Advice on treating moldy walnut slabs?

[Moses Weisberg]

Gents,
A neighbor was kind enough to let me at a black walnut he cut down. I slabbed some chunks, sealed the ends, and stickered them in my basement in preparation for the next time I have some free time to turn. Unfortunately, within about two weeks some mold has developed (see pictures below). Looks like there's a bit on the sealed ends as well. I've heard about applying a borax/water solution. Any other ideas?

Thanks,
Moses

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[John Keeton]

Wood this thick will take years to dry, and it requires constant circulation of air. Your basement probably is not an ideal environment with less than dry air, and little movement. A fan might help, and getting the wood up off the concrete floor.

[Ben Pierce]

Ditto what John said. Also, most thick blanks will eventually split. I wouldn't worry too much about the mold. Scrape it off or use a mask while rough turning. But get the blanks roughed out and drying as quickly as you can.

[Brian Brown]

The mold pattern on these looks like the blanks were stored side by side touching each other. They need good air circulation. Separate them by a few inches, and Like John said, get them up off the floor so air can get to them all around. As for mold removal, a strongish bleach solution will kill it, but it is messy, smelly, and could be dangerous.

[Moses Weisberg]

Thanks for the suggestions, the wood is stickered, and I am out of town for an extended period of time, so I can't easily rough them out (I did as many as I could). Any ideas for something less caustic than bleach? Also, my woodshed is full, otherwise they would be there airing out (good problem to have, I know).

[John K Jordan]

I think houshold bleach is not particularly dangerous. It can be used to purify drinking water.
http://www.cdc.gov/healthywater/pdf/emergency/09_202278-B_Make_Water_Safe_Flyer_508.pdf
The mold might be a bigger hazard.

I buy bleach by the case for farm use. Perhaps the biggest danger is white spots on your jeans from splashes. I do try to keep it out of my eyes.

For treating mold, diluting household bleach 50/50 with water is supposed to work better than straight from the bottle. I spray the solution on the wood then scrub off the mold with a stiff bristle brush, rince with water, then spray on a bit more solution and let it dry. For your situation the fan someone recommended to keep air circulating should help.

After the mold is removed and the surface dry you might coat the blanks completely with anchorseal - that can inhibit mold. We usually coat just the end grain to help minimize cracks as the wood dries but a big blank is not going to dry anyway. I often seal big chunks completely and never had them to mold.

Mold on the surface should not affect the wood when turning. However it can lead to discoloration and rot - and even useful spalting on certain light-colored woods. Not much use in walnut...

Oh, another way to keep green wood "fresh" is to freeze it until you are ready to use it. Freezing hurts nothing (trees in cold climates freeze solid and thaw repeatedly), keeps (sealed) wood from drying out and cracking, and preserves the color. You can ask the other John Jordan about this. Note that cut blanks must be sealed since a freezer is an extremely dry environment. I wrapped a block in plastic wrap and after years in the freezer it was still fine. Some people keep a big chest freezer full then pull out a blank and turn it while frozen.

For shorter term storage just keeping it cold will inhibit mold growth - easy to do in winter in many areas. Mold thrives in warm, wet conditions.

Also, some people submerge green wood in water until they are ready to use it.

JKJ

[Reed Gray]

The mold on walnut never seems to penetrate from my experience. I would make sure there is air flowing around the pieces, but I wouldn't use a fan as that could be too much. Walnut is one of the easier woods to dry, slab wise or rough turning wise.

robo hippy

[Jeffrey J Smith]

I've read that diluted Chlorine bleach does work to kill most of the mold - but it also evaporates fairly quickly and leaves the water behind making a beautiful environment for mold to return to. All it takes a couple of mold spores that didn't get killed to cause it to return. This was born out in practice (at least in my case). I've since been using a boric acid solution - you can get the powder at most hardware stores - it's commonly used to keep roaches and ants away from structures (doesn't kill them, they just won't cross a line of the stuff on the ground). I have a spray bottle and all blanks get a spritzing before going onto the drying racks. It has worked beautifully for me here in the very moist upper left hand corner of the country. The mold goes away and does not come back. I haven't heard of any health/safety issues connected with its use - that doesn't mean there aren't any, just that I haven't heard of any. It also seems to have no ill effect on the blanks.
In this neck of the woods, at least in my shop, mold can be kept at bay by keeping some air circulating around the blanks - all sides. I dry on wire racks with stacked blanks separated by stickers. The boric acid spritz is just insurance.

[Moses Weisberg]

Thank you all for the pointers. I'll try a few different options on the different slabs and see if I can just find some time to rough out the blanks properly.

[Scott T Smith]

The mold is caused by high humidity around the wood. There is no need to remove it; simply put a dehumidifier in the basement set to 40%RH or so and leave it running. Also put a 20" box fan about 10' - 20' away from the wood to keep a very gentle air movement around them. Between the two you should be fine.

[Paul Gilbert]

The industry standard for mold inhibition is isothiazolinone. It is commonly called Kathone which is a Rohm and Haas trade name. It is used on virtually all pressure treated lumber that you find in the big box stores and lumber yards. It is also extensively used as a cooling water biocide (my former trade). For this application a 1.5% is standard. Problem here, I would bet that the smallest quantity that you could buy is 5 gallons and that would last you a lifetime. Also this is really nasty stuff. It is widely used as a preserving agent in cosmetics, but in a concentrated form can cause real sensitization. Once you get sensitized to this even the amount in shampoo and bar soap will cause you to break out with a bad rash.

[Leo Van Der Loo]

Wipe it dry, yes some stuff like bleach will kill what is on the wood now, but as soon that is gone (Like in a few hours) the new mold spores that fall on it will grow again (the air is full of it everywhere).
As long as the wood surface is above the 20% moisture level mold can grow on it, and especially when the there is no drying the moisture will be up there, so plastic or anything else that sits right up against the wood , even anchor seal can have the mold grow right under it.
So that’s why I say just wipe it off and dry, yup up off of the floor to :).

[Aaron Craven]

I had a nice sized bunch of oak, poplar, and hickory logs waiting to be cut into blanks that were so green that they were sopping wet (as was the weather at the time). I put them on some plastic sheeting (to keep the floor clean) and applied anchorseal on the ends until I could get to them, and within about 3 days, all the endgrain was a lovely shade of blue/black; one piece even had a quarter inch layer of nasty black slime on it (yech). When I asked a local turner about them, he told me I could spray them with a 5-10% solution of household bleach and water if it really bothered me, but said it wasn't really unnecessary unless it got ridiculously bad because nearly all the mold would stay on the surface. I did spray them (it really only slowed the mold down a little), but he was right; when we cut them up, the mold had not stained past the surface on any of the pieces. After a couple of weeks, the huge initial rush of water was gone and the mold stopped on its own. The cut blanks haven't shown any signs of molding since.

[Dan Hunkele]

After it is cleaned off with bleach and dries spray it down with some peroxide. Peroxide will kill mold deeper into the wood.

[Prashun Patel]

I get that all the time.
It's caused (for me) by poor air circulation.

I'd scrape it off, and spray it with household bleach diluted in water.

For me, it's important to remove or kill the surface mold because when bandsawing or turning those into round, I'm afraid of setting all that stuff airborne or going into my dust collector.

I'd rough them out. They appear to be aggressively spalted. Hope they're still usable.

[Leo Van Der Loo]

I doubt that Black Walnut would spalt in a couple of weeks, and I will have to see the first piece of Black Walnut that has spalting in the heartwood, if there is any, it is in the sapwood only.

As for the mold spores they are around everywhere, you don’t have to be afraid of them, you are inhaling them as we speak, and yes they do get sucked up by your dust collector, if the dust is wet at more than 20%, I doubt that very much, as a dust particle would dry almost instantly going through the air, than mold could start growing in your dust collector, never seen or heard of that though :)

[Aaron Craven]

My dust collector is awesome. It picks up everything. :D
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[Leo Van Der Loo]

My dust collector is awesome. It picks up everything. :D
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Mine works well also Aaron, but I rather use the leaf blower :D ;)

[Aaron Craven]

Mine works well also Aaron, but I rather use the leaf blower :D ;)

Ooh... leaf blower!
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