Oxalic Acid and Anodized Aluminium

[bob26]

I'm about to try Oxalic on my dirty teak woodwork for the first time having read about it here in multiple postings.

One I read mentioned that you should not get it on anodised aluminium. Can I ask why and what effect it has?

 

[BrendanS]

aluminium is reactive to acid. The anodisation provides some protection, but if you have any scratches, the acid is quickly through. Best to keep it off. It will get it clean pretty quickly though, so if any splashes, wash off with lots of water pretty quickly

 

[VicS]

As Brendan says the anodizing should stop any attack provided it is sound.
Oxalic acid is a relatively weak acid so any attack where the anodizing is damaged will not be rapid.

I am sure one forumite has said no problems but best advice must be to keep it away from the aluminium and wash any splashes off .

 

[Bosun Higgs]

Can't say I've ever noticed a problem. When I wanted to remove some anodising I had to use a really strong alkali. If I remember correctly , you use an acid as the electrolyte in anodising aluminium so I would expect the oxalic to have little or no effect. But in truth I don't know.

 

[MAURICE]

ive used it several times on my teak deck with no problems to my alum toe rail. I usually put it on have a cup of tea and then after 20 mins wash it all off.

Maurice

 

[rogerthebodger]

Don't know about aluminium but I have seen reports that using Oxalic Acid on polished stainless will dull the polishing over time and the Oxalic acid attacks the iron in the stainless.

Have no personal experience of this.

 

[alahol2]

Quote: Oxalic acid anodizing is similar to sulfuric acid anodizing with a few distinct differences due to the inherent properties of the acids. Oxalic acid does not attack and dissolve the forming oxide as aggressively as sulfuric acid. This lower dissolution rate allows for thick oxides (~2 mils) to be formed easily at ambient temperatures, a more dense oxide to form, and a smoother oxide surface to form. Parts anodized in oxalic acid are inherently colored due to the incorporation of oxalate into the oxide. This feature can be used to produce parts with a decorative gold or bronze finish. :Endquote

So it sounds like it will dissolve the anodising/aluminium.

 

[BrendanS]

It will, but that quote is about anodising under control conditions, which is a bit different to getting splashes on already anodised aluminium

 

[bob26]

Windows survive...

Well I tried the Oxalic and must say it brightened the teak up a treat....Dribbles from the toerail meant I also had to wipe the whole hull over or put up with white streaks in the normal brown waterline. The anodised fittings in range all seemed to survive unscathed (so far...maybe I'll go back later and find the window frames dissolved or something).