the water and then sand approach after I'd only been using water based finishes. I did use Liberon (I tried all sorts of things), but that may have been after I started to use the wet and sand back method. Of course, the acoustic properties of tables and such like are of no moment. What you say is interesting. I've never used micromesh. When I was woodworking it was 2000 paper (I think) and then wire wool.
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R the F
Luthier / Guitar Maker
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My main instrument is: bandsaw
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Post by R the F on Aug 25, 2015 6:46:30 GMT
Something I (vaguely) know about for a change. I'm afraid davewhite's already said it, though. It's water what does it. I've noticed that luthiers rarely seem to stain the woods they use so maybe this is the difference; I'm a french polisher so I have to stain table tops/repairs etc. to match the rest of the piece of furniture and I generally use (or, at least, start with) water stain. The water stain I use is called "ngr water stain", which stands for "non-grain-raising" - but don't you believe it! It's vital to wet the (new or newly sanded - i.e. with new surface wood revealed) wood thoroughly before staining for the reasons discussed above. Once you have raised the grain and the wood has dried, you can gently flatten it again with 240 or 320 grit - but remember not to be too enthusiastic; you don't want to go through to "new" wood again and have to start from scratch. If you are that way inclined, you could go through the whole process again to make absolutely sure there won't be a problem but I find life's a bit short for that. After this grain-raising preparation, you can get on with french polishing only gently flattening between applications (I use 320 when french polishing but it can be a bit scratchy and you can go finer if you want. davewhite and colins seem to know more about oiling than I do so I'll leave that to them. I would say that if you've sanded the wood flat to start with and you're not using anything water-based, then you don't need to worry about all this.
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colins
Luthier / Guitar Maker
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Post by colins on Aug 25, 2015 9:16:13 GMT
Yes you must always raise the grain first and sand back before finishing. When guitar making, this is accomplished usually during the pore filling stage. Both Dave and I use egg white slurry to pore fill, and as this is water based the first application will raise the grain, which is then sanded back as part of the pore filling process. On the top, which of course is usually a soft wood and doesn't require pore filling, I size it with egg white and when dry lightly sand back.
My oil finishing process involves two applied coats, not wiped back, then a light surface level, Liberon is pretty good as self levelling so not much levelling is needed, this is more a dust removal thing. Repeat a number of times and when happy with the finish thickness leave for a week or so then wet sand with micromesh up to 12000 grit. Finally buff out with swirl remover. This gives a lutre rather than a gloss.
Colin
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Post by scorpiodog on Aug 25, 2015 9:33:07 GMT
That's brilliant, Guys. Thanks for satisfying my curiosity. Wood finishing can be a bit of a dark art, guitar finishing doubly so for me, and that's really answered it for me.
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Jo whoever he is.
