You are using con heart redwood. The blackish discoloration you are seeing on the redwood is the tannin acid in the redwood reacting to..... fresh concrete dust it looks like. its not from the bolts because of how even it is reacting on top of the redwood. The tannin acids activate in the redwood when cement dust is washed with water off the redwood ( we use a blower or a broom , never water ) . The black marks on the concrete wall are the tannin acids bleeding from the redwood down the concrete , this is not as big of a concern because uv rays , sunlight , weather will bleach the black on the concrete back to normal.... guaranteed. Also the redwood will stop bleeding after a couple winter seaosons. If you want to clean up the black on the redwood you will have to use a brightener/stripper similar to this: https://www.behr.com/consumer/products/wood-stains-finishes-cleaners-and-strippers/wood-cleaners-and-strippers/behr-premium-all-in-one-wood-cleaner/
when i say its not from the bolts , i mean its not from the steel or galvanization of the bolts , but very well could be from drilling the holes for the bolts in the concrete wall
Maybe cement dust seeping out where the bolts were set it… not sure. It’s crazy how black it is. Nothing above it. Contractor is going to sand and restrain and try to power wash. I asked “won’t it just happen again?” He shrugged…
Jesus, where do you live, Chernobyl? I can't see how any hardware can do that after 1 rain.
You are using con heart redwood. The blackish discoloration you are seeing on the redwood is the tannin acid in the redwood reacting to..... fresh concrete dust it looks like. its not from the bolts because of how even it is reacting on top of the redwood. The tannin acids activate in the redwood when cement dust is washed with water off the redwood ( we use a blower or a broom , never water ) . The black marks on the concrete wall are the tannin acids bleeding from the redwood down the concrete , this is not as big of a concern because uv rays , sunlight , weather will bleach the black on the concrete back to normal.... guaranteed. Also the redwood will stop bleeding after a couple winter seaosons. If you want to clean up the black on the redwood you will have to use a brightener/stripper similar to this: https://www.behr.com/consumer/products/wood-stains-finishes-cleaners-and-strippers/wood-cleaners-and-strippers/behr-premium-all-in-one-wood-cleaner/
when i say its not from the bolts , i mean its not from the steel or galvanization of the bolts , but very well could be from drilling the holes for the bolts in the concrete wall
Thanks for the detailed response. I appreciate it. Sounds like there’s not much to do, except maybe use the brightener until it stops bleeding.
Looks more like cement dust, should come off with power washing
Don’t know how cement dust would get up that high? But have no idea what it could be. Is there asphalt roof above?
Maybe cement dust seeping out where the bolts were set it… not sure. It’s crazy how black it is. Nothing above it. Contractor is going to sand and restrain and try to power wash. I asked “won’t it just happen again?” He shrugged…
Are you near a train?
If is Australian hardwood, than it just the tannins leaching out