Black on milled oak that's been stored outside

[Randall J Cox]

I was given a lot of already milled oak, it's 3/4" thick. That's the good news. The bad news is that it was stored outside under a tarp for a couple of years with some of it stickered, and a lot of it turned black or have lots of black areas. I'm guessing it was due to water leakage. If I try to run these through my planer to clean off the black, then they will be less than 3/4". The black does not look like mold. Is the black "tannin" (I think that's the word) that has come out of the wood? Is there a chemical that might take off the black? Randy

[Jim Andrew]

Does sanding remove the black?

[Tom M King]

A pressure washer will get it right off. My pressure washer is 2500 psi at 4.4gpm. The gpm is not as important as the pressure. More than 2500 will erode the wood. I use a 40 degree nozzle, as one narrower than that will cut into the wood.

I have White Oak siding on our house, and barn, that I built in 1980. I pressure wash it about every 10 years or so. It turns a silver gray and that stays for 8 or 9 years. The black is probably mold, and mildew, but it comes right off.

I just use water. Bleach, and detergents can cause other problems, and I've found no difference in how long it stays clean.

This White Oak siding was pressure washed a day or so before I took this picture. It was starting to get black.

[Joe Wood]

If it's tannin stain, mildew or mold Oxiclean will get it off.

[Jacob Reverb]

White oak siding...is that even legal? Talk about sacrilege...I can't imagine being so flush with WO that I used if for siding...definitely a first-world problem! ;)

[Prashun Patel]

I agree that it is probably a reactive stain, not mold. You may be able to bleach this with deck cleaner. Sometimes it runs deeper. You can always ebonize it and go with the black.

[Randall J Cox]

I agree that it is probably a reactive stain, not mold. You may be able to bleach this with deck cleaner. Sometimes it runs deeper. You can always ebonize it and go with the black.

Ok, just did some googling for deck cleaner (thanks for idea!) and ended up reading about oxalic acid as that's seems to be the predominent ingredent in deck cleaner. I found many references to it cleaning off tannin stains (along with a long list of others). Think I'll buy a lb or two, mix with water and see how it works. At least I'm pointed in a direction now.... Randy PS Anybody out there used this for wood cleaning?

[Joe Wood]

Oxiclean does almost as good as oxalic with tannin stains, and it's a lot safer to use, might give that a try.

[Tom M King]

White oak siding...is that even legal? Talk about sacrilege...I can't imagine being so flush with WO that I used if for siding...definitely a first-world problem! ;)

I paid $100 a thousand for it when I built the house, and barn in 1980. That's 10 cents a board foot. On later spec houses I built here on the lake, I splurged, and bought dressed White Oak, which wasn't much more. Soon after I built the house that siding is on, Senco had stainless nails available here, so no more of that problem.

As I have built additions onto our house, I've pulled off that top layer, to use as the first layer of Board on Board, so the streaks are no longer seen. That picture is the last section of our house with the original outer layer on it, but that will be used for the next addition.

This is timber country, and there are multiple mills that sell lumber from what grows around here.

Seriously, I've dealt with this black stuff on White Oak for 40 years now, and it comes right off with water pressure. If you put a chemical on it, you're still going to have to rinse it off. This is first hand experience, and not just conjecture.

[Jacob Reverb]

I paid $100 a thousand for it when I built the house, and barn in 1980. That's 10 cents a board foot.

I'd say that qualifies for a belated YOU SUCK! award!

Seriously, nice score. I've bought green white oak from sawmills around here (usually 60¢/BF), but we get these weird tunnels through it (insects? rot? dunno) that are coated with something black, probably the same stuff as on the OP's wood. I asked the sawmill operator about it, and he said, "The further south you go, the poorer the hardwoods get and the better the softwoods get...and vice-versa."

[Matt Day]

Jacob, I guess you missed the whole drama about the “you $uck” phrase. It’s not permitted here, though I know you said it as a compliment.

[Tom M King]

I know the story, and don't mind a bit. I bought it by the semi load, and used it on several houses over several years. The clear, big logs are sold for high dollars as veneer logs, but the rest is just cut up however you want it with no grading.

The first two houses I built here on the lake had Cedar siding on them. Flying squirrels ended up in both attics. Woodpeckers like it too. They can't do anything with the White Oak. Some of those houses, that I sold back then, have been resold for over a million back when things were crazy.

The last White Oak I bought, a few years ago for an addition, was .65 a foot for dressed. Green works fine for this vertical, board on board siding.

We're right where the Coastal Plain starts to turn into Piedmont, and hardwoods are just fine, as are what softwoods grow here. The counties around us are the largest producers of timber in Virginia, and North Carolina. We're right at the border of both. The lake is mostly lined with houses now, but for many miles in all directions behind those, it's mostly all timber land.

[Randall J Cox]

Oxiclean does almost as good as oxalic with tannin stains, and it's a lot safer to use, might give that a try.

Joe - As my wife (nor I) have any experience with Oxiclean, is it a liquid or powder, how did you use it? The oxalic acid is a powder you mix and have to keep hot and then triple rinse to get it all off. Just wondering about all the water going on to one of these boards...maybe as it probably wouldn't have enough time to penetrate, might not make them cup/warp/etc. That was also my concern about pressure washing - driving the water into the board. I'd rather try oxiclean first, less hazardous. And, don't own a pressure washer. Randy

[Joe Wood]

It's a crystal Randall, mix in hot water, spray or brush it on, use a brush to scrub for a couple minutes and rinse it off.

[Dave VanDewerker]

If this is white oak, it is just the tannin stain, no amount of sanding will remove it. I have some air dried white oak that is as dark as walnut and is solid color all the way thru.

[Tom M King]

The pressure washer cleans it so fast, that I doubt the wood absorbs any more water, to amount to anything, than coating it with some chemical, and then having to rinse it off. No worries about anything getting left behind to play with finishing later.

It's going to have to be dried some after either process in a low humidity environment anyway. One pass with the pressure washer blasts it right off, down to bare, clean, new looking wood, as in my picture.

It's not tannin stain. I have done the same with some that I had stored under a tarp too, and it looked like it just came from the mill, as does the siding that's had this treatment for at least four times in 40 years.

My pressure washer came from a rental place that was going out of business. They are a fairly common rental item, but I have no idea what they rent for. I bought mine 25 years ago.

[Randall J Cox]

The pressure washer cleans it so fast, that I doubt the wood absorbs any more water, to amount to anything, than coating it with some chemical, and then having to rinse it off. No worries about anything getting left behind to play with finishing later.

It's going to have to be dried some after either process in a low humidity environment anyway. One pass with the pressure washer blasts it right off, down to bare, clean, new looking wood, as in my picture.

It's not tannin stain. I have done the same with some that I had stored under a tarp too, and it looked like it just came from the mill, as does the siding that's had this treatment for at least four times in 40 years.

My pressure washer came from a rental place that was going out of business. They are a fairly common rental item, but I have no idea what they rent for. I bought mine 25 years ago.

i
I'll look into the rental of a pressure washer, sounds much easier than trying to do it by hand. And I have so much of it.... Thanks.

[Randall J Cox]

If this is white oak, it is just the tannin stain, no amount of sanding will remove it. I have some air dried white oak that is as dark as walnut and is solid color all the way thru.

This is not white oak, just the regular stuff we get here on the west coast. Randy

[Tom M King]

If you like, send me an email when you find out exactly what type pressure washer you can rent, and what nozzles come with it. May is always pressure washing month for us. We do museum houses too that no damage can be done to. I've done a lot of it, and might be able to save you some learning errors.
historichousepreservation@gmail.com

or post it here, and someone else might get some benefit.

edited to add: Every Oak in the U.S. is either a White Oak, or a Red Oak. That doesn't mean that any are White Oak, or Red Oak, but I expect they will all react very similarly to power washing.

[Randall J Cox]

Well I borrowed a 2500 PSI pressure washer, used it and unfortunately that didn't phase the black stuff. So next I scrubbed with oxiclean and let it sit on the boards for 15-20 minutes like the can said, then pressured washed it off - black still there but it did lighten them somewhat but not to the extent of making the boards usable without planing. As they are all already 3/4".... The only thing left to try is oxalic acid. This is turning out to be a lost cause. Randy

[Tom M King]

Sounds like it's a lot tougher stuff than what we deal with here, or maybe just the difference in the type of Oak.

[Thomas L Carpenter]

I have a white oak table top that lives outdoors under cover that has black stains on the edges and a little on the top. Coated it with spar varnish a few years ago knowing i would have to refinish it every few years. The finish is still looking great but the black stains are ugly. Pressure washer didn't touch it so I assume its under the finish. Guess it'll have to wait until it's time to strip and refinish.

[Randall J Cox]

I made two white oak patio tables two years ago (boy is that stuff expensive and heavy). No finish or oil at all. I kept mine covered in winter (new cover, no water leaks) and still looks great. The other I gave to my daughter across town, no cover over winter, hers looks terrible.

I think with all the rest of the milled oak I have, I'll buy a Wixey gauge (any other recommendations?) and mount on my planer and just plane most or some of the black out. I will need to keep the boards for a project all the same thickness, obviously somewhat less than 3/4" where they are now... Think I have ruled out using oxalic acid, too much work and scrubbing and rinsing for something like 70 boards, some both sides. I would probably be more affected from the acid than the boards would. Plus its a lot of work.... Woodworking lessons learned I guess. I do appreciate the comments and recommendations - great forum! Randy

[Bill Brady]

In my younger years I worked in a sawmill. We sawed a lot of Oak, it would stain where the stickers touched if it didn't get in the kiln quick enough. If it was left in round packs before it was put on sticks it would stain sometimes. Sometimes the stain was deep and the board grade was affected.

[Tom M King]

I guess the difference in Randall's, and my siding is that the siding is exposed to the air, whereas his was wrapped. The black that gets on my siding is probably just mildew, and dirt on the surface.

[Randall J Cox]

I bought some oxalic acid and mixed per instructions, did wonders on the black stuff on the white oak table. I hosed it off, let it dry and its now not black but light gray and even. I'm going to give it another oxalic acid bath in the morning with some clean fresh stuff to see if I can get more of the gray stuff off. The first bucket full of solution was getting nasty black and was just smearing around the black goo on the table top that the acid was loosening. I'm also going to try it on one of the non-white oak boards I was given with all the black stuff. By the way, I did buy and install a Wixey gauge for my planer so I can plane off the black stuff. Tried it on a board or two and it cut the surface black off down to nice clean oak with only one light pass. The black was just on the surface. Randy

[Randall J Cox]

Ok, final analysis... The oxalic acid did wonders for the white oak table that has been outside for two winters. I tried it on some of the non white oak boards (just regular oak) that I was given, didn't touch the black stuff for some reason. Scrubbed both with scrub brush and applied the solution at least three times. Why such different results I don't know. Randy