Question
I have two large cross-sections ("cookies") of Siberian elm. I have given both many applications of Pentacryl to prevent cracking as they dry. Per instructions from Preservation Solutions, I have boxed both slabs up and stored them in my cool, dry basement to dry slowly.
The problem is that the slabs were in my warm, humid garage, often covered in plastic, while I applied numerous coats of Pentacryl and waited for it to soak in. During that process, a mold or fungus began to take hold. I have sprayed the wood with more and less diluted bleach to kill the growth - enough to lighten the wood surface visibly. Today, I checked the slabs again after a week or so and the fungus is back.
See the white fluff on the images below. Does anyone have any suggestions how to get rid of the fungus/mold? I'm hesitant to keep using bleach for fear that I'll damage the wood too deeply to retain its nice color. Will an alcohol application work? Are there any other, non-bleach products?
Forum Responses
(Sawing and Drying Forum)
From contributor X:
Plane them to the extent the mildew has penetrated, treat with fungicide/mildewcide and reseal. The mildew fungii may return since it's probably penetrated the cells deeper than you can plane and treat, but it will slow it. If you can keep them in a cool dry place it may not return. Seal them very well though so they don't dry too rapidly.
You may have to repeat this process more than once. Once they are dry, if there are stains you don't want, you can test a small area with Kleen Strip WB-19 two part bleach. Test both sap and heart to make sure it doesn't bleach out the color you want to keep. Every species reacts differently to bleaching. Most heartwood will fade out but not all. It's worth a shot.
I've seen products like Tim-Bor or BoraCare, but they seem more targeted at the construction world than the furniture world. Do I need to be concerned about fungus or mold possibly growing within the wood, or just the surface stuff?
Sealing the wood is not the recommended process for Pentacryl. I'm told that once the wood is well soaked-through with the solution, it should be boxed up in cardboard and set to slowly dry in a cool place, with a relative humidity of 40-60%.
I've been using the WB-19 for going on six years and I can vouch that the pieces I've used it on have remained the same. This ERC beam was felled in a dry riverbed where the sulfur content was very high. The sap on these trees was quite yellow. I apologize for not having a before pic for this but you've all seen the yellowish looking sap in some ERC I'm sure. ERC is not a species that you want to bleach the heart as it will fade dramatically, but the sap responds very well in my experience.
This picture is about three years old and the sap is every bit as white today as in this picture. One of our sons carefully applied the bleach to the sap only. You can see it is still a bit blotchy with light yellow but not even close to the pre-bleach color which was unacceptable to the whole family. I had to get it white or log and process more trees. We have numerous ERC bar tops and flitches throughout our home that came from this stand of trees and they are all still just as white as the day they were bleached.
The cookie on the left was about two inches from the one on the right in the log. IOW there was another cookie between them but I selected these two to work first. The one on the right has been processed and has the first coat of shellac on it. But it looked the same as the one on the left prior to bleaching. The shellac gave the sap a little amber back, but you can clearly see how well the bleach has hidden most of the stains. This bleaching effect will not fade unless the cookie starts to mildew again or fungus etc. gains another toehold.
Like everything in woodworking, not all techniques can be used in every situation, but everything has its place. Bleaching works for me in certain situations so I use it. Some others do also but still others will turn their nose up at it (not inferring to anyone here just speaking in general). I just thought I'd mention it because I know most woodworkers aren't aware of the product and potential benefits of using it. I don't like to use biscuits or pocket screws, but I can understand why others think I am crazy to avoid using such technologies. If you do ever try it, make sure you have a defined goal that you're trying to achieve with it and as stated, test both sap and heart in an inconspicuous area.
I have not worked with elm, but I have a lot of maple and it just loves to grow that same looking fuzz after a while of spalting. It degrades perfectly good wood into a papery substance if given time. I think if it were mine I would find a way to hinder such a favorable environment to fungus growth, starting with opening the wood to a more open air supply.
The second effect of bleach is that it changes the wood color (bleaches it). This effect was illustrated by Contributor X in his posting. Note that such bleaching will minimize the grain appearance so it must be used carefully. Further, bleached wood should usually be neutralized or well rinsed.
Based on your earlier comments, it sounds like this white fuzz mold is a surface-only issue, but the fact that it's there indicates a very high likelihood of other, discoloring molds within the wood. Is that about right?
Do I have treatment options to stop or remove any interior molds that may be present? Keeping in mind that this is a big end-grain cookie that will crack very easily, a treatment that doesn't require rapid drying would be preferred, but it sounds like that may be a pipedream.
If the options are between (a) throwing this thing in a kiln or otherwise rapidly drying it and therefore almost certainly causing it to crack, or (b) treating the surface mold and keeping it in a cool/dry place to let it continue to dry slowly, and then seeing what I end up with when I get to planing and surfacing the piece, I guess I'd have to opt for (b) and hope for the best and deal with the issues when I see what they are. Is there a practical, dependable third option? Thanks again for everyone's time and expertise.
I’m not knocking Pentacryl - it may work in some situations but I didn't tinker with it for long. The best way is if you can get it vacuum dried. That will definitely minimize cracking and stains. I don't think any of my cookies would have cracked had I moved them to Den in a timely manner.
I don't know if having only between 1.5 to 4" of long grain is making the difference, but that's the only thing I can think of. The radial or tangential shrinkage isn't changed just because there is less longitudinal, and longitudinal is the least of them anyway. I can't explain the scientific reasons why cookies seem to have less destruction (to my observations) being dried in a vacuum. Some still crack but not nearly as many or as bad. That's been my experience.
You have to have some kind of benchmark for comparison, and seal and air dry is what I use for comparison. Most turners like to get them green anyway, so I just seal and stand them upright on plywood pallets, in a lean-to I have to keep them out of the sun, with several inches of space between each. My avg. humidity is between 70 - 80% so that helps. I couldn't do this in Yuma AZ they'd all crack wide open early and often.
Out of the eight cookies I've had dried in the vacuum kiln, only two cracked that were not already cracked, and the cracks weren't as bad as they would have been IMO if just sealed and dried, based on my experience. I’ve never transported any of the cookies to the kiln as fast as I should have. For various reasons I have allowed other things to take priority and time flies around here pretty fast.
I only send cookies that really have something going for them. My business model dictates that sealing green and stacking them is most profitable because that's what most of my market demands. Next time I cut some that are exquisite, I have vowed to stop the circus and get them to Pennsylvania immediately. They have emphasized the need for me to do this and next time I will. Out of the last five, three did not crack at all and two of those were quite thick. One was a 24" diameter cookie 4" thick and it did not crack. The pith barely showed any checking. That's not common at all.
The other two methods that I have also noticed significant success with are the alcohol method I mentioned, and for cookies small enough for the microwave, I have combined the alcohol bath with microwave heating and periods of stress relief between. Don't ask me to explain this in detail it's more like voodoo and flying by the seat of your pants. I have success with it because I wrecked about a dozen before I got the knack for it. Works great for pen blanks and other small blanks as well, but the smaller end grain cookies respond very well to this method.
If given the choice between making a living drying pecan cookies and beating my head against a concrete wall I'd have to give it some serious thought before deciding. Try the alcohol bath method. It's bound to help, but pecan is difficult to dry under the best of circumstances. There's no silver bullet, but I am confident that getting them dried in the vacuum decreases checking significantly, and I haven't even given the vacuum a chance to show its true potential IMO.
In any case, a basin like that would have help with the Pentacryl, too. Submerging for a few days and then immediate storing would probably have significantly reduced the likelihood of mold taking hold, as opposed to leaving them warm and wet under plastic in my Chicago garage while I applied multiple coats of solution.
For drying, you're right. The prescribed method is to rest the slabs on edge, inside a cardboard box, in a cool dry area, to minimize airflow. I custom built a crate out of 2x4's and then sealed the whole thing in corrugated cardboard, and placed it in my basement. Of course, the box does get opened periodically so that I can get to the mold to treat it, but then it gets sealed up again to rest. Theoretically it will take three months of drying per inch of wood thickness.
Everything seems to be going fine for now. No cracking yet, but it's only been a few weeks. I'm going to get a moisture meter to track the drying progress. Stay tuned.
