Oxalic Acid

Liquids, like water or pet urine, can seep into a wood floor and leave a brown or black stain. Bleaching the stain with a heated mixture of water and oxalic acid will remove the stain, leaving the natural wood colour. Oxalic acid is also useful to bleach stains on wood furniture, like those caused by a beverage container that left a water ring. Clean the surface to strip waxes and oils before applying oxalic acid to bleach a wood stain.

• Oxalic acid crystals or powder
• Hot water
• Borax

1. Clean the wood thoroughly with wood cleaner and strip all paint and finish down to the bare wood.
2. Mix the oxalic acid with the recommended amount of hot water. For stains: use 12 to 16 ounces of acid per gallon of water.
3. Apply the mixture liberally to the stain using a brush, mop or rag, depending on the size of the job.
4. Let the acid dry completely. If the stain remains, continue with further applications of acid, letting it dry completely between stages.
5. Mix 2 tbsp. of borax for each quart of water and apply to the wood after the stain has been removed or the wood has been bleached to the desired colour. This will neutralize the acid.
6. Allow the borax to dry. Rinse the floor thoroughly and allow it to dry.
7. Rub a clean dark cloth over the wood. If there is white powder residue on the floor, rinse with water again and allow the floor to dry.
8. Sand the wood lightly to smooth it after all remnants of the bleach has been removed.

• No one wood bleach works with all stains. Look to see which kind of bleach is the most effective for your type of stain. If you are unsure what caused the stain, try oxalic acid first. If it is completely unsuccessful, then consider other types of bleach like an A/B or chlorine bleach.
• If the bleached area becomes greyish-white, rub very fine steel wool over the stain to lift the light discoloration.
• Using oxalic acid to bleach wood stains is a better choice than household bleach, which can give the wood a greenish-yellow tint.
• Only use oxalic acid in a well-ventilated area. Keep kids and pets away and wear protective clothing.