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Just finished the binding and purfling on guitar #1 and it went better than I expected. I do have 2 places where the purfling channel is maybe 0.5mm wider than it should have been, and I have a gap between the purfling and the soundboard. Would filling that gap with something black be an appropriate solution? Titebond mixed with black sanding dust from purfling cutoffs?

So, was this a result of the herringbone not being held in position when it was glued? If that’s the case, perhaps that section can be loosened and reglued, after carefully cleaning out the dried glue in between. How you loosen things will depend on the glue used.

No, I think the purfling channel was too deep, but the binding channel was correct. Therefore, when I taped and wrapped them, the binding only went in so far as the binding channel, so there was nothing pushing the purfling any tighter.

Unfortunately, any gap filling will be visible. Glue/sawdust is hard to match the overall color, since it dries darker than the source wood of the sawdust. (I select a real light clothespin, which is lighter then the spruce). Certainly experiment with different recipes on some scrap spuce.
Less conspicuous would be crafting a sliver of spruce, matching the grain orientation. Fabricating that will be difficult, but will give the best result. Ideally the sliver will be slightly oversized with the sides tapered to fit the present gap. Then gently tap in when you glue it.

I agree with Kevin's suggestion - and I agree it will be tricky. But you might find the right grain orientation in the spruce you cut off when you cut out the top. If you are interested, I experimented with a different repair on a ukulele with a similar gap (on the back of the uke). But in that case, both the purfling and binding were not in far enough. And the patch IS visible. Thread here:

viewtopic.php?f=59&t=9224

Bruce W.

You could try melting a black shellac stick into the gaps. I find that works pretty well.

MaineGeezer wrote: ↑Fri Mar 25, 2022 3:51 pm You could try melting a black shellac stick into the gaps. I find that works pretty well.

I was thinking a fill with something black would be good.

with wood binding getting this to move would be very difficult
Glue and dust usually is problematic as it leaves a color foot print
I use shellac and dust or even duco and dust as they are more finish friendly

Thanks everyone. I’ll give Duco and dust a try. It’ll work out.

Like John said, shellac and dust has become my go to filler for these situations. You can never truly hide it, but you can improve it. Watercolor pencils also can be useful. As long as there is some finish on the area, you can play with watercolor pencils as much as you want and there is no damage done. Good luck!-Bob