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I made a cutting board the other day and while I was inlaying another type of wood into it I made a mistake and cut some holes into the board. The local hardware store had some water-based wood filler which they said are food safe. I do use those fillers occasionally and I can get a good color match.

I understand that "water-based" and "cutting board" doesnt sound like a good idea, but was wondering if it is possible to use this type of filler given that the board will be finished with Tung oil, would the oil protect the filler from water? From previous experience, water-based fillers absorb the oil.

I know that I can use foodsafe epoxy or glue such as titebond 3 and mix with sawdust but would prefer the filler if possible.

OKAN
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2 Answers2

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Water-based doesn't necessarily mean water-soluble. Water is just the solvent used to carry the finish. Once the finish cures, the water-solubility is usually gone.

For example, consider Timbermate Wood Filler. Per the product description,

...Timbermate may react with low grade steels and turn black. If this happens, simply add water and remove it, or wait for it to dry and sand it off.

Basically, while the product is still wet (uncured), it is water-soluble. Afterwards, it must be sanded off, which to me means that water will no longer dissolve it.

Therefore, finishing with tung oil really won't matter in terms of water resistance since the filler is resistant to water once cured anyway.

You can test the water-fastness of your dry filler on a scrap piece to be sure if it will last over time. Just drill some holes on a scrap, fill with filler, let cure, and soak for a few days. You should be able to tell if the filler holds up. A cutting board shouldn't be soaked anyway, so this type of test should be sufficient to test the filler.

the board will be finished with Tung oil

Also, I would avoid tung oil for finishing a cutting board. Please have a look at this thread for further discussion on why it's a bad idea. I'm not certain of the food-safety of pure tung oil, but most products sold as tung oil nowadays have very little actual tung oil in them and are instead mostly polyurethane.

Most people just use food-grade mineral oil and renew it every so often. My previous statement about the finish not affecting the filler's water-resistance still stands with mineral oil.

grfrazee
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  • I don't think that is quite correct. I seem to recall that you can rehydrate most putties even after thy are dry. – tl8 Aug 27 '15 at 03:10
  • Maybe while it still hasn't cured, but once it hardens, I don't think water well re-soften it. – grfrazee Aug 27 '15 at 11:49
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I understand that "water-based" and "cutting board" doesnt sound like a good idea

Water-based doesn't mean that the filler is water-soluble after setting, it could be like with latex paint (UK: emulsion paint) which is quite waterproof once fully dried. But obviously it'll depend on the product.

The manufacturer guidelines aside I would want to do a quick test to check that it is in fact durable when re-wetted, just to be on the safe side.

My usual preference here would be to use a homemade mixture of sanding dust and glue, but I understand that some people would be reticent about that on the surface of a cutting board.

In either case, I think you can expect that the fill won't be invisible since neither can be assured to absorb the oil equally. With commercial wood fillers the fills tend to end up lighter, with sanding dust + glue they tend to end up darker.

the board will be finished with Tung oil, would the oil protect the filler from water?

I think this depends on a few things, perhaps mostly on how wet the board will get in use. Some people don't actually wash their boards but basically just wipe them down, while others will scrub them in the sink and leave them to drip-dry.

It could also be significant whether you're using "tung oil finish" (which is typically an oil/varnish blend, and may contain no tung oil at all) or actual tung oil, often sold as "100% tung oil" or "pure tung oil".

While pure tung oil is reputed to provide very good waterproofing I've seen no actual evidence on just how good this actually is, and while oil-varnish blends are a step up from just oil in terms of water-resistance (because of the presence of the resins from the varnish component) they wouldn't be considered a truly waterproof coating. So again I think some testing is called for.

Graphus
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