micro-plastics in wood filler

[John LaTorre]

Given the attention that's been focused on micro-plastics and their harm to the environment, I am concerned about using the wood fillers that have been a staple in my instrument making. I'm wondering if there is a way to fill open, porous wood without the use of these products, which I understand are basically tiny plastic particles. Luthiers of previous decades (and even centuries) have used other methods than plastic micro-plastics, but I don't see any references to them in the manuals published nowadays. Can anybody help me on this?

[Bob Gramann]

There’s the old-fashioned oil-based paste wood filler that you buy at the paint store. I usually use pumice in the French polishing method. I can’t find the Brune tutorial on-line at the moment, but that’s what you need for this. Robbie O’Brian has a video online where he used wood dust sanded from endgrain with shellac to fill the pores. The Aquacoat filler that I sometimes use has glass particles for filler. The StewMac Colortone (I think it’s really “Goodfilla”) is ground silica or some similar ground earth. There are many choices. The ones I use the most are the pumice, the Aquacoat, and the Goodfilla or Colortone. The fact that I’ve tried so many and don’t stick with any one method demonstrates how satisfied I am with any of the choices. Each has its positive aspects and each has its drawbacks. Enjoy the quest.

[Alan Carruth]

Like Bob, I've used a lot of different fillers over the years: as with finish coats, nothing is 'perfect', and you have to make choices. Over the past few years I've pretty well settled on the French polish fill, using shellac and pumice. It takes a bit of hand work, and more time than some fillers, especially on open pored woods. On the plus side it's very durable (it could well be what Strad used), looks good, and doesn't interfere with other finishes. It also hardens up much faster than the oil/silex stuff you get at the paint store.

The trick with shellac/pumice fill is not to get on too much shellac. I start with a 'spit coat' of very thin shellac, applied with a pad (linen over a wool ball works best IMO). Once that's on put plain alcohol on the pad, sprikle it with pumice, and start to work that into the grain with a circular motion. The pumice abrades the wood, the alcohol dissolves the shellac, and the pad works the 'mud' of pumice, dust, and shellac into the pores. If the surface feels dry and 'gritty' you can add a drop of shellac to the pad. If you end up with mud on the surface you've got too much shellac, which will have to be wiped off with alcohol, which will pull filler ouut of the pores. Pumice is glass, and it's really hard to sand mud away.

Ideally you'll end up with a slightly glossy surface that has the pores filled level. When you come back the next morning it will have shrunk back, and look like you didn't do much. Persist, with more pumice and a little more shellac. After a few sessions you'll get the pores filled in. Lightly sand back to the wood and proceed to put on the finish.

The filler will be somewhat porous, and absorb finish, which will shrink. With the oil varnishes I use it takes about three finish coats to fill out to level. Oil varnishes continue to cure and shrink for three months or more, so ideally you'd wait that long. Sure.... Sand back one more time to the wood, and start building finish.

[Barry Daniels]

I’m a retired environmental engineer. As previously stated by Bob and Alan, the most commonly used pore fillers don’t contain micro-plastics, as far as we know. But the point I want to make is that even if it were true, using it as a filler on a guitar does not pose an exposure risk unless you lick your fingers after using it. In fact, you would be taking the small particles and locking them away into the pores of the guitar where they would never pose a risk of exposure again. That would be a good thing, right?

[John LaTorre]

I’m a retired environmental engineer. As previously stated by Bob and Alan, the most commonly used pore fillers don’t contain micro-plastics, as far as we know. But the point I want to make is that even if it were true, using it as a filler on a guitar does not pose an exposure risk unless you lick your fingers after using it. In fact, you would be taking the small particles and locking them away into the pores of the guitar where they would never pose a risk of exposure again. That would be a good thing, right?

If all the stuff really ended up on the guitar, that would be a Good Thing. But in the process of clean-up, micro-plastics can end up in the water sources and in landfills, where they migrate into the environment.It's reassuring to know that many of the fillers are silica-based now.

[Alan Carruth]

In the French polish fill the shellac is a 'plastic', it's just a naturally occurring one. So is the linseed oil in the traditional silex/oil filler. Most of the 'modern' fillers just replace those 'natural' plastic binders with synthetics, unless the 'binder' is also the 'filler', as with CA and epoxy.

A friend told be he'd read that plants started using cellulose about 450 million years ago. It took 50 million years for bacteria to figure out how to eat the stuff. All the coal deposits in the world are the indigestible remains of plants that accumulated in that time. Eventually they'll get around to polyurethane and polyethylene too. They've already found a bacteria that can digest poly (ethylene terphthalate).

[Barry Daniels]

Microplastics in a landfill will never end up in the ocean. 99.9% of the microplastics that are currently in the ocean come from Indonesia and that general area where all their trash is dumped into the rivers. I am just as concerned about environmental pollution as anyone but misplaced concerns are very counterproductive. I spent my career cleaning up contaminated soil and groundwater.