General Finishing Question

The Achilles' Heel of Luthiery
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Diane Kauffmds
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General Finishing Question

Post by Diane Kauffmds »

I understand that one does not want to sand a piece of wood, that is going to be stained, too finely, so that it will accept stain, but what about unstained wood? Can you sand a guitar, which isn't being stained, too finely, prior to pore filling and shellacking? If so, how fine should I go with the sandpaper?

I went to 600 grit with the practice project guitar, and it seems to have accepted the finish just fine. I want to make 100% sure that I can go that fine, with my OM build.
Diane Kauffmann
Country Roads Guitars
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B. Howard
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Re: General Finishing Question

Post by B. Howard »

Yes, prep sanding too finely can lead to problems. Most notably finish delamination, or peeling. These problems usually don't show up immediately but rather down the road (sometimes a few years) after the wood has moved seasonally. The finish needs to be anchored to the wood surface. If the wood can move under the finish without holding onto the finish the two will separate at some point.

Some finish materials such as penetrating drying oils can hold onto a surface with a finer prep texture while modern high solids coatings need a fairly rough surface to bond too. My standard prep sand is 180 for open pored woods like rosewood or mahogany and 220 for closed pore wood like spruce or maple. It should be noted I do all my prep sanding by hand. Machine sanding will tend to close up the surface of the wood quicker and I would consider stepping back to 150/180 if I was prepping with a RO or DA sander depending on my technique and freshness of the abrasives. I have used this same prep under all my wood finishes for many years without issue.
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tippie53
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Re: General Finishing Question

Post by tippie53 »

I am with Howard
180 is a fine as I go
John Hall
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Diane Kauffmds
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Re: General Finishing Question

Post by Diane Kauffmds »

Thank you. 180 it is. I only hand sand also; no sanders.
Diane Kauffmann
Country Roads Guitars
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Zen
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Re: General Finishing Question

Post by Zen »

Is the 180 grade sandpaper in USA different to the European 180 ? I think I read somewhere that there may be a difference.
To me the 180 over here in Europe sounds very rough and 320 is usually what I use
Rusty
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Ben-Had
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Re: General Finishing Question

Post by Ben-Had »

Zen wrote:Is the 180 grade sandpaper in USA different to the European 180 ? I think I read somewhere that there may be a difference.
To me the 180 over here in Europe sounds very rough and 320 is usually what I use
Rusty
I don't find any significant difference between P (European) and Cami (US) until about P320 grade.
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David L
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Re: General Finishing Question

Post by David L »

I find it best to listen carefully to what Brian says!!! The only time that I sand finer than 220 grit is when I want to achieve a high natural polish that will not receive any type of finish. This is not always possible on some species of wood and I'm not even going to go into the aspects of that for obvious reasons.
Here are some pictures of a magic wand (and it really is magic of course) that I made for my daughter who's a huge Harry Potter fan (and that's an understatement). The handle is a piece of African Blackwood and the other wood is Sapele. For the handle I went through all the grits progressively all the way down to 12,000 Micro Mesh sandpaper. There is no finish applied to the Blackwood. To get it to look like this I spent quite a few hours and a lot of elbow grease, but hey, It's for my daughter so it was worth all the work. The Sapele part of the wand will get Minwax tung oil finish.

David L
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