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Using Oxalic Acid To Bleach Wood Floors

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If you've ever been in the middle of a refinishing project only to discover that the wood you've just uncovered has black marks and stains, or if you have weathered cedar or redwood that you'd like to brighten up, then you'll want to learn about oxalic acid.

Oxalic acid(otherwise known as dibasic acid, ethanedioic acid or acid of sugar) is an organic compound with the formula H2C2O4 and occurs naturally in several plants as oxalates; in its refined form it is poisonous and extremely corrosive, yet easy to utilize and is one of the safer products for wood bleaching if used properly. While excellent at removing dark water stains from wood, it also removes any chemical stain previously used on the furniture.

Iron, Water and Urine Stains
Rust and trace metals in water or pet urine can cause black or blackish-blue iron stains on wood. Oxalic acid is effective at removing iron stains, but it may take three or four applications to totally remove them. The dibasic acid method works only on bare wood, so you must strip all stains and coatings before applying it.

Weathering of Cedar and Redwood
Cedar and redwood contain naturally occurring resins called tannins. When wood containing tannins becomes wet, the tannin rises to the surface, where it causes black or brown stains. Dibasic acid is effective at removing tannin discoloration, but again must be applied to bare wood.

Small Applications
Begin by stripping old varnish, which may reveal stains. Use mild bleach on ink and chemical finish stains and oxalic acid for water stains, such as black spots and dark rings. Use drop cloths and sand away oil or remnants of varnish; sand in the direction of the grain. With a dry paintbrush, whisk away the dust, followed by a thorough rubdown with a tack cloth over the entire surface.

Combine 1 oz. oxalic acid crystals with 1 cup hot water in a larger plastic bowl to mix a "wash" and coat the entire surface to reach an even color. When the item is consistently bleached, use a clean sponge and warm water to wash away all of the acid. To counteract the acid still saturating the wood, dilute ammonia with water 1:1 and use a clean sponge to wipe the entire surface. Immediately rinse again with clean water using a sponge and let the furniture dry for two days.

Once the item is dried, use extra-fine sandpaper to gently sand the entire piece. Remove the dust with a clean, dry paintbrush, followed by a thorough rubdown with a tack cloth.

Safety Considerations
Oxalic acid is highly corrosive and toxic in its refined form; use rubber or vinyl gloves whenever you handle it. Hazardous gasses may cause health problems, so always mix and use it in a well-ventilated area. The crystal and sandpaper dust is potentially dangerous; use a dust mask and eye protection. Have a pail of rinse water available to flush your eyes or to wash away spills if needed.

Uriah Yang is the freelance writer for e-commerce website in the chemistry. is just a place for you to look for some chemicals! Our guidechem provide the most convenient conditions for the international buyers and let these leads benefit all the business people.

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