Dark Spots, tannin stains & discolouration of the wood surface are usually caused by moisture and is exacerbated when the moisture is contaminated with metal such as iron and steel (especially on Oak & Idigbo) and can be removed with oxalic acid.
Oxalic Acid can also be used to freshen wood colour if it has become lightly grayed due to external exposure to sun light. In the refinishing of wood furniture, oxalic acid can be used after stripping to lighten and soften darker stained areas before refinishing. It can also be used as a rust remover and a stain remover in many other applications.
Just hearing the word "acid" sounds ominous but oxalic acid is easy and safe to use in the home. In fact it is found in many vegetables including spinach, and rhubarb and is also used in shampoo and washing powders.
Oxalic Acid is supplied in crystal form and looks just like sugar.
How to use:- Simple mix with water as you would mix sugar in tea, in a clean container add the crystals to the water stirring until their is a little undisolved sediment floating around the bottom, you then have a ready to use saturated solution, (approx 60g to a pint of water) Adding more Oxalic acid crystals will NOT make the solution any stronger.
You could use Methylated Spirits instead of water. Using Methylated spirits allows for quicker drying enabling a protective coating to be applied to the timber sooner. Do not breath the fumes
Apply solution direct on to the timber with a brush, any surface coating such as woodstain, paint, wood oils etc will prevent the oxalic acid solution from working so all protective coating will have to be removed first.
The bleaching process will continue for 1 - 2 hours, but could remove the stains within 20-30 minutes. It may require multiple applications to fully remove the staining but once removed the timber will need to be thoroughly cleaned with clean water or meths and then allowed to dry.
One kilo of oxalic acid will make approx 8 - 9 litres of ready to use solution and with a coverage of 12sq meters per litre (depending on porosity of the timber)
Our oxalic acid is a high commercial 99% + purity grade, not all oxalic acid for sale are the same.
A pre mixed Oxalic acid Wood Bleacher is also available as a ready to use liquid in 150ml, 250ml, 1L, 2.5L & 5L
Always protect your skin and wear a dust mask when mixing.
Pack size: 1Kg, 5kg, 10Kg and 25kg sacks.