Oxalic acid and Redwood?

[Joe Wood]

I picked up this 4x4 and 2x6 B redwood yesterday and gave it a wash using Oxiclean to get the dirt and mildew, then an oxalic acid wash using 2 cups acid to a gallon of water. The 2x6 came out nice but what happened to the 4x4, it’s all black after the oxalic wash.
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Any remedy for this or do I need to sand it all out?

I'm reading up on it now and came across this rinsing Info which I've never done using oxalic acid before-
'Mix a neutralizing solution of ammonia and warm water, or Borax and warm water, in a plastic bucket and thoroughly rinse the wood surface.'

[Wayne Lomman]

It's most likely some form of contamination in the old timber. It may not sand out, in fact it looks quite deeply entrenched. What you see is what you will always have.

I am not in the habit of using any chemicals to clean timber but in this case I don't think it is your fault as the rest of the job is OK. If something must be cleaned, I recommend fresh water and a scrubbing brush or if it is really bad, use a pressure washer. Cheers

[Prashun Patel]

That looks more like fir than red oak to me.

But that black staining is common for red oak. It can happen upon exposure to iron. What did you use to apply the wash with?

[Joe Wood]

This is new Calif. redwood, and oxalic acid is also called a wood brightener or wood bleach and shouldn't have done this.

[Prashun Patel]

It is hard to bleach green red oak. Are these properly dried? The water in the lumber is your enemy for staining

[Joe Wood]

This is Calif. redwood not red oak and yes they are pretty dry.

[Wayne Lomman]

Guys, redwood, not red oak. Even this far away I still get to use redwood from time to time. Joe, I really don't think the oxalic acid did this without the presence of some other contaminant. If it is new timber, get back to your supplier and ask for an explanation as to why they shouldn't replace it. Cheers

[Prashun Patel]

Aha !!! Makes way more sense. I thought it looked like fir!!! Thanks, Wayne

[John TenEyck]

I used to clean my redwood fence with oxalic acid and it always made it bright and new looking again. So I have to think the piece you had that went wonky either is not redwood or is contaminated with something oxalic acid reacts with in a negative way.

John

[Joe Wood]

Yeah you see in the 1st pic the 2x6 and 4x4, both were washed the same. I'll probably end up planing it down a bit and routing the edges again, but will wait to see what my supplier says. Looks like iron stain but that's what oxalic is supposed to take care of.

[Joe Wood]

some better pics, the 2x6 is on the left.

[David Utterback]

Please let us know how it turns out. Thanks