Beautiful and durable, wood floors are an asset to any home. Not only do wood floors add resale value, but they also provide warmth and richness that few other floor coverings can hope to match. Yet stains in wood flooring can be difficult to eliminate or reduce. Water stains penetrate the wood and create lap marks. Iron stains that mix with wood tannins are particularly insidious because they penetrate so deeply and are so dark, nearly black. Rust, too, is another type of stain that latches onto the wood's cellular structure and is extremely difficult to remove.
Wood floors that are stained can often be successfully bleached to reduce or remove the stains. Bleaching differs from pickling because it is used to revive a floor and is generally not used as an antiquing or distressing technique. Oxalic acid is a good bleach to use on wood floors.
What Is Oxalic Acid?
Oxalic acid, inexpensive and readily available, is an organic compound derived from leafy green plants and vegetables like rhubarb. Available in powdered form and mixed with water, 99.6-percent pure oxalic acid is widely used as a safe bleaching agent for wood floors.
When working with chemicals to bleach a wood floor, make sure that the room is well-ventilated. Always wear waterproof gloves and eye protection when working with oxalic acid, and wear a dust mask when working with oxalic acid in dry form. Avoid touching oxalic acid with your bare skin. If you do come into direct contact with the acid, flush your skin with a steady stream of water for 15 minutes.
Equipment / Tools
- Waterproof gloves
- Eye protection
- Dust mask
- Clean plastic bucket
- Scrub brush
- Shop vacuum
- Random orbital sander
- Wood paint mixing stick
- Oxalic acid
- Clean water supply
- Fine sandpaper disc for the sander
One prime benefit of bleaching with oxalic acid is that it targets the stains while mostly leaving the wood's natural and dyed colors and composition intact.
If you want to alter the natural color of the wood, you will need a two-part bleach consisting of sodium hydroxide and hydrogen peroxide. If you want to alter the color of dyes or stains applied to the wood, then you will need to use chlorine bleach or dilute sodium hypochlorite.
Remove Protective Sealants
To fully bleach the wood, the bleaching solution must be able to reach the wood's cells. If the wood floor is painted, sealed, waxed, or coated with any type of protective layer, this layer must be removed. Sand down any part of the wood floor covered in a protective layer until you reach bare wood. After sanding, thoroughly clean all dust from the flooring.
Locate a Hidden Area for Testing
Ideally, you should test the bleaching mixture in a small hidden area of the flooring before you bleach the rest of the floor. Suggestions for areas of wood floor that are commonly covered up yet accessible include those areas under a floor-level heating register, in a closet, under wall-to-wall carpeting that is attached by tack strips (not by glue), under a floor transition strip, under any floating floor that covers the wood flooring, or under a baseboard.
Create the Bleaching Mixture
Mix 12 to 16 ounces of oxalic acid powder to 1 gallon of hot water in a clean plastic bucket. Mix thoroughly until all of the grains are mixed in. Since oxalic acid reacts when exposed to metal, be sure to use a plastic bucket only and do not mix with any metal implements. Mix with a wood stick or by hand (while wearing waterproof gloves).
Oxalic acid is a corrosive substance that could severely damage your eyes. Before opening the package to begin mixing, make sure you're wearing adequate eye protection.
Apply the Bleaching Mixture to the Floor
Dip the brush in the bucket and transfer the hot bleaching mixture to the floor. The mixture must remain hot in order to work effectively. Do not pour the mixture directly onto the floor from the bucket.
Scrub the Mixture on the Floor
With the scrub brush, scrub the bleaching mixture onto the floor. If the mixture in the bucket begins to cool, reheat the mixture. You should not have to scrub hard. Instead, let the bleaching mixture do the work.
Remove the Bleaching Agent
Wash off the bleaching mixture with equal parts clean water and white vinegar which will neutralize the bleach. In order to fully remove the water and bleaching mixture, vacuum it up with the shop vacuum and discard the contents of the vacuum.
Let Dry, Then Sand
Let the flooring completely dry, then lightly sand down the area with a random orbital sander and fine-grit sandpaper.
Repeat the Process
Bleaching wood flooring with oxalic acid is typically a multi-step process. It is normal to have to repeat the process several times until you achieve the desired results. Always finish bleaching wood floors by letting them completely dry out, then lightly sanding.