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How to stop mildew

Steven Forrest

Steven Forrest

Joined
Dec 23, 2014
Messages
210
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321
Location
Sebastopol, California
Folks,

I have a bunch of green bay laurel that keeps sprouting mildew/fungus. I have cut it back twice, and two days later, it's forming again. I had originally sprayed the blanks with household bleach or peroxide, and neither made a dent. In the past, cutting away the mildew was enough, but not this batch. Suggestions to treat and/or prevent fungal overgrowth on green wood? I am in Sonoma County - it's fairly damp this winter. The wood is in my garage - dry, but ambient humidity is basically the same as outdoors. Nothing is stacked - plenty of air around it. Nothing is wrapped in a bag. Still come the fungi. I did boil the wood - wondering if that somehow promotes fungal growth. Help!
 
Steven Forrest said:
Suggestions to treat and/or prevent fungal overgrowth on green wood?
Click to expand...

Don't know anything about the laurel, but I've had problems with grey stain in light woods like Holly and maple - was told it was from a fungus. For Holly, the advice I got probably won't help where you live but it's to cut the tree in the dead of winter then dry aggressively.

For boards this usually means kiln drying but I'm generally able to keep Holly white if I seal it immediately after cutting it up with the bandsaw, unless the logs got too warm when stored outside for a while - I dry inside the shop in the AC when it's warm. I don't remember anything about boiling "causing" fungal growth, I wonder if the fungus was already in the tree when it was cut, or if it gets into the wood through the cut surface. Is it sealed well? Would it help to disinfect the saw chain?

Do you have the same problem with other species?

Are you boiling the log section? I think the advice I read was to boil an hour or so per inch of wood when boiling roughed out bowls but this was to minimize cracking and distortion. I can check my notes and books.

If I see fungal growth on the outside of the wood it is usually headed toward spalting, which can be a plus sometimes. The tricky thing about spalting on purpose seems to be catching it at the right time before it rots!

About bleach, a scientist friend once told that contrary to what I assumed, bleach was more effective against mold and mildew if it was diluted with water, about 1/2 and 1/2 if I remember. I can ask her again to verify when she gets back but won't be until after New Year's.

JKJ
 
Responses so far:
First of all, I certainly appreciate the advice/attention.
John: I don't think this is spalting stuff. I think it's staining stuff - ugly, blotchy grey. It is dead of winter (for us). I have had this happen with other species, but this is an especially heavy attack. I don't know that I can sort out source - ambient, chain, etc. I forget if I roughed out first or after boiling, but I did boil the wood, then applied bleach/peroxide, then watched it grow over a couple of weeks. Have now cut back twice and it's still regrowing in 2 days. Someone said the hyphae (sp?) may already be all through the wood, in which case, it ain't going away as long as the conditions favor it growing. And those conditions are wet wood, cold, high humidity, and low air flow.
Richard, I do have some two part bleach. I was sort of hoping not to have to go that far, but I guess that's my next move.
Isaac, stuff is all thoroughly roughed. These are not pieces I'm turning to final finish green.
I haven't tried microwaving these. I suppose that could be another path, but I'm not sure they'd get down to dry enough to frustrate the fungus quickly enough to beat the staining, or still avoid cracking.

Still listening. Thanks, all.
 
I think it was Mike Mahoney who told our club some years ago that to at least minimize or at best eliminate mildew when drying roughed-out bowls and such, sprinkle some boric acid in the bag (brown paper bag) with the bowl before closing it up. I can attest that it works (at least for me it does). YMMV. Best of luck Steven
 
Richard Coers said:
Household bleach has a high water content. Buy some 2 part wood bleach.
Click to expand...

I thought 2-part wood bleach was intended to lighten wood surfaces.

Steven Forrest said:
And those conditions are wet wood, cold, high humidity, and low air flow.
Click to expand...

How cold is cold where you live? And how humid?

Here it’s usually around 33-40 in the winter, occasionally down in the 20’s and up to mid 40s.
I keep all processed wood blanks in the shop, sealed, with the temp about 65. The humidity is low year around.
I’m wondering if high humidity might be a problem.

When given the choice I like to cut holly when it’s freezing outside, process inside and seal it immediately and air dry.
if I store it outside or in a unconditioned space it always gets grey stain. But if I turn something from grey-stained holly the 2-part bleach makes the turned surface white. Maple and holly boards/slabs cut on the sawmill and stickered outside to air dry when it’s warm and humid - hopeless.

For rough-turned bowls some people make a simple “refrigerator” or “freezer” kiln, an insulated box warmed by a light bulb or two inside and with holes cut for vents. There should be information on these on the net.

Maybe there is some accessible research out there on fungi which could help. Sari Robinson (Dr Spalt) has done a lot of research on fungi. When I get some time I try do dig through her books. She focuses on inducing fungal growth but probably knows what inhibits it. But it might be able until next week.

Spalted Wood: The History, Science, and Art of a Unique Material​

Spalting 101: The Ultimate Guide to Coloring Wood with Fungi​

Might even be able to contact her and ask. Some people here know her personally

JKJ
 
I have seen some ugly orange molds on the bay laurel, known up in Oregon as myrtle wood. Not sure what to do because the mold thrives on moisture, and dryness will kill it, but that may make the wood crack and split. Since you are by the coast, it will always be damp. I would suggest roughing out the bowl blanks and sealing them. Drying any kind of log sections is always difficult.

robo hippy
 
Following this thread closely. I have some Magnolia roughed out that has the same problem. Very high moisture content, bad mildew. At this point I’m just accepting it as the way it goes, but in the future maybe I’ll give the Boric acid approach a try.
 
Someone on an old forum post suggested spraying roughed out blanks with a citric acid solution. I did try this but but didn't track results; lost in the bowl stack/ pile.
 
If you want to kill mold, try what the professionals use - boric acid/peroxide solution will kill the fungus and prevent regrowth. I live in the upper left hand corner of the upper left hand corner of the country. I think fungus is one of our regional native species. Years ago I was told that chlorine bleach is only a very temporary solution and the water left behind when the bleach evaporated nicely feeds the remaining fungus.

This solution will only last for a few hours so use quickly:

200 ml of 12% hydrogen peroxide, 200 ml of water, and 20 g of boric acid.
I use Baquacil (sp?) from the pool supply stores for the peroxide. It’s 27 percent peroxide, so dilute - a gallon lasts a very long time.

It takes care of the fungus. Boric acid is readily available at most hardware stores. Used extensively to prevent roach infestations and by people who kill fungus for a living. I sprinkle it (dry) around wood that is sitting out waiting to be processed to keep powder post beetles away in addition to spraying all newly roughed bowl blanks while they dry.

By the way - boric acid has been used for many years on bug infestations and for mold/mildew remediation. It’s pretty safe to use with reasonable precautions and as near as I can tell with about a decade of use on roughouts, has no effect on the wood itself. It is also used in dilute form as an eye wash. It does kill mold very effectively.
 
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That’s my understanding - the peroxide adds to the effectiveness, but shortens the useful life of the solution. I usually set aside a day to just rough out and core blanks - at the end of the day or when the roughouts are pulled out of the boiling pot, I mix the solution and give everything a good thorough spray down before stacking loosely so air can circulate for initial drying. If there’s any solution left, I use it up by over spraying everything til it’s gone.
 
Wow - thanks so much folks. Lots to try here. I won't go through each entry, but will definitely try a few of these possible responses. I'll report back to this thread, but it may not be for a few months. I'll keep checking for more suggestions, though.
 
Has anyone ever tried using UV light to prevent mold? I'm thinking of something like a rack in a cardboard box with a top and bottom bulb. Box could be open to airflow, but shade the light.
 
The kind of short wave UV that kills fungi effectively is dangerous to ones eyes and will degrade lots of materials-- at that it really only treats the surface layers. 95% of the mold is below the surface, what you see is only the fruiting bodies on the outside. Getting rid of moisture and fairly high heat are the only things I can think of to kill (or at least stop the growth of) the subsurface hyphae. Getting any kind of chemical to penetrate the several cm (at least) into the wood to kill the hyphae seems like it would be really hard to do short of a fairly elaborate pressure/vacuum pot system.

I'd get the wood as dry as possible as quickly as possible.
 
FWIW, back in the day I used to buy kiln dried hard maple that came from back east through a local hardwood supplier. Occasionally they'd deliver a load with obvious stains from the spacers they used in kiln drying. I don't know if that was mildew or what, but I'd have to have them come back and get it. The material was 4/4 rough, I don't recall how deep the staining went, only that material like that was unacceptable for our use.

This was years ago. At the time they didn't separate the bird's eye from the regular stock. Price was low compared to today. At years end they wanted to clear stock to avoid inventory tax so they would sell it for 50 cents a board foot.
 
Doug Rasmussen said:
Occasionally they'd deliver a load with obvious stains from the spacers they used in kiln drying
Click to expand...

I've run into sticker stain on light woods at my sawmill (no kiln). It would help when the wood was wet and the temps warm to unstack and move the stickers a bit. That wouldn't be practical in a kiln. I'll bet what you got was from them leaving it stickered outside for too long.

Years ago almost every thing was cheap from local sawmills. I found 4/4 oak at 35 cents/bdft and used it to side my chicken house. This was "pallet" grade with a few knots or defects - the better grade were more.

I'd buy walnut, cherry, maple, etc. from one small mill for $1-$2/bdft. When that guy got logs with burls he cut them off and threw them into a corner of the shed by the door - he said he gave them to people with lathes, for no charge. They were worthless to him.
 
On roughed bowls, just let it mildew. Usually it's on the surface and will turn away. There really isn't much you can do about it, and it will stop growing once the moisture content reaches a level that no longer supports the mildew.

I'm not sure if this is universal between species, but I once ran a test and found that mildew will stop somewhere around 18% MC.

=o=
 
I don't know about laurel, but as far as holly goes, years ago someone talking to our club mentioned that holly trees seem to vary as to whether they will gray or not. Experience came from harvesting holly from an orchard with dozens of trees, and some wood would gray, other wood not. They'd get the wood in January or February, which is the best time in these parts to harvest for turning. Might be a genetic thing.
 
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