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Help? Can you identify black stains on this oak?

Started by Ronnie, October 10, 2012, 02:54:53 AM

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Ronnie

Guy brings me some oak logs left over from his log home build. They are kiln dried logs grooved on top and bottom and round on the front. Typical log home log. They dealt me a fit on the mill the pith was no where near center and they had a lot of stress in them. Anyway, that's not the problem. I get them cut up and he wants to know if I will plane them for him. This is not something I usually do but I agree. I ran them through my planer and they were damp after running them through a few times (but kiln dried!). I didn't pay much attention to this until later. I was in a big hurry and got them all ran through before I had to go to my "real" job. I laid them on top of my table saw and ran in to eat and shower before leaving when I walked by on my way out I noticed black stains on the boards from the planer.



 

This bothered me all day, it wasn't very good lumber do to the pith running all over the place. I wondered what caused those black stains. 10 hours later when I got home I picked them up off the table saw and this is what I see.



 

What the heck causes this??? Is it just because the wood wasn't completely dry? These were supposed to be kiln dried logs. They were damp when I pulled them from the planer. I should have never laid them on my table saw. Is this possible from a chemical in the logs?



  


You can see the planer marks on both these boards


 

This pic is where the wood came in contact with the table saw top.

What the heck happened? Any ideas? I don't think it's mold. There is no sign of it in the logs. This mark shows up an hour after cutting - then went nuts when laid on metal.
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thechknhwk

I believe that is tanin in the oak reacting with the cast iron due to the moisture.  Like when you put a steel nail in oak it leaves a black mark and runs down the face.  The first pic looks like skid marks from your planer feed rollers, but that's just a guess on my part.

sawmillhand

wow i have never seen that happen. i was going to say your in feed rollers but after seeing the saw its looks like it did have a chemical reaction to the saw.
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thechknhwk

Found this pdf talking about corrosion and wood.

http://www.npl.co.uk/upload/pdf/corrosion_of_metals_by_wood.pdf

I skimmed it a bit and oak is the most acidic (corrosive) species listed.

Some other googling shows wet oak+cast iron=bad news

Ianab

I'd say the wood is still wet. Oak logs would be almost impossible to dry in a kiln, well on any sensible commercial time scale anyway. The acidic tannins in oak are very corrosive, and will certainly react with iron.

Would be interesting to put a moisture meter on the boards, if they feel "wet", they probably are.

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

ladylake

 I agee, moister came from somewhere.  Either in the wood or if your shop is cold it could have been condensation on the saw.   Steve
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jcbrotz

I have found the term kiln dried to be used really loosely when they talk about logs for cabins. The logs are probably only down to 20 percent or so at best, I did some pine for a guy and his were around 25. You have some wet oak and now have a table saw to clean up :( :'(. I was kiln dried but the dont say how much.
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Tree Feller

Everyone is right.The tannin in the Oak combined with the moisture is what rusted your tablesaw so badly. That's one reason Oak is not favored for woodworking bench tops.

That first picture of the black marks on the board looks like it came from the infeed roller on your planer. Heavy, wet boards don't slide very easily and the roller can slip.

The stress you encountered while sawing is classic case hardening.  The outer shell of the log was dry and in tension while the wet core was in compression.
Cody

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WDH

Yep, metal turns wet oak black.  the good thing is that the discoloration is not deep and usually will plane out once the wood is dry.

Your "kiln" dry logs were still wet.
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Too Big To Fail

You can use that reaction as a stain if you like the purple-ish "blackened" look (I do).  You dissolve steel wool or old nails or whatnot in apple cider vinegar, let it sit for a day or so, and then apply.  Works best on red oak, but it will have some effect on other species as well, depending on the tannins in them I guess.

francismilker

I've seen that same reaction in the past when I helped out in a cabinet shop.  We once received a whole load of oak planks that were milled, air dryed (for a while), and then planed.  Every single board done as yours did and the equipment in the shop all corroded from working the wood. 

On the flip side, we made some of the most unique cabinet doors with the blue-streaked stuff I've ever seen. Even had folks come back and ask for more of them.  Problem was, it was the perfect storm that created those streaks and we ruined a bunch of good wood trying to duplicate it!
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terrifictimbersllc

Agree with the cause stated above, this is wet oak having contact with iron.  If it is worth the trouble, one can remove the black metal stain from oak by wetting the wood with a solution of oxalic acid in water.  Rinse off and repeat until the black color is gone.  The black is an iron complex of  tannic acid, formed from iron and the tannic acid in oak.  Sometimes called "wood bleach", oxalic acid chelates (complexes with) the iron, the resulting iron oxalate is colorless as opposed to the iron-tannic acid complex.   This is not really bleaching, which is an oxidation reaction.

p.s. this is why sawmills have stainless steel sleeves covering bed rails.
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logboy

Same as what everyone else is saying. Its a natural reaction.  I get the same effect on the bottom oak slab in the stack from the forks on the skid loader.  You might try putting a coating on your table saw and planer. I use Slip-It which is made by Grizzly.

http://www.amazon.com/Grizzly-G5562-Sil-Free-Sliding-Compound/dp/B0000E6TJ8/ref=cm_cr_pr_product_top
I like Lucas Mills and big wood.  www.logboy.com

Axe Handle Hound

In regards to your tablesaw top, scrub it down with some 0000 steel wool as soon as possible and you'll possibly find that there's very little, if any, lasting damage.  Any remaining stains in the steel can probably be buffed out by polishing with Bar Keepers Friend. 

Weezer

This gets much worse in oak (or most any other) wooden boats that used iron fastenings to hold the planks. Even galvanized will go after a while. It looks like the hole around the fastener is burned, all eaten out.  An iron sick boat is a BIG project, easier to fuel up the chain saw. :'( Don't know why anyone would use anything but brass/bronze fastenings, you just know it's gonna end bad, and soon.
                              Jim

GeneWengert-WoodDoc

The reaction of tannic acid, water and iron forms iron tannate.  This is a dark blue to black colored stain.  It usually will not go deeply into the wood unless the contact with iron is prolonged.  Note that the iron can come from a rusty pipe, vent, or even from water dripping off a roof.  I have seen iron tannate form in fairly dry wood and then it is a grey colored hue.  Wet wood formation is the most dramatic.  It can form on dry oak table top or floor if in contact with an iron pot, etc.

The cure is to use a weak solution of oxalic acid (about as strong as vinegar, so it is safe).  You can find it in a hardware store where it is used to remove iron stain from a sink, bath tub, etc.  It is also called wood bleach and would be with paints in the store.  It takes a few seconds for it to work.  Because we use so many metal items (sawblades, rollers, forks on a lift, etc.), it is virtually impossible to prevent metal contact.  Tannic acid is present in all woods, but especially oak.  Sometimes the oak seems much more susceptible to iron tannate stain than other times, perhaps because of variations in pH and maybe bacterial activity in the tree.

If oxalic acid does not work, then you have a fungal stain.  Fungal stains, including mildew, will be a series of small spots or even cotton-like.  Note that in the last picture posted, we see a bunch of small spots rather than the more continuous color in the other pictures.  Also note that the last picture seems to have a feathered edge where the color was wicked along the grain.  This last picture is either some paint or stain from the outside that was spilled on the piece or is mildew...it does not have the expected appearance of iron tannate stain.

OK?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

GeneWengert-WoodDoc

Prolonged contact with iron fasteners will actually weaken and destroy wood if moisture is present in the wood, resulting in a larger hole and poor fastener strength over time.  Stainless fasteners ($$) would be a top choice, or even aluminum, rather than  galvanized or untreated iron.  Sometimes fasteners coated with epoxy or similar polymers are used.  (Most RR ties, especially in medium to dry locations, are replaced because of this deterioration of the wood at the spike and at the tie plate and not because of rot or breakage.)  We also have similar deterioration of fasteners used in CCA treated wood; special fasteners should be used with this or similar type of treated wood.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Weezer

Gene, I remember being told not to use stainless in constant contact w/sea water, but don't remember why. I don't remember if it was a salt water issue or a wood issue. Do you? I'd rather use stainless, most types are harder than brass, making stripping or snapping the head of the screw off less likely.
                                                          Jim

redbeard

Learned a lesson long time ago using black iron bar clamps. I had just cut and threaded the pipes and made up several different lengths I was glueing some nice red oak boards together and after they dried and unclamped them they had the black stains I got them out by planning them but from then on I use wax paper as a protective barrier.
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hackberry jake

When I worked at a sawmill, I remember stacking oak lumber all day and if I ever touched metal after stacking lumber, My hands would stay black for a week.
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Magicman

Tannic acid contact is the reason that several portable sawmill manufacturers use the stainless steel covers on the bed rails.  If not all of the cants and many boards would have blue streaks across them.
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Ronnie

I never knew this could occur. Unbelievable!! The wood was wet coming off the mill because I was dumping the lube to it, but it was surface dry when I started planing it. So I guess my lack of experience got me in trouble. After a pass or two through the planer I noticed the wood was damp. I guess this is when I should have stopped. When is it safe ( at what moisture level ) to work with oak without having to worry about this tannic acid reaction? Should I do anything to clean my planer blade and rollers or do you think there ok? The logs where an extreme pain to cut with extremely off center pith and the constant movement, and now there all stained black and my table saw top is all boogered up. And now I need to clean these boards up with some oxalic acid. I am actually paying this guy to cut up his logs!! Education is expensive I guess. He thought these logs were dry and was planning on making a kitchen table out of this lumber for his new house. I guess he will have to wait until its dry. Would you guys clean his boards up with the oxalic acid before returning them to him?



 

Kiln dried log!
TK2000, JD5075, Stihl 660,270,170.

Ianab

You want it under about 20%. Then all the moisture is bound in the cells of the wood. Not "free" to cause trouble.

This is different from "dry" as in ready to build stuff. That needs to be more like 10%. The wood will shrink and move a bit while it looses that moisture, so you are better planing it after it's properly dry.

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Magicman

Quote from: Ronnie on October 10, 2012, 02:54:53 AM
some oak logs left over from his log home build. They are kiln dried logs

I have no idea how or how long it would take to satisfactorily kiln dry logs.  Obviously those were not.

Blue stain is also how you can detect metal in an Oak log before sawing.  I have seen a blue spot on a log butt many times and alerted the customer.  A decision was then made whether to jump butt it or even to discard it for firewood.  Blue stain can be your friend.
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

westyswoods

No expert here, although last year Beecraft and I milled some white oak threw it in the back of a flatbed with metal deck moved to a shed for stacking. Every piece which came in contact with the truck deck was stained badly.

Since I've had the same experience planning wet white oak shows exactly as your photos do.
Stay Safe and Be Healthy
Westy

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