Dirty Stain On Hardwood Floor Requires Klean-Strip


I am working on a house built in 1951. It has oak floors with the original finish, waxed, have been covered with a wall to wall rug for their lifetime. When we were prepping the walls and ceilings with TSP, some drips got past a drop cloth that got shifted. There was a lot of soot on the ceiling, so the tsp water was very dirty. It left very dark spots that went through the finish. (I sanded down a small area to find out if the spots were in the finish or down into the wood, and it was definitely into the wood.) Should I try to strip that section of the floor, masking it off? What bleach product should I use? How do I use bleach? What should I use to strip it? What should I put on the floor afterward? The floors are in such nice condition that I’m not going to refinish the rest of the house, just wax. Is it possible that the floor is not varnished, but only stained and waxed? What were they doing for finish in the 50’s?



Dear Delia

It sounds like what ever finish is on the floor, it is not very sound. Meaning that the finish film is not thick enough to hold back water. And TSP mixed with soot has really done it’s work. I’m not sure of the chemistry involved, but I hope this is just a simple case of water staining. Standing water will always turn wood black, but I’m sure the soot didn’t help. I’m not sure what a weak alkaline solution like TSP would do, but I think that it’s affects would be negligible.

So, if you are sure that the stains are in the wood itself, I’m going to describe how to bleach out various stains. I’m really betting this stain can be bleached with the simple oxalic acid. It’s easy to use and fairly safe in the liquid form. I doubt the chlorine will work but I’ll mention it here anyway. And the last resort is Klean-Strip. Here goes.

There are three different kinds of wood bleach and they each act on different stains. For all these bleaches you will need to remove all the finish from the wood surface, either by sanding or chemical stripping. You can read about chemically stripping wood floors also in this web site.

While you are sanding the finish off, this will give you a chance to see how deep the stain is. If you are really lucky you can sand enough wood off so that most if not all of the stain out. Use 80 grit sandpaper, and finish with 100-120 grit. I will usually use a wood scraper for the initial removal, but will always finish up with hand sanding anyway. But you will have to learn how to sharpen a scraper to razor fineness before you use it on your smooth floor. That s another subject for another time. Use sandpaper if you cannot sharpen a wood scraper well. Hand sanding just takes a little more time, but does the same job.

The first wood bleach is oxalic acid, in liquid or crystal form. This will remove most water and iron rust stains. Apply a strong solution and wait several hours or overnight if needed. Wash off wood surface with lots of water, with a bit of baking soda to neutralize the acid. A lot of deck brighteners have oxalic acid in them. But I like to buy my oxalic acid in it s pure crystal form, at hardware stores or even a pharmacy. In this dry form, it s highly toxic, that s why it s getting harder to obtain these days. Make sure you don t inhale any of the dry dusty residue on the floor. That s why you have to wash it off quite well, before you fine sand that spot again.

The next bleach to try is a chlorine bleach. This will remove most dye stains, caused by grape juice, blood or coffee and tea spills. The weakest form of this bleach is regular laundry bleach. It’s worth a try , but it may be ineffective. Better to use swimming pool bleach, called Shock Treatment (dry calcium or sodium hypochlorite). Mix the crystals with hot water, until solution is saturated. Apply to the spot and it should work right away, but try twice if needed and wait overnight. Neutralize the bleached area with vinegar, so it doesn t ooze chlorine droplets after the wood is finished. Wash it all off with lots of distilled water and let the wood again dry overnight, before refinishing, if it did work. Sometimes even this bleach will take too much color out of the wood, and you will need to replace some of the wood s tone with a light wood stain, before you replace the finish.

And lastly for organic stains, like urine and feces, your only hope is to use hydrogen peroxide and sodium hydroxide, in a very strong and dangerous concentration ( 27% ). Klean-Srtip is one of these products that s readily available in North America, and comes with good instructions. Visit their web site at www.kleanstrip.com for info on how to use this stuff. You generally have to mix the two parts of these bleaches together, but this contains it own neutralizer, so only a washing up with water may be needed after. Click on the product button at the Klean-Strip site, then the wood bleach link. This last type of bleach will always turn the dark spots to an off white color, which you will then have to blend in with a light colored wood stain to match the color of your finished wood floor.

All these bleaches are water based, so they will raise the grain and make the wood rough. Be sure to let the wet wood dry overnight. And do be careful when you sand it smooth the next day, so as not to sand out the bleached effect. Do the final sanding with just a little pressure and use 120 grit sandpaper, just until the wood is smooth. Or go over the whole floor gently with a 100 grit screen on a floor buffer, keeping the handle low, to ease the pressure.

Just remember bleaching doesn t remove the stain, it just changes it color. You will, in most cases have to re-color the wood with a wood stain, before you apply a floor finish. You will find that the small cans of Minwax stains most convenient, but you might also try the touch up stain pens they sell in the stores. These contain a dye stain, which is a lot easier to blend in. The pens, although expensive, allow you to paint in bleached out grain lines as well as the background color. Start with the lightest background color first then paint in the darker grain lines. Rarely can you just splash on a stain and expect it to blend well.

Also seeing how the surrounding old finish itself has aged you might try adding a pigment to the matching finish. Minwax stains are dye-pigment combos so they might work if added to the finish, but may alter the dry time The dry powdered earth pigments though will give you the instant finish aging you want. Pure earth pigments can be ordered from Lee Valley Tools and I’ll give you the URL for the pigments and the touch-up pens, if only just to see a picture of the products I refer to.



So now your next question is how to restore the floor finish without sanding down the whole floor. I’m going to send you the link to the second half of my famous floor maintenance article. Read the whole thing, it’s a complex subject, you have to do the chemical tests I describe to really determine what the floor finish is. It also describes a bit of finish history.