Turning Spalted Wood

[David C. Roseman]

The recent posts on some very nice turnings from spalted Sugar Maple, Pecan, Beech etc. got me revisiting the health issue of working with spalted woods. I just turned a small bowl of my own from a spalted Silver Maple log that had been end-grain anchor-sealed and sitting behind our barn for the last year. Technically turned green, I suppose, but much of the excess moisture was gone by the time I split it into half-rounds. Moisture content read about 15 -18 percent at the surface, before turning. I finished the piece immediately with an oil/urethane mixture (GF Arm-R-Seal) to stabilize it. So I've started wondering, once sealed with a fully-cured polymerizing finish, is there any future health risk from the fungus? I've taken a look at some of Dr. Sara Robinson's prolific writing on spalted wood (e.g., http://www.finewoodworking.com/item/...ebunking-myths). This excerpt:

Fact or Fiction: finished spalted wood products should not be placed in contact with food
Fiction! If you dried your bowl before you finished it, the fungus is dormant in the wood. That means that, while not dead, it is no longer reproducing or producing spores. Any current spores in your wood will be sealed in by your finish. There is absolutely nothing wrong with using spalted wood for food items, as long as it is properly dried and sealed.

So now I'm wondering for the future just how dry the piece should be before the fungus becomes dormant? And even if not completely dormant, will it be sufficiently contained by the finish to make it food safe?

David

[Dennis Ford]

I don't believe that a finish will "seal in" a fungus enough to keep it from growing IF conditions are right for it to grow. Not sure what the moisture content has to get down to for the fungus to go dormant but I am sure that 14 - 15% is low enough to stop fungal growth (it probably stops at a higher level).
I turn a lot of spalted wood and have not had any issues but I do not use a spalted piece for food very enough.

[Faust M. Ruggiero]

I wonder if an alcohol soak will kill the little plants or just make them drunk. Perhaps the finished piece can be exposed to heat in a microwave to kill any remaining spores. Maybe a biology knowledgeable turner can tell us how to stop the growth. I also turn spalted wood but have not used it for bowls that will hold food. I wouldn't be afraid to use it, I just haven't. I usually lacquer spalted pieces and lacquer is not the best finish for a salad bowl.
faust

[Tim Rinehart]

While I understand folks want to be 'on the safe side', I think I recall reading alot of what Dr Robinson talked about essentially dispelled most fears of contamination. The human body is a very inhospitable environment for the spores that cause spalting to take hold, and just out walking around in the woods you are exposed to them as well.
My interpretation is that once the wood has been allowed to dry to inside humidity levels, the spores stop their thing. If I happen to eat them, my digestive tract will do things to kill off the spores.
I think when turning/sanding, you need to be personally responsible for not ingesting/inhaling dust, whether pure wood or wood with spalting. I don't believe from anything I've read that makes me feel more concern over the little bit of airborne spores over just plain dust.

[Jim Burr]

Keep in mind that many fungus varieties are spores. Inother words, nothing but extremely high heat kills them. We are given to understand that you are wearing full respiratory protection when turning spalted wood? If the fungus is indeed dead, then whatever finish you choose is food safe once cured. Please remember...the dumbest thing you can do is wear adust mask...just ask any professional.

[Jamie Donaldson]

I have read that moisture content below 18% in wood kills the spalting process, and Dr. Robinson's research is credited with being the gospel for human/spalt host interaction.

[Seri Robinson]

Hello everyone. Dr. Spalting, reporting in. I thought I might stop by and clear up a few things. First off, I did an article in American Woodturner about health and safety on spalted wood. You might give that a go first. You'll want the August 2011 issue, pages 44-51.

But there are a couple of things I'd like to comment on / questions I'd like to answer.
- it is true that dust masks don't do much, but don't confuse a Wal-Mart dust mask with a NIOSH 95 or higher mask. Those are relatively inexpensive and disposable.
- If the whole idea of fungal spores REALLY bothers you, you could do several things.
1) spray the bowl down with 91% isopropyl alcohol and then a 10% bleach solution. This is how we kill fungi in the lab. Also, the spores aren't generally going to be INSIDE the wood, so it's really only the surface you need to worry about.
2) microwave the bowl. If you do it long enough, that should kill most things
3) turn a large blank into a small bowl, so no original surface area remains. No surface area, no spores, unless the piece is still wet. So dry it and then turn it (which is not an ideal situation, but hey,
YOU'RE the one who's afraid of spores...)

- dry the piece down to about 12% and your fungus will die in a few weeks. Spores can technically keep forever. If the piece got wet again for an extended period of time you could reactivate the fungus, but we're talking days, not hours. So don't leave a spalted wood cutting board in dish water overnight and you're fine (and don't do it with any wood cutting board anyway).
- there are fungal spores on everything. This includes every piece of wood ever. Spores are in the air. You're breathing them in right now. Just because a piece doesn't look spalted doesn't mean it doesn't have fungus on it.


I think woodworkers are too concerned about the wrong thing on the spalting front. Zone lines (the black lines) and white rot are made mostly by basidiomycete fungi. Some of the most prolific spalting fungi, like Trametes versicolor (Turkey Tail), are edible (but they'd taste gross). And unless your spalted wood starts making mushrooms, it wouldn't have any spores on it anyway because these basidiomycetes aren't making spores in their hyphal state.

If I was going to be paranoid about spalted wood, and obviously I'm not, I'd be more concerned about eating from an unfinished bowl with a lot of pigment in it. We don't know a lot about those fungal pigments. And while they do appear to readily bind to wood, if one were to soak a spalted wood bowl in ethanol for some reason and then eat out of it while the ethanol was still drying (do you see how far I have to reach to make this an issue??), one might ingest some of the pigment. What will the pigment do to you? We don't know. If one of you wants to fund some research where we force feed rats spalted wood and then see what happens, by all means contact me. Until then, just put a finish on your wood and stop worrying about it.

[Roger Chandler]

Great information, Dr. Robinson........thank you for sharing it!!!

[Jeff Gilfor]

I'm an anesthesiologist (MD), so know a thing or two about lungs, breathing, and what you shouldn't be sucking into those gas bags in your chest.

First, everything Dr. Robinson said is spot on.

Next, the two issues with ANYthing you inhale are:
- Is it a respiratory irritant, and does it have longterm effects; and,
- Is it infectious, and can it grow inside of you and cause problems.

The first issue is likely the more important when it comes to woodworking.

Woods contain silica; some more than others. Silica dust is known to cause mesothelioma (a REALLY bad incurable lung cancer). Anyone sanding heavily silica content woods regularly (like Teak) should be wearing an N-95 level mask. These can be purchased on-line in boxes of 10-20. Not too expensive, and they are disposable. We use them all the time in the hospital when caring for patients with known or suspected TB.

Fungus spores (viable or not) can also irritate the lungs. Sometimes they can get trapped inside and cause the body to attempt a defence against the irritant. This can result in something similar to pneumonia (it's called pneumonitis), and can be quite bad, especially in the elderly and otherwise infirm.

Viable (live) spores can be even more problematic, in that they can set up housekeeping inside your body and have a nasty tendency to burrow through stuff with thier roots. This can cause all kinds of badness, incuding but not limited to, deady bleeding in the lung. Also, if they get into the bloodstream, they can travel to other fungus-friendly spots, like your brain. As you might imagine, a fungus in your brain is not good.

Not all spores, alive or otherwise, are able to live inside of humans. Some requires an environment that is different than what our insides can provide. Also, some are able to be tackled by the immune system.

Bottom line is:

Our lungs are designed to breath air. Smoke, dust, water, burbon, and food inside the lungs are bad!
Longterm exposure to irritants of any sort will cause the body to react to the irritation (like when your watch rubbing against your wrist day after day causes a callous). Callouses in your lungs are obviously not optimal. Sometimes, the body over-reacts, and you get into real trouble with cancer or pneumonitis.

Higher silica content wood is worse, and Spalted wood CAN be dangerous. Using a good DC with 1 micron filter right next to the sanding station/spot, and/or a N-95 mask are a MUST when working these woods.

Jsut be safe, not scared. Hope this boring lecture helps. Sorry for the length.