Dining room floor is red oak with polyurethane finish. A plastic bag
with some dishes sat in one place for a couple of weeks - when I
removed it there was a dark blue/green/black stain.

The stain is in the wood. Tried scraping, but it apparently goes
deeper than I'd prefer to scrape. Used a hot oxalic acid solution on
it a couple of times, but doesn't make much difference. I tried it
after the wood was scraped, so it very definitely penetrated.

It looks like an iron stain, but the oxalic acid usually bleaches
those very well. All I can think of is that maybe one of the dogs
urinated on the bag while it was sitting there, but that's just a
guess.

Has anyone found that the two-part bleaches, or anything else, work
when oxalic acid won't?

John Martin

"John Martin" wrote in message
...
Dining room floor is red oak with polyurethane finish. A plastic bag
with some dishes sat in one place for a couple of weeks - when I
removed it there was a dark blue/green/black stain.

The stain is in the wood. Tried scraping, but it apparently goes
deeper than I'd prefer to scrape. Used a hot oxalic acid solution on
it a couple of times, but doesn't make much difference. I tried it
after the wood was scraped, so it very definitely penetrated.

It looks like an iron stain, but the oxalic acid usually bleaches
those very well. All I can think of is that maybe one of the dogs
urinated on the bag while it was sitting there, but that's just a
guess.

Has anyone found that the two-part bleaches, or anything else, work
when oxalic acid won't?

John Martin

Hello,

I would take another shot at Oxalic Acid. It sounds as though you are
going to have to strip the finish off of the stain before going at it again.
Make sure the Oxalic Acid solution is saturated and let it sit until dry.
You will have to wipe up the resulting dried crystals with a damp cloth. Do
NOT brush it up. It will have you sneezing your brains out if you sweep it.
Also, do not let the dog anywhere near the spot when it is being treated.
Oxalic Acid is quite toxic.

If you can manage it, try to have sunlight hit the spot while it is
being treated with Oxalic Acid. The sunlight will help bleach the stain.

I would try hypochlorite bleach if the second treatment with Oxalic Acid
did not work. I have used swimming pool hypochlorite instead of "Clorox"
since you can make it up to be a stronger solution.
I would move onto the two-part wood bleach, caustic and Hydrogen
Peroxide, as a last resort.
Once you get the stain out, I bet you will have to recolor the area and
then spot finish it. This will not be fun.

Good Luck.

On Feb 3, 3:39*pm, "Baron" wrote:
"John Martin" wrote in message

...





Dining room floor is red oak with polyurethane finish. *A plastic bag
with some dishes sat in one place for a couple of weeks - when I
removed it there was a dark blue/green/black stain.

The stain is in the wood. *Tried scraping, but it apparently goes
deeper than I'd prefer to scrape. *Used a hot oxalic acid solution on
it a couple of times, but doesn't make much difference. *I tried it
after the wood was scraped, so it very definitely penetrated.

It looks like an iron stain, but the oxalic acid usually bleaches
those very well. *All I can think of is that maybe one of the dogs
urinated on the bag while it was sitting there, but that's just a
guess.

Has anyone found that the two-part bleaches, or anything else, work
when oxalic acid won't?

John Martin

Hello,

* * I would take another shot at Oxalic Acid. *It sounds as though you are
going to have to strip the finish off of the stain before going at it again.
Make sure the Oxalic Acid solution is saturated and let it sit until dry.
You will have to wipe up the resulting dried crystals with a damp cloth. *Do
NOT brush it up. *It will have you sneezing your brains out if you sweep it.
Also, do not let the dog anywhere near the spot when it is being treated.
Oxalic Acid is quite toxic.

* * If you can manage it, try to have sunlight hit the spot while it is
being treated with Oxalic Acid. *The sunlight will help bleach the stain.

On Feb 4, 11:11*am, John Martin wrote:

I scraped down through the finish before using the oxalic acid the
first time. *Have used it probably three times, and each time it was a
hot solution as saturated as it would get.

That may be a problem; oxalic acid is unstable, it wants to
stay cold (and of course, you have to handle it with
glass or plastic, it gets poisoned in a steel or stainless
container).

It makes iron stains go away by dissolving the iron, but you
want to rinse away the solution or the iron comes back
again when the oxalate destabilizes.

Rather than scraping, I'd use a chemical stripper.
It's much easier, and finish penetration might defeat scraping.

"whit3rd" wrote in message
...
On Feb 4, 11:11 am, John Martin wrote:

I scraped down through the finish before using the oxalic acid the
first time. Have used it probably three times, and each time it was a
hot solution as saturated as it would get.

That may be a problem; oxalic acid is unstable, it wants to
stay cold (and of course, you have to handle it with
glass or plastic, it gets poisoned in a steel or stainless
container).

It makes iron stains go away by dissolving the iron, but you
want to rinse away the solution or the iron comes back
again when the oxalate destabilizes.

Rather than scraping, I'd use a chemical stripper.
It's much easier, and finish penetration might defeat scraping.

Hello,

Oxalic acid is not really unstable. It has a melting point just above
the boiling point of Water so hot Water should not be a problem. A solution
kept at ambient temperature works just fine after several years.

I assume you mean that a hot solution "wants" to cool to ambient
temperature. A hot solution will hold more of the acid than a cold
solution. As the hot solution cools, the acid will crystallize. I have
never found that to be a problem other than it leads to more dry crystals to
wipe up after the iron has been chelated and the stain removed.

Hi John,

Were you successful in removing the stain? If so, could you post how
you removed it? Thanks.



Andy Tenka



On Jan 31, 10:52*pm, John Martin wrote:
Dining room floor is red oak with polyurethane finish. *A plastic bag
with some dishes sat in one place for a couple of weeks - when I
removed it there was a dark blue/green/black stain.

The stain is in the wood. *Tried scraping, but it apparently goes
deeper than I'd prefer to scrape. *Used a hot oxalic acid solution on
it a couple of times, but doesn't make much difference. *I tried it
after the wood was scraped, so it very definitely penetrated.

It looks like an iron stain, but the oxalic acid usually bleaches
those very well. *All I can think of is that maybe one of the dogs
urinated on the bag while it was sitting there, but that's just a
guess.

Has anyone found that the two-part bleaches, or anything else, work
when oxalic acid won't?

John Martin

On Feb 15, 1:09*pm, wrote:
Hi John,

Were you successful in removing the stain? *If so, could you post how
you removed it? *Thanks.

Andy Tenka

On Jan 31, 10:52*pm, John Martin wrote:



Dining room floor is red oak with polyurethane finish. *A plastic bag
with some dishes sat in one place for a couple of weeks - when I
removed it there was a dark blue/green/black stain.

The stain is in the wood. *Tried scraping, but it apparently goes
deeper than I'd prefer to scrape. *Used a hot oxalic acid solution on
it a couple of times, but doesn't make much difference. *I tried it
after the wood was scraped, so it very definitely penetrated.

It looks like an iron stain, but the oxalic acid usually bleaches
those very well. *All I can think of is that maybe one of the dogs
urinated on the bag while it was sitting there, but that's just a
guess.

Has anyone found that the two-part bleaches, or anything else, work
when oxalic acid won't?

John Martin- Hide quoted text -

No success yet.

First try was the oxalic acid. Hot, saturated solution. Scraped
through the finish and well into the wood, and flooded on the oxalic
acid solution several times. Some small improvement, but it may have
been due more to the scraping and some dissolving of the stain than
any chemical action. I've used oxalic acid many times before and know
that it usually works quite well.

Second try was with some 12% sodium hypochlorite (pool shocking
solution). This is about twice as strong as regular laundry bleach.
It may have lightened the stain very slightly, as with the oxalic
acid, but if it did it was probably due more to dissolving the stain
than to chemical action.

I may try the opposite tack next - a reducing agent such as sodium
hyposulfite. Maybe lye or hydrochloric acid. Or maybe a two-part
wood bleach. Something has to work, and I really don't want to scrape
any deeper than I already have.

I'll post results when I have trhem.

John Martin