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Oxalic removed stains returning

11/15/17       
Ed Arthur Member

Website: http://doorsbyinvision.com

Are used oxalic acid on some interior trim on a 1959 morris minor traveler. I found that after removing the oxidized areas not only in the grain but around old screws etc. after a few months they came back. This has happened to me before on other projects. In this case I top coated with oil based polyurethane. I have all wood to do on the outside and it’s way worse but I don’t want it coming back after putting a lot of work into cleaning it up. I even sealed all sides of those trim pieces but it was maddening to see it create back. Any thoughts?
Ed Arthur

11/15/17       #2: Oxalic removed stains returning ...
Robert Member

Old car, you most likely removed the superficial staining but those stains run deep into the wood. How much sanding did you do prior to the Oxalic Acid treatment and what grit did you use ?

What a great project !! Best of success.

11/15/17       #3: Oxalic removed stains returning ...
Bob Niemeyer  Member

Website: niemeyerrestoration.com

Ed, what was your process last time? also how strong was your mix with the acid? On car wood did you back seal? Did you check moisture content on wood before finishing?

11/15/17       #4: Oxalic removed stains returning ...
Ed Arthur Member

As my post said, yes I did see you all sides. Typical sanding process starting with 120 to 180. I’m not sure what my solution was probably a little less than saturation point.
I know the stains on the exterior will go way deeper into the word because it’s Ash. If I were smart I would just replace the wood but I’m not.

11/15/17       #5: Oxalic removed stains returning ...
Bob Niemeyer  Member

Website: niemeyerrestoration.com

It is weird they came back. I have never in my 37 years of doing this have that happen.
There must have been enough moisture left to keep the oxidation process going.? I would use a finish that will "lock up" the wood better. I would use a Exterior 2k urethane system with a Isolante on the bare wood first. Lots of good systems out there.

11/16/17       #6: Oxalic removed stains returning ...
Ed Arthur Member

Hi Bob. Yeah, I just wanted to go old-school with the interior. On the outside I’m going to use my profane 4800 2K polyurethane made by pro line which is sure when Williams. It’s what I use on all my exterior front doors that I’m doing now. It just makes me nervous to think that if I do all this work to clean up this wood on the outside that it might come back to haunt me! I don’t need that. Years ago I stripped an entire home full of cabinets and beams that were distressed red oak stained brown and I bleached and used oxalic acid on everything and then white washed it. About a year later I saw the job and the whole thing had turned gray! I think with all the stripping and washing the wood wasn’t totally dry.

11/16/17       #7: Oxalic removed stains returning ...
Robert Member

Its advantageous to apply the Oxalic Acid solution in the sunlight if at all possible. Add to that that it also works quite well if its mixed in very hot/almost boiling water.

Once the solution had crystallized, did you use any neutralizer products other than water to rinse it off ?

Since your dealing with a solid chunk of wood, I would try a much coarser grit of sand paper. Those stains are pretty deep into the wood so a coarser grit could help remove them prior to re-bleaching.

11/16/17       #8: Oxalic removed stains returning ...
Ed Arthur Member

Is there a better neutralizer?

11/16/17       #9: Oxalic removed stains returning ...
Bob Niemeyer  Member

Website: niemeyerrestoration.com

Yes the acid always works better when hot and wood is warm. A little sunlight does seem to help. To neutralize I like to overkill it.
First I do a clear water rinse, then a vinager/water mix rinse with a clear water re-rinse, then a sodium bicarb rinse with a clear water rinse to follow. This is all done back to back so the piece isn't soaking wet very long. I use a 25/75 mix of vinager/water 25% on the vinager. The sodium bicarb is a 3% solution. May be over kill ,but it has never failed me.

11/17/17       #10: Oxalic removed stains returning ...
Robert Member

After removing the crystals via real warm water and a Maroon Scotch-Brite Pad,once the surface has dried , I follow it up with a good rinse using a Maroon Scotch-Brite pad and Alcohol.

11/17/17       #11: Oxalic removed stains returning ...
Ed Arthur Member

Website: http://dorsbyinvision.com

I’ll do that. Thanks for the advice.

11/18/17       #12: Oxalic removed stains returning ...
dean c

Website: http://www.refinishny.com

you may also consider locking it down with shellac as a barrier coat.


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