Replies

1. 
   mrbird90 | Jun 13, 2009 11:26pm | #1

   My daughter has the same problem with some white oak chairs that are painted white. I believe the black spots are some type of mold and the only thing that will remove them is 1 part bleach to 3 parts water with a little dish detergent added to act as a wetting agent. The chairs are kept on a covered front porch but are exposed to some rain and late afternoon sun . We tried power washing but unless you were very careful the paint started to peal off

1. 
   NietzschesMustache | Jun 13, 2009 11:57pm | #2

   Thanks, but the solution I used was stronger than 1+3, with no result.

2. 
   sapwood | Jun 14, 2009 12:03am | #3

   Any type of iron filing can cause tiny black spots. If you used steel wool on the oak, that could likely be the culprit.

3. 
   HowardAcheson | Jun 14, 2009 01:30am | #4

   Watco Teak Oil is heavy with linseed oil. Linseed oil is like candy to mildew. It's really not a good choice for outdoor furniture unless you frequently wash the furniture. To be effective, teak oil needs to be re-coated every couple of months

   At this point, you first need to kill the mildew. A 50/50 solution of fresh Clorox and distilled water will do that. Then to get rid of the black, use an oxalic acid bleach. You can get it at many paint stores. Follow the directions on the package.

   Finally, sand the surface.

   Howie.........
4. 
   boilerbay | Jun 14, 2009 03:23am | #5

   I agree with Howard. Clorox. In the south and out here where I'm at now (the central Oregon coast) one of the causes that I've seen is from the pine pollen. Comes down mustard/green but mildews out to black. After treatment, keep rinsed off and rotate in sun. A yearly thing.

   Boiler

1. 
   NietzschesMustache | Jun 14, 2009 03:44am | #6

   I tried chlorine bleach a couple of times, and it made no difference, so they must be iron stains. I'll try oxalic acid tomorrow.

   The FPL on iron stains

   I didn't use steel wool on them, so any iron must have blown in on the wind. The porch is about twelve feet from the street. Mucho thankos to everyone who answered.

5. 
   doorboy | Jun 15, 2009 05:45pm | #7

   As stated before, oxalic acid should remove the 'bluestain' spots. I'd then re-sand them and avoid a lacquer finish. Iron certainly DOES cause bluestain--which is a reaction to iron and the tannic acid in oak.
   It sounds crazy, but the iron can be transferred to the chairs through perspiration as well as being airborne.
1. 
   davcefai | Jun 15, 2009 10:13pm | #8

   The bleach will kill the mould but the corpse then needs to be removed :-)Have you tried scrubbng with a stiff nailbrush?

1. 
   NietzschesMustache | Jun 16, 2009 01:02am | #9

   A stiff brush, yes, but to no effect. No one local carries oxalic acid so I had to order some. Be here Friday. I tried scrubbing with Barkeeper's Friend which has some oxalic acid in it, and it made a difference.

1. 
   davcefai | Jun 16, 2009 07:02am | #10

   Marine chandlers also carry oxalic acid based products. (If you're near the sea).One word of warning, the oxalic acid may also bleach out some of the wood's natural colour so that you could end up with paler spots where the black was. Like the cosmetics bottles warn "test on a small area first". I once had a sailing dinghy where the deck was stained black around copper nails. I ended up with pale(er) spots around the nails instead.Tung oil followed by varnish mitigated, but did not totally remove, the problem.

1. 
   NietzschesMustache | Jun 17, 2009 03:58am | #11

   Thanks for the warning.