Refinishing redwood deck

[kaneohe]

We had a redwood deck installed some years ago. DW stained it. Within a year or so, it got very dark......almost black, and although not perfectly uniform, uniform enough that it was hard for me to believe that it was mildew, which for some reason, I associate w/ irregular patches.

I removed the blackness by mechanically sanding the deck w/ a small power sander and also some time-consuming hand-sanding in some deeper grooves that we had at some point created w/ our first experience with a power washer.

Right or wrong.....I did not believe at that time that the blackness was mildew (too uniform) or natural graying of the redwood (too black, too fast ). I instead thought it was something about the stain.

For the next go-arounds, I instead used Thompson Water Seal which seemed to be much better. It did not turn "instantly" black like that first stain but the process seemed to be a lot more gradual. After some number of years of rejuvenating w/ more of the same, the black stage again has arrived.
Although I rejected chemical treatments the first time around, I'm considering it this time.

My issue: what is the blackness and what treatment makes sense?

Chlorine bleaches are not recommended.

O2 cleaners are recommended for mildew and natural graying.
If I don't think it's mildew , is it reasonable to believe it would work.

Oxalic acid cleaners are recommended for redwood tanins but
they talk about these as being orangish...or at least something other than black. Is it reasonable to believe this would work.

I don't mind doing the power sanding but the blackness in the grooves from the earlier power washing is the part I don't relish doing again.......the grooves are deep enough that I wouldn't want to level the whole deck.

Suggestions welcome.

edit to add: DW went out and bought a power washer over objections from my still-alive (I think) body so now there are patches of bare wood and blackness. Will the chemical cleaners do harm to the bare wood?

 

[ERD50]

careful with the pressure washer, they can easily raise a lot of grain and bring up splinters and other bad stuff.

The oxalic acid cleaners are very good, I'd give that a shot. I kept the old jar of "Wolman' Brand that I used, as it was much easier to use than another one I tried. it changes color, and foamed, and just gave a lot of feedback that it was working. Some other brand it just sat there, and you couldn't tell until you washed it off, and then it was too late if it needed more time. Maybe the results are the same, but I just found Wolman's far easier to use.

Lucky for me, no real mildew problems on our decks now, and DW has decided she likes the natural, aged look better than stain. I ain't gonna argue!

-ERD50

 

[Westernskies]

Oxalic acid wash, scrub with a stiff bristle push broom, and a clear water rinse. A diluted coat of transparent oil-based (non-film-forming) stain will even things out. Put a few drops of a fungicide or chloriine bleach in the stain to slow down the mildew. Don't use Thompsons Water Seal (it contains silicone, nothing else will ever stick to it) Rinse and Repeat every couple of years- nothing will keep it looking completely new for very long; it is a losing battle. Redwood naturally oxidizes in sunlight; the surface oxidation and case-hardening protects the wood underneath-why a softwood like redwwod or cedar will last for years exposed to the elements when spruce, pine, or fir deteriorate in just a few years.

Or just let it gray naturally and learn to live with it.

 

[ERD50]

Don't use Thompsons Water Seal (it contains silicone, nothing else will ever stick to it)

Ah-hah!

Last year I added some wood steps to the patio door exit, and built a little privacy fence around the A/C and used a solid color gray latex stain on these (new pressure treated wood, allowed to dry out a while). I also stained the back door steps at the same time (pressure treated wood that had been stained, and probably Thompson'd as well along the way). The back door steps peeled up within a month, even though I gave them a good sanding first. The other new wood areas are fine.

Great, I may never get them to match now. I'm gonna try a thinned down stain, just to get some color in there, maybe oil would work better than latex for this.

-ERD50