"cleaning" spruce?
 

This may seem like an odd question: I'm working on an OM-sized guitar with herringbone purfling on the top. The spruce is pretty pale in color. I thicknessed and sanded the top no problem and the spruce looked great. Now the top is on, the purfling glued-in and scraped.

I am finish-sanding everything before starting my French polishing session and have been running into a problem. The black, fine sanding dust from the purfling (and presumably the edge of the ebony binding) is getting the spruce around the binding "dirty". I typically use a paintbrush to just dust off the top, but that doesn`t seem to get rid of it completely with this one. I've gone back with 320 paper, and even 220, to try to sand it out, which does work, but it`s almost impossible to do a very clean job of it and not hit the purfling at all, which produces more black dust, and... you get the picture.

Not entirely sure what the problem is. It's definitely coming from the purfling. I sealed the top with shellac before gluing the purfling and binding, and scraped all of that off after. So it's not glue residues or anything like that.

Maybe I sanded too heavily at the start and created some tiny grooves that are trapping the fine dust? Can`t tell, because at this point, everything is sanded to 320.

I tried just wiping with alcohol, but it didn`t seem to do very much.

Any suggestions?

Thanks a lot, as usual.

Phil

If you have a compressor, try blowing it off.

If you don't, take the guitar to somebody who has.

May not work, but worth a try.

Yes this can be a problem with spruce. First off i'd say 320 is a bit fine overall, i usually stop at 220 for a FP finish. The finer the paper the greater the likely hood of pushing hard dust from sanding the bindings into the soft spruce as you describe. My last step in prep sanding tops is to use a fresh sharp piece of paper on my large cork lined block and make single passes the whole way across the top in the direction of the grain a single stroke at a time and using a tack cloth to pick up the dust between each stroke.

First don't try to do to much at once.

Tape of all the binding and flat sand your top leaving a border near your taped binding, shellac the top or pore seal by whatever means you intend to seal by.

Expose sections of binding and flat sand from the spruce over the binding so you are drawing the dust away, re shellac the sections, as you work your way around

Steve

Also, try vacuuming out the dust.

I often use ebony bindings on spruce. I usually sand the top to 600 to make the silking "pop". Doing so generates dark dust on light coloured wood, but it easily blows off or vacuums off.

Without seeing your work, my guess is that you have torn fibres in the surface of your top, are using a top with a lot of runout or have coarse scratches left from earlier sanding and that one or more of these are trapping the dark dust. With a strong light reflecting off of the surface of your top, in the areas that are trapping dust, look very carefully at the surface for scratches, torn fibres or more porous looking grain. Conifers, and similarly soft woods, don't respond as well to scrapers, often tearing the surface of the wood. If using sandpaper, one must be careful to sand so that all of the scratches from the previous grit of abrasive are removed by the current grit. That doesn't "just happen" and requires careful attention when sanding. If power sanding, particularly on soft woods, swirlling scratches can be left behind by the sander. They can trap dust.

Thanks for the comments and suggestions, guys. Seems like I've indeed trapped some dust in there. I know what not to do next time... But for this one, since the vacuum isn' t fixing it, can I try to wipe the spruce with something or should I just keep sanding?

Scraper towards the binding.

I sand and seal the top before cutting for binding, and once the binding is done, careful scraping can remove the overhang of the binding without damaging the top.

Sanding isn't a universal solution to all problems. Nor is wiping it with something. Match the solution to the problem. Start by identifying the source of the problem.

Charles,
That is good advice for sure. I figured out what caused this after a lot of careful observation, pondering, and reading the suggestions and comments on this board. I tried different solutions over a week before posting my question here. Was just wondering if maybe anyone had run into a similar situation before and had found a good solution. I am anxious to move ahead as this is my first order.

I know wiping and sanding aren't universal solutions. I've tried blowing, vacuuming and brushing with varying degrees of success, but the spruce still looks a tad darker ("dirty") around the edges in some spots.

Thanks.

Vacuum and brushing usually does it, but in rare cases, I have had to sand in a specific routine to remove it. I normally sand bare wood with 220 grit prior to finishing, but when this happens, I go to a finer grit like 320 or 400. Using clean paper and very light strokes, sand in one direction, moving from the spruce surface toward the edge of the guitar. After each stroke, clean the paper by smacking it with your hand. Even better, vacuum the paper between each stroke. Also, vacuum the spruce frequently to avoid pushing the dark dust into the wood.
Also, you may need to raise the grain to make sure you don't have artifacts from prior sanding with coarser grits.

Great. Thanks a bunch John. Will try this.