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I recently made an end grain cutting board. Unfortunately I didn't pay enough attention during the glue up and I have a couple of knots/knot holes that go through the board. The largest hole is roughly 0.5" in diameter on one side and 0.125" on the other. The board is ~1.25" thick.

Typically I pot these kinds of holes with super clear epoxy and occasionally add saw dust or something if I want to match the wood color. Given the application, I'm hesitant to use any old epoxy. I've read a lot of threads (including on this forum) about different food safe adhesives/finishes/etc. I've seen everything from

all epoxies are food safe once fully cured

to

never use epoxy

Other threads mention PVA glues, CA, and hide glue. I don't think any of those are good solutions for filling a hole as large as the one I'm describing.

It seems like FDA CFR 175.300 is the most stringent regulation for food safe coatings/adhesives. Wondering if there are any recommendations for a clear potting compound (doesn't have to be epoxy) that conforms with FDA CFR 175.300 and would be good for this application.

  • possible duplicate of What type(s) of glue can I use on wooden kitchen utensils and devices? – Matt Aug 24 '15 at 18:20
  • This question is looking for more reliable justification. Perhaps a bounty on the other question could be in order? – Matt Aug 24 '15 at 18:29
  • I don't think it's a duplicate. I'm specifically looking for a potting/filling compound rather than just an adhesive. Titebond III, for example, is known to be food safe, but it will do a terrible job at filling a knot as I described. The accepted answer to the other question mentions hide glue and CA as well. Both would not do well in this application. – Doov Aug 24 '15 at 18:36
  • leave one hole in a corner as a place to hang it from? – ratchet freak Aug 25 '15 at 8:48
  • Have you considered using wood itself as a "filler"? If you can cut a circular hole/cylinder, clean, over the knot, (or carve a square mortise) and fill it with a wooden plug / dowel, you might be able to turn it into a pleasing design element -- possibly even using endgrain of a completely different color. – ww_init_js Dec 28 '17 at 0:52
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all epoxies are food safe once fully cured

This may be an overstatement.

Food-safe epoxies do exist. In order to be considered "food-safe," the ingredients need to meet FDA CFR 175.105 & 175.300 (in the United States, at least).

McMaster-Carr has some for sale. Permabond makes some.

West Systems, another well-known epoxy maker, specifically states that

[t]o date, none of Gougeon Brothers' epoxies meet FDA regulations or any other drinking water certified approval.

To me, this means that nothing they have is strictly food-safe. However, they also state the following:

What about the builder who weighs the risks and decides to go ahead against our recommendation? For the homebuilder it is a personal choice. If you build a potable water tank, follow the general guidelines noted above; in addition, you may want to install an in-line filter to help remove any possible extracts and odd tastes.

Here they recognize that people will use their product against recommendations and give a couple of suggestions to reduce the chance of any side effects.

There may be other manufacturers that have food-grade epoxy, but these are what my initial Google searching have unearthed.

Given the application, I'm hesitant to use any old epoxy.

Let us also consider the usage of a wooden cutting board. They are not submerged in water for a long period of time (at least, they shouldn't be). Most shops are pretty conducive to a good curing of the epoxy resin. Generally, foods are not particularly acidic, though epoxy's resistance to acids may be found on this webpage. It is possible that chopping with a knife could dislodge fragments of the epoxy, which could be ingested. At his point, it is really up to you, as an individual, whether you can tolerate this risk of possible side effects (personally, I probably would if I reviewed the product's MSDS sheet and also read other users' reviews of the product for food-grade utility).

  • Thanks for the response! I saw that mcmaster sells 1.4 oz packets of "FDA approved" epoxy (since it's mcmaster they don't tell you what you're actually getting, but I suspect it's a masterbond product). They are really expensive, but I suppose doable. The biggest issue I have with that part is that it's orange/amber in color, which would look pretty ridiculous against the maple board. Is there a reasonable way to color match? Dye? Sawdust? – Doov Aug 25 '15 at 17:18
  • You might try a TrueTint dye and just make it black. I don't know that you'll really be able to change the orange color, so making it black might be the least offensive course of action. – grfrazee Aug 25 '15 at 17:22
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    @Doov, you can colour epoxies in many ways, sawdust or sanding dust will of course colour the mixture to some degree but any dry powder in fact can be used, including wheat flour and other things around the house (e.g. talc and dried coffee grounds). You can also colour with actual coloured powders, i.e. dry pigment, and the best white is titanium white which is non-toxic enough to be used in pill coatings so should be fine here. Maple sanding dust + a bit of white pigment should get you a pretty close colour match. – Graphus Aug 25 '15 at 17:54
  • @Doov, I meant TransTint dyes. Sorry for the typo. – grfrazee Aug 25 '15 at 17:57
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Personally I'm of the belief that epoxies are safe for direct food contact (once fully cured) without specific information to the contrary, based on basic principles. That's not to say I would use any old epoxy as a surfacing for something like a drinking vessel, but I'd be perfectly happy with virtually any commercial wood finish for incidental food contact.

In relation to your boards presumably you want to take a more conservative position and there are three possible fixes I think you should consider:

  • leave the holes
  • fill with glue and sawdust/sanding dust
  • plug with wood

A hole through a board at first glance would seem like a terrible health hazard but in reality it shouldn't pose much of a problem if it's A, through the full thickness of the board and B, not too narrow in diameter. To begin with nothing is going to get lodged in there and not be clearly visible and secondly it would be easily dislodged; in effect, there's not much difference between the sides of the holes and the flanks of the board. But obviously there's an aesthetic issue here and holes through the board could be considered unsightly.

Even if using epoxy you don't fully trust, the sawdust/sanding dust fill is clearly much safer purely on the basis of there being less epoxy present (far less, the dust component could be the major constituent). But to err even further on the side of caution you could use a waterproof woodworking glue already approved for use on cutting boards to bond the fill.

Plugging with wood is clearly the safest option if viable technically, since at most you'd be left with a glue line at the margins of the plug which is not much different to the glue lines already present in the board.

  • Thanks for the response! My understanding is that something like titebond III (e.g. waterproof woodworking glue) makes for a pretty bad filling compound. Do you think it's realistic to plug a hole of the size I'm talking about with titebond III and sawdust? If so that seems like a pretty good option. The reason I want to plug the hole is three fold: stability of the board, functionality, and aesthetic. As it is I can easily imagine the hole getting bigger quickly with enough chopping/cutting (unfortunately the knot hole is almost center center). That's bad for obvious reasons. – Doov Aug 25 '15 at 17:12
  • Aesthetically I think it would look a lot better if the hole were plugged. I suppose option 3 is doable, but I'd rather avoid it if possible (extra work, more possibility to make things worse, etc). – Doov Aug 25 '15 at 17:13
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    @Doov, FWIW I've plugged holes much larger than 1/2" diameter with glue + sawdust, Admittedly this was not for a cutting board but the hardened fills seem extremely robust. Done using epoxy they're even tougher, so much so in fact that they pose some difficulty to plane or chisel edges. As for plugging with wood, if the hole is close to the size of a commercial dowel you could just glue a short section in, then saw nearly flush once the glue has hardened, followed by paring away the excess with a sharp chisel before sanding to do the final flattening. – Graphus Aug 25 '15 at 17:44

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