Oxalic acid?

MT

I'm trying to restore the colour in the mahogany surround of a sailing boat's seated area. I plan to remove the brown, yuk, paint and then stain the wood with a deep mahogany dye. The reason for doing this is that much of it has lost its colour and has gone very pale. However, before doing this I wan't to get rid of the blackish blotches that have developed as a result of watering getting in through the old coating; there are other stains and variations in colour that I also want to even out.

I've read that oxalic acid is a good bleeching agent for timber but don't know where to get it or if it works well on the likes of mahogany. Can anyone shed any light here or give me a brand name that the stuff is sold under? I've heard that Starbrite fibreglass hull cleaner contains oxalic acid but this only comes in small containers and is quite expensive. Is there a more economical option?

kadman

I would be extremely careful using oxalic acid crystals, as they are poisonous.
I would advise that you should do as much research into using an alternative approach to oxalic acid crystals. Personally speaking , giving this type of information across a forum is not always a good idea, as there is no guarantee that the instructions come across clearly , as there may be areas of misunderstanding in the process, leading to calamities.

It would be better to get one to one advise and guidance if you can. Failing this , I,ll research the extensive references I have from bygone woodfinishers books, and post them for you. Dodds of Mary Street used to be my supplier, hopefully there is still someone there who understands the uses of this.

I hope I have not come across as to condescending with my advise, I just cant emphasise enough how dangerous oxalic acid is.

kadman

MT

I've been busy lately so have only got around to getting back to this now.

Don't worry, your advice doesn't sound condescending in the slightest. I appreciate any viewpoint that takes safety seriously as there are enough accidents and mishaps in this world. I didn't even realise oxalic acid crystals were poisonous - is that to the touch or solely through inhalation of fumes? I've used Starbrite as a cleaner before and the crystals in it didn't seem to harm my skin. Might be a different matter if someone like a child swallowed them; I think I'm right in believing that Starbrite hull cleaner does contain oxalic acid.

Any info you have, Kadman, on the use of oxalic acid would be much appreciated; I was going to say PM me but then maybe putting the advice in this thread would benefit others as well as myself. Unfortunately, I'm notsure I know anyone with an experience of using the stuff so you seem to be my best shot at the moment.

chamac

A lot of cleaners including boat cleaners contain oxalic acid. Astonish and Vanish are two. Y10 boat cleaner has it too. Some people mix it with wallpaper paste to make it stick to the fibreglass.

magicbastarder

it's oxalic acid which makes rhubarb leaves poisonous. not much help to you, but there you go.

Jaffser

Oxalic acid can be ingested through contact with the skin along with the more normally accepted oral method. Studying chemistry at NUIM and have been warned of it.

http://avogadro.chem.iastate.edu/MSDS/oxalic_acid-2H2O.htm

Handle with care, or better still - don't handle at all!

A

recipio

You can buy Liberon bleaching fluid from good woodworking outlets. The results can be hit and miss - you may not remove old rusty stains for instance. I'd consider removing the boards and skimming them through a thicknesser ( if you can access one ) or replace with new mahogany? A boat deserves a classy finish !