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Help!! Why is my white oak table "bleeding"? And other questions??

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Forum topic by adamclyde posted 11-21-2016 04:33 PM 1096 views 0 times favorited 5 replies Add to Favorites Watch
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adamclyde

40 posts in 1751 days


11-21-2016 04:33 PM

So I’m finishing up a white oak table for the backyard. About 95% done so have it outside now doing the final touches. However, two questions.

First… it rained last night and I saw this this morning on the pavement underneath it. It completely stained my new concrete patio! this isn’t treated or stained… (pictures below). This is pure white oak… why on earth would this happen? The wood is directly on the concrete right now because I haven’t yet put in the metal leveling, which will raise it off the concrete a few millimeters, but even still… this is crazy for just a few hours of mild rain. But my big concern is… I thought white oak was an excellent outdoor wood. Why on earth would a little water do this? My wife is gonna be pretty mad when she sees this. Yikes. [side note… any idea how to clean this off of concrete. Looks pretty stained. Ugh.]

Second… finishing. I’ve read a lot on these forums for finishing for white oak… everything from painting to spar varnish. But I think I’d prefer the least maintenance and I’m good with it graying and weathering over time. However, for a little bit of protection does anyone use anything like Thompsons water sealer? I have exposed end grain on the legs, so is there something basic I can/should do to give it just a bit of protection against some water, or the inevitable red punch spill?

Thanks.


5 replies so far

View Mosquito's profile

Mosquito

9110 posts in 2130 days


#1 posted 11-21-2016 04:43 PM

Tannins in the wood are likely responsible for the staining. Same thing if you let leaves stay on it too long and if they get wet. I’ve not yet done anything about the staining we get from leaves on our driveway, but it seems like they mostly go away over time in our case. Washing and scrubbing or power washing would probably do it at this point I would imagine

-- Mos - Twin Cities, MN - http://www.youtube.com/MosquitoMods - http://www.TheModsquito.com

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mrbob

182 posts in 407 days


#2 posted 11-21-2016 04:45 PM

Thompson Water Seal is waxed based, if you use it, it will give finishing problems in the future if you want to use something else.

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JayT

5455 posts in 2049 days


#3 posted 11-21-2016 04:47 PM

White oak is an excellent outdoor wood due to its weather resistance and durability. The tannins in the oak, however, are water soluble and can/will leach out and probably what has stained the concrete. These are independent circumstances. The loss of tannins hasn’t affected the weather resistance of the wood, just the concrete.

I’m sure there are ways of removing the stain, but I don’t know them off the top of my head. I suspect pressure washing would take care of it, as it should dissolve the tannins that are now in the concrete and dissipate them, but don’t know for sure. Hopefully someone else can chime in there.

-- In matters of style, swim with the current; in matters of principle, stand like a rock. Thomas Jefferson

View adamclyde's profile

adamclyde

40 posts in 1751 days


#4 posted 11-21-2016 05:26 PM

Thanks guys. So with these tannins… will this continue to happen or will they stop leaching out? I can’t think of how to prevent this from happening every time it rains. I’m not sure I made the right choice of wood species! Yikes.

View Fred Hargis's profile

Fred Hargis

4758 posts in 2331 days


#5 posted 11-21-2016 06:04 PM

Let me suggest untinted exterior paint for the finish (more in a minute). A true marine spar varnish will also work, but will cost more and be a little more work. Avoid (read that again:AVOID) anything in the box store labeled “spar varnish”.....at least if you equate “spar” with “outdoors”. Now, to the paint: the deep color paint bases (the ones they use for tints) are usually numbered 1 through 4, generally the higher numbers are for the darker colors and without tint they dry clear, much like varnish (if it’s an oil based paint). Oil based paints are getting harder to find and many of the acrylic exterior paints (water borne) have the same properties, but they tend to dry very clear (no amber cast) even though they look milky in the can. But these paints (exterior, mind you) have the UV inhibitors and hold up very well outdoors. That said, any outdoor finish requires maintenance, but the paint and the true marine spar go a long time between recoating. (check here for more info on the pain) Lastly a word about the box store spar varnishes: most of them are urethane formulas, and urethane doesn’t do well in high UV. Flexner tested some of them for UV resistance and concluded that while the Min wax product is labeled that it has UV inhibitors, it did so poor in the tests he wondered if if really had any at all in it. I suspect if the post was finished that would stop some of the staining you see, presumably the finish would keep most of the water away from the wood preventing the dissolution of the tannins.

-- Our village hasn't lost it's idiot, he was elected to congress.

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