Oxalic Acid

Hi

I am currently restoring a boat which has badly discouloured (i.e. pretty much black) wood due to water ingress beneath the varnish. I am trying to get hold of some oxalic acid to try and sort this problem - Does anyone know where I can get hold of it in the UK?

 

See here - http://www.agwoodcare.co.uk/list_products.php?category=Bleaches%20and%20Acids

Also try searching for wood refinishers on the internet

If desperate, most 2 part teak cleaning products contain some oxalic acid (but fairly mild concentrations).

 

Most any decent drug store has oxalic acid, you'll probably have to ask for it. It's sold in crystaline form mixed with water. Works pretty well, though isn't fast.

Bill H.

 

I too have black stains (very black) on a spruce mast where water tracked beneath the varnish. I fear these stains are not just on the surface, but penetrate deeply enough that sanding would remove too much material.

To anyone who has tried straight oxalic acid solution:
1. How well does it work?
2. How deeply does it penetrate?
3. Can wood having been stained to black (presumably due to microbial action), and then treated in this manner, be considered to have maintained most of its strength at these regions?

Thanks for any help here.

Best,
Robert

 

Oxalic acid does indeed work. It does not always completely remove the stain but will reduce it considerably. We make a solution with water, brush it on and leave it to dry for a day. Some times we do this treatment 2 or 3 times for decent results. It does not penatrate very deeply and probably only affects the top 1/16 th inch(1.5mm) of wood. Clean the area well before varnishing. You'll find also that the grain is raised and fuzzy and will require a little sanding
As to those stains on your spruce spar, those are often first signs indicating fresh water ingress via fastenings and fittings which lead to rot and corruption very quickly. Usually you can guess where the water is entering by looking just uphill from the stain. You need to deal with it sooner rather than later or suffer some nasty consequences.