Black stain on exterior oak door


I have a wooden exterior door on my house (oak). I stained the door and then put an exterior polyurethane sealant on it (5 coats). Moisture must have gotten under the sealant because some black stains have appeared under the sealant, to the point where it must be redone.
I'm in the process of stripping the polyurethane and that's going pretty well.
My questions are:
Once the sealant is off, does the door have to be sanded down to the bare wood (remove all the natural oak stain that I originally applied?
How to remove the black stains?
What to reseal it with?
Any suggestions?
Stephen
P.S. We are in Florida, near the ocean (not the greatest location for a wood door, but several neighbors have them, and they've been able to have a wood door, as long as it was well sealed?
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snipped-for-privacy@rogers.com wrote:

Red oak or white? Red Oak is porous and prone to rot and mildew.
There are at least wo kinds of wood bleach on the market. One is oxalic acid, the other is a two-part bleach using sodium hydroxied and hydrogen peroxide. I've tried both on red oak. The oxalic acid didn't seem to do anything, the two-part bleach worked OK.
Shellac is reputed to be the best base coat to use as a moisture barrier so that may be your best bet after you are down to bare wood. For the best results it should be mixed fresh from flakes, see http;//www.shellac.net. For second best results using pre-mixed shellac check the date on the bottom of the can and use the freshest you can find. If you use the 3 lb shellac from the can thin it about 2:1 shellac to alcohol. Use dewaxed shellac.
Then you can go over the shellaced door with a good exterior varnish.
Good luck.
--

FF


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snipped-for-privacy@spamcop.net wrote:

White oak.

So you're saying that it would be better to go with a bleaching product made specifically for wood.
My guess is that I'd have to apply it to the whole door, otherwise the part where the stain was bleached would appear a different color, no?

When you say down to bare wood, do you mean sanding off the stain, as well. I've been able to get the polyurethane off using a poly remover,and scraping it down. The wood still has the color that I stained onto it when I began. I can only think that to get that color off, I have to totally sand down the entire door. Is that necessary? I just want to know. I will do what is required.

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snipped-for-privacy@rogers.com wrote:

Good.
Yes. I'd only turn to chlorine bleach as a last resort.

Maybe. I'd try it just on the black stains first and see what happens. Even if the bleach does fade the color, you may be able to recolor it with more stain. If the door is not too old it may match. Staining wood twice supposedly does not change the color as the wood picks up as much stain as possible on the first application.
But I can't ses your door. Problems near the bottom of the door won't stand out like they would at eye level.

No. A true stain doesn't really seal the wood.
--

FF


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snipped-for-privacy@rogers.com wrote:

No, and it would be impossible w/ porous oak anyway unless you take off an inordinate amount of material

Oxalic acid (deck cleaner)...

Good quality exterior spar varnish...
Don't say where the staining occurred so can't do more than conjecture on cause. Couple of possibilities are points of penetration of hardware, a brittle former topcoat that fractured, a scratch that broke the surface, a path under the topcoat around a door panel, ...
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OK. thanks.

I would apply it to the stains only, or the entire outside face.

The stains were mostly on the lower half of the exterior, across the entire bottom of the door, and near where a kickplate would go. The door is covered by a portico so the top part is sheltered.
It did get a lot of exposure during the hurricanes last fall, so seawater/rain/wind probably played a good part in all of it. (We would have covered the door, but we weren't here.
Thanks for the tips.
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snipped-for-privacy@rogers.com wrote: ...

Try it...probably will want to do the whole door to even it out. If is effective against the particular stain (and I suspect it will be), it will probably be fairly easy to get a reasonably good match.
...

Probably a good plan/decision... :)
I'd say if it wasn't stained significantly prior to that time your surmise is correct--the strong wind essentially did an accelerated aging test.
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Just wanted to say thanks to all who posted their responses. The oxalic acid worked great and the door came back better than I thought it would. I applied it to the entire door. It did lighten the color somewhat, plus the sun bleached it over the past year, so I do plan on restaining it before resealing.
Thanks again.
Stephen

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snipped-for-privacy@rogers.com writes:
[...]

Beware of darkening the door to much, because a dark door will get hotter from sunshine than a light coloured one, thus aggravating any aging effects.
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto: snipped-for-privacy@physik.uni-bonn.de Phone: +49 228 73 2447 FAX ... 7869
  Click to see the full signature.
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If the black stains are oxidation from metal, which can be dust from the grinder, to nails, lemon juice works well. Apply to the stain, and let it sit, sometimes you have to leave it on overnight, and/or do multiple applications. robo hippy
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snipped-for-privacy@rogers.com wrote:

Got any iron/steel in the door? Fastenings, whatever... If so, remove and replace with bronze best) or brass else the door will stain again.
-- dadiOH ____________________________
dadiOH's dandies v3.06... ...a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico
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