Wet and Dry Streaks in Air-Dried Slab Walnut

Sawmillers troubleshoot moisture and color variations in big slabs of partially-dried Walnut. December 6, 2009

I've bought some air dried salvaged walnut recently and found some light, wet streaks once I planed it. The darker parts tested dry enough, but the light parts are around 30%. Can anyone suggest a San Francisco Bay Area place that might be able to help finish drying this? Does anyone have a shop solution? There's only about 12 slabs, planed down to about 1.5". Will the light streaks get dark?

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Forum Responses
(Sawing and Drying Forum)
From contributor H:
I suspect what you have is the beginning of spalt, AKA rot. Hope you did not pay a lot, because it looks like firewood.

From contributor N:
Firewood!? I could sell a hundred of those slabs.

From the original questioner:
Tell me more. I've never seen or heard of this problem. It's only in the core, and it doesn't seem any less dense, just wetter. One client likes the look for some coffee tables. What will happen to them over the long term?

From contributor S:
This is the result of partial drying while in log form. The light greenish color is wood that has not started to dry at all; the darker wood is well on its way to being dry. If you opened up a kiln dried board that had wet spots in it this is what it would look like. In time the lighter areas will darken and catch up with the rest of the wood, mostly. Sometimes there will be a slightly discernible color difference when completely dry. I cut lots of big walnut and I see this a lot, mostly in black as opposed to other species of walnut.

From the original questioner:
Thanks, I hope you're right. The slabs looked fine until I cut them and planed them, so it didn't look like an existing issue. Is spalting generally an issue with living trees rather than cut trees? The wood looks really great (except for the light parts), so I'd prefer to deal with the light spots in the finishing process, and design to accommodate for some shrinkage, unless anyone thinks I'm setting myself up for disaster. I have deadlines with major corporate clients and live edge walnut isn't always available in these parts.

From contributor S:
There is no spalting in the walnut pictures you show. Only the sap in black walnut would spalt. Any wood that is susceptible to spalting will spalt at any time under the proper conditions, i.e. moisture/temp/spore load/oxygen/food source. You will have to dry your wood, or at least enough surface depth to case the slab before you can put a finish on it, and when you do that most if not all of your color differential issues will be resolved.

From contributor T:
Back to the original question of a kiln in your area... There are listings on this site at:
Sawing and Drying Directory

From contributor M:
The light green areas are what the entire board of freshly cut walnut looks like. I agree with the other post that the wood has started to dry while still in the log form. Place the slabs into a stickered stack in your shop. Make sure that there is plenty of space all around the stack and let the slabs finish drying. Monitor the moisture content of a board in the stack, not the top piece, as it will dry a little faster than the rest. Bugs are only a problem with the sapwood. If you can get the boards to at least 130 F for several hours (after the moisture content is below 10%), you will kill any bugs present in the wood.

Walnut is very forgiving to dry. Oregon white oak is on the other extreme. It requires slow careful drying, but both woods are well worth the effort. You should let the person that sold you the wood know that it was not completely dry and should not be sold as such.

From contributor M:
One more thing - walnut is highly rot resistant (except for the sap), so spalt, which is the result of fungal decay, is not likely to be found in the heartwood of walnut. This resistance by walnut to decay is due to a very toxic compound known as juglone (5-hydroxy-alphanapthaquinone).

From Professor Gene Wengert, forum technical advisor:
What you are seeing is a combination of heartwood and sapwood. The sapwood, because of the branch, did not convert normally to the dark heartwood. This lack of conversion can be due to some decay fungi entering through the branch stub or due to bacterial activity. The wood will not turn to the normal chocolate walnut color. Spalting will not turn dark heartwood a light color. As mentioned, spalting only affects the sapwood. This coloration has nothing to do with partial drying in the log.

From the original questioner:
Thanks for everyone's help! I'm still leaning towards the not-dry theory. When I cut it in half, it was like a Hostess cupcake, dark near the surfaces and light at the core.

From contributor W:
That yellow/green marking you're seeing is not sapwood and it's not rot. Do not burn your stash. I have some of the same stuff going on in some walnut I've got in the Bay Area. Maybe it's something unique to the west coast, making us, yet again, one of the coolest places to live. This marking will mellow out over time but I've had some pieces keep this color, too. Do an experiment - take a junky piece and put it out into the sun. It'll crack and warp but you'll see the results, quickly. Also works in the microwave but may stink up the house. Where did you get this material? I'm located south of SF, and north of Santa Cruz.

From contributor X:
No, it isn't exclusive to one area. I cut up some BW logs that had lain in a field for 5 years. They all had this exact same characteristic. The logs had checks on the tops but slabbed off nicely. Large areas of sap were punky to rotten and some spalted. They were still well above 20% MC inside.

From contributor B:

Not really an answer, but I find that a very attractive slab. It would make a very nice table just the way it is. Of course it's not a classic walnut look, but it sure is pretty.

From contributor I:
I think your slabs are quite unique and beautiful. I would think they'd be worth more if you could find a way to keep them looking the way they are.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
The streaks are caused by a bacteria found in certain western walnut trees. It is common here in Oregon. We have found that it appears in about 10% of our walnut (we have over 500,000 BF in stock of live edge and sawn edge slabs and boards). The bacteria causes difficulty with drying and streaking in the wood. You will not see it until planing and the wood can be completely kiln dried otherwise. If you leave the wood in sunlight for a while the streaks will fade (1-2 weeks). Many people use the wood as is. There is no rot, deterioration or sap in these streaks. The walnut looks like vanilla, chocolate swirl ice cream and is pleasing to some but not to others. We have not found a way yet to eradicate these streaks. We run 3 DH kilns full time and process quite a bit of this urban salvage western walnut (Oregon black walnut or claro walnut).