Our red oak windowsills that are about 16 years old are in need of a refinish. The wood is black in some parts which maybe due to the moisture from the windows. Do I sand the wood until the black disappears or is there a solvent available that will clean the wood? Is there any risk in me sanding too much to remove the black? I am assuming that the black is just surface deep. After I remove the black, I was going to add coats of clear polyurethane.
Does anyone have any other suggestions on how to make this windowsills look beautiful again? Thanks. Regards, Sandy
Red oak develops black patches and streaks wherever iron and moisture come in contact with it. The discoloration is probably deep into the wood. If you try to sand the spots where the wood is discolored, without sanding the entire surface evenly, you will definately see divots where you sanded heavily, magnified by the clear poly.
Oxalic Acid wood bleach is the recommended stuff to scrub in to remove most of the discoloration. Then try a medium brown oil stain such as Minwax Special Walnut, or Sherwin Williams equivalent, and finish with a satin polyurathane varnish. This will hide the current discoloration and the discoloration that will undoubtably continue to occur, as much as possible.
I've done quite a bit of this, and my best results came from the following-
First off, sanding is a rediculous amount of work- the old finish will gum up the paper, and it will take forever. What you want to use is a cabinet scraper (which is a flat rectangular piece of steel that you will likely need to mail-order from a place like Lee Valley- most hardware stores no longer carry them) for the flat pieces, and a curved contour scraper for the detailed areas- those usually look like a teardrop mounted on a handle.
Scrape off as much of the finish as you can- that *should* be down to the bare wood, using even strokes. Pay attention to the grain of the wood- it will cut better one way than the other. If what you're doing seems to leave a rough surface, then scrape in the other direction. If you don't want to buy a cabinet scraper, an ordinary wood chisel will work in a pinch- remember that in this case, you are not chiseling with it- you are dragging it along the wood with the edge facing down. Sharpen often.
Once the scraping is done, vacuum off the sawdust and give it a quick wipe with water to raise the grain. *Then* sand it- if your scraping left a decent finish, 220 grit should be fine.
If you still have black marks, get some wood bleach (*not* household cleaning bleach) and follow the directions on the container. You may have to repeat several times to lighten the dark areas.
Neutralize the bleach according to the instructions, give it final sanding, and then apply your stain. (Sherwin Williams "Fruitwood" looks superb on red oak) After the stain is fully cured, apply your top coat (usually Polyurethane).
You will probably want stain- even if you bleach a lot, there will still be some of that black left in the wood. I suggest the fruitwood because it darkens the grain, and blends that discoloration in really well, along with having an excellent red color to it.
I would avoid at all costs using a heat gun *or* chemical strippers. Believe me, I've tried them all- and they just do not work as well as simple scraping on old finishes.
The down side is that it's not really called for. Oak stains so nicely, there's no reason for a gel stain. Almost any old stain will do the job without blotching, but some don't look good because they're the wrong color. (That's all in the eye of the beholder, of course.)
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