Black on milled oak that's been stored outside

[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