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-   -   Clear Heart Cedar turns black (http://www.diychatroom.com/f4/clear-heart-cedar-turns-black-154375/)

DMAGNER 08-21-2012 12:03 PM

Clear Heart Cedar turns black
 
Hi all, new poster here, looking for some good advice on maintaining my clear cedar siding, as it is turning black in many areas just days after bleaching and re-staining it. It is a lot of work that seems to be going for naught, so I'm reaching out for some advice to get a pleasing result and get rid of the black.

Here's what I did to clean and restain the cedar:
Bleach 50/50 water (15-20 min)
Rinse with power washer (500-600psi)
Oxalic acid 1lb/1gal water sprayed on till saturated for 30 min or until lightened
Rinse well, neutralize with a basic solution
Dry for 2 days
Apply TWP 1351 oil base stain

The south side of the house seems to be holding up well, although in a few years it darkens and appears dirty, but the east wall is turning black again just days after bleaching and re-staining. I also noticed that on the west wall, where we have some knotty cedar from the original construction that we had stained 12 years ago still looks good, but a small section where we filled in with the clear heart cedar right next to it on the same wall is almost completely black.

For this section we used:
Olympic transparent stain
(with the same bleaching and cleaning process from before)

Any ideas on what is causing the black? It is probably mold, but why does it show up just a few days after bleaching and staining it, and why is it more prevalent in the clear heart cedar than the knotty cedar? Finally, what's the best plan of action to maintain and care for the siding in the future?

joecaption 08-21-2012 12:14 PM

Are there any exposted steel fastners where it's happening?

CaptRandy 08-21-2012 12:18 PM

What is a basic solution? If it is indeed a base(NaOH) type solution it is bringing out the tannins, reapply oxalic. Bleach is never a good idea for wood.......

DMAGNER 08-21-2012 12:45 PM

Quote:

Originally Posted by joecaption (Post 993432)
Are there any exposted steel fastners where it's happening?

The garage door has steel fasteners on the back, but they are 2-3 in away from the surface of the cedar. The rest of the wall on that side has no exposed steel, and is also turning black, but not as black as the garage door. There is a garage door on the north wall that is not affected.

The basic solution, sodium hydroxide, was not used on this section. It is part of the directions for the process, so I included it in the post, but wasn't really used throughout. Could not having used it also be the problem?


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