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A small chip came off the surface of my piece when I was removing it from the rough stock. (I foolishly removed the piece, which I had just finished CNC'ing, from its rough stock by pressing it, rather than carefully cutting the tabs away - never again!)

Here's a photo of the piece before the repair (and before the finish was applied) - the chip is on the right:chip missing from right-hand side (no finish applied yet)

I decided to try to repair it with a bit of wood glue, which worked OK. However, the finish on the chip is noticeably different from the finish of the rest of the piece, even though both are finished with the same material (mineral oil).

Here's a close-up of the chip as it's being glued - I sanded down the excess that was protruding: chip repair while gluing

And here's how it all ended up looking when sanded and finished - note the chip at the very bottom is a distinctly different color: finished piece, noticeable chip

What should I have done to get the chip to match the piece? I was thinking of rubbing the chip's top surface briefly with mineral oil before the gluing, but I was worried that might weaken the bond.

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  • FYI, mineral oil is not a wood finish per se. It never dries so it should really be considered a surface dressing only. It does wear/wash off and provides very minimal protection to the wood (almost no waterproofing for example) and there are many better choices if a durable surface treatment is desired. – Graphus Sep 7 '15 at 13:47
  • Whoa, thank you, I did not know that! I have been using it because I like the look and the foodsafe aspects, but for this project I'll look into maybe trying polyurethane (can I put that over the mineral oil I've already laid down?) – AKA Sep 7 '15 at 14:31
  • @aka I don't know if that has already been asked here but that is easily another question we would love to answer. – Matt Sep 7 '15 at 18:13
  • Was there a particular reason you needed it a specific thickness? If not, you could have trimmed the top part through most if not all of the chip and refinished. Your piece is very thick, so just a thought. Also, while the chipped portion is noticeable, it's not obnoxious, nor does it stick out like a "sore thumb". – Pᴀᴜʟsᴛᴇʀ2 Sep 8 '15 at 0:17
  • @Paulster2, you're right about just removing material from the top. In this case, there's only about a mm of material on top, as it is covering a Qi inductive charging coil for a phone...thanks for the suggestion though! – AKA Sep 10 '15 at 20:35
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What should I have done to get the chip to match the piece?

The best fix hands-down for something like this is to glue the chip back into place. Assuming the chip can be located of course.

It is important however to strive not to get glue onto the surface of the chip as you're glueing it back in, as it leads to the classic problem associated with glue-contaminated wood when it comes time to finish.

I was thinking of rubbing the chip's top surface briefly with mineral oil before the gluing, but I was worried that might weaken the bond.

You were right to be worried, any oil contamination of glueing surfaces severely compromises the bond.

Where using the original chip is not possible (the chip can't be found or it has been damaged so it won't neatly slot into place any longer) glueing in a piece of the same species would be next best, striving to get a good grain match to the wood in that location. Where the divot in the wood is an irregular shape it can be difficult to get a good edge on a patch so often it's advisable to create a patch with a regular shape (a diamond with the long dimension pointing along the grain is often recommended) and then chiselling out wood to match that. In this case you'd just use a triangle.

If you must use a filler probably the best filler is one made from sanding dust and glue. Now this tip is very common and often in the next breath the person recommending it will say it gives a good colour match*, but generally it does not make a good colour match to the surrounding wood (almost invariably it's darker) and it doesn't stain or finish well (almost invariably ending up lighter). However this can work much better than it normally does: if hide glue is used.

*Some people recommending the wood dust + glue tick may be using hide glue and are just unaware that it makes such a big difference in the outcome, compared to using regular PVA-type wood glues, epoxy or superglue, so they don't know to specify that that is the adhesive they're using.

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  • Thanks for the answer - for next time, am I correctly summarizing your advice by saying: 1) find the chip and glue it in place 2) only then begin finishing, and 3) mineral oil isn't really a durable/lasting finish ...is that about right? – AKA Sep 7 '15 at 14:34
  • @AKA, yes, if possible do exactly 1 and 2 (but if varnishing or using shellac you could very carefully paint a thin layer on the surface of the chip with a small brush to prevent any excess glue from soaking into the surface wood). And yes again, mineral oil is not a finish per se and very much not lasting — people sometimes report that pieces that don't see handling eventually look like the oil has evaporated. About the only thing I think it has any use for is dressing cutting or serving boards, although I don't oil my boards personally as it isn't needed (it's done mostly for looks). – Graphus Sep 8 '15 at 4:27

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