Black stains on white-oak chairs
I built two chairs of white oak last year, and they’ve got black stains on them that look like mildew. I just tried cleaning them with detergent and bleach with little improvement. Here’s the details:
- They’re outdoors all the time but under a porch roof.
- Finished with Watco teak oil
- The stains are only on the top sides of the backs and seats; nothing underneath
- The seat is slanted and does not accumulate water
- They’re exposed to direct sun for two hours in the morning until the sun is eclipsed by the porch roof.
- All the hardware is stainless steel, and the stains are not near it.
Before I try straight bleach, can anyone speculate on the cause of the stains and how to remove them? Should I add mildewcide to the next oil finish I put on them?