January 11, 2023

Bleaching wood with oxalic acid

Bleaching wood with oxalic acid is a process used to remove discoloration or stains from wood surfaces. It is a common technique used to restore wood’s natural color or prepare it for further finishing or staining. There are several reasons why someone might want to bleach wood with oxalic acid, such as to remove dark stains or discoloration caused by water damage or sun exposure, to lighten the color of wood that has darkened over time, or to prepare wood for staining or refinishing.

Bleaching wood with oxalic acid is a relatively simple process that can be done at home with the right tools and materials. However, care should be taken when working with oxalic acid, as it can be harmful if ingested or inhaled. In this article, we’ll give you step-by-step instructions for bleaching wood with oxalic acid and discuss some of the possible results and benefits of the process. Whether you want to restore the natural beauty of your wood surfaces or prepare them for further treatment, bleaching wood with oxalic acid can be an effective and inexpensive solution.

How to bleach wood with oxalic acid

  1. Strip the surface so that there will not be any finish or wax blocking the penetration of the bleach.
  2. Dissolve the crystals in hot water until no more will dissolve. What tells you that they have dissolved enough is that they sink to the bottom. Brush the solution whilst hot over the entire surface.
  3. Allow the solution to dry back to crystal form. Wash off the crystals with a hose, sponge, or cloth. Brushing the crystals into the air will make you cough and choke if you breathe them. Wash the surface several times to remove all the crystals and neutralize the acid in the wood.
  4. Further, neutralize the acid by adding baking soda or household ammonia to water. You can finish wood with just a water-neutralizing rinse. 
  5. A second or third application of the oxalic-acid solution to the wood after it has dried helps with stubborn stains. Use an artist’s brush. If a light brown mark remains, sand it out. You may need to coat it three or four times, allowing time to dry between coats. Once the stain is gone, you can sometimes get an effect around the area where the wood stain was bleached. To remove this, saturate a rag with the acid solution and wipe a thin coat over the wood stain and surrounding area. Allow drying. 
  6. Once the stains are gone, neutralize the acid so it will not react with your wood finish. Mix up two tablespoons of oxalic in a quart of hot water. Saturate a rag with the oxalic solution, wipe the floor, and dry it. 

How long to leave oxalic acid on wood

Leave oxalic acid on wood for 1 – 2 hours. However, results can be seen within 20-30 minutes.

Oxalic acid mixing ratio for wood

Mix one part oxalic acid with six parts warm water. Apply a mixture to the timber using a brush or sprayer. Mix 28-30 grams of Oxalic acid crystals with one cup of hot water and leave it to dissolve.

Oxalic acid wood bleach before and after

Before you start with bleaching, there are factors to consider. Bleaching helps if your piece is blotchy or discolored. A new stain will do the trick. It does not matter if you are an inexperienced woodworker since bleaching is not difficult.

Amongst the tips you should follow, know the types of bleach available at your grocery store and their degrees of effect on wood furniture. Laundry bleach or chlorine will remove stain or dye color from wood but will not affect the wood’s natural color.

A/B peroxide-based bleaches like sodium hydroxide and hydrogen peroxide cause a chemical reaction that creates bleach that will blanch the stain color and can alter the color of the wood itself. Oxalic acid will remove water and rust stains, teak stains, and lighten the greying effect of weather-exposed wood.

Wipe your wood down with water or mineral spirits on a clean, soft rag before you bleach. Go over every surface with a dry cloth. Wait a day or two for it to dry before bleaching. Once bleached, neutralized, and dried the wood, the grain becomes coarse. Sand it with 120-grit sandpaper, then finish it with 180- or 220-grit paper for a smooth finish.

After coating your surface, mix two tablespoons of Borax with 1 quart of water. Use the mixed solution to wipe down the wood you bleach once the Oxalic Acid dries. You can also neutralize it with a 50-50 solution of white vinegar and water. Rinse with warm water and let the wood dry for three hours before you decide to have another application. Also, wash the surface several times to be sure you have removed all the crystals. 

Zinsser Wood bleach

It is a wood brightener on new or stripped interior wood surfaces to lighten the wood. Expect a more uniform color. The formula is powerful enough to bleach and brighten all wood surfaces, bringing out the natural beauty of wood. For effective results, apply two solution processes and let it stand overnight to dry and sand.

It is easy to apply on wood and works on most stains and finishes. Before application, test in an inconspicuous area and follow instructions. For use, allow the solution to sit for 5 to 10 minutes. After 5 or 10 minutes, pour the solution into the second plastic or glass bowl. Use a new sponge and soak it up. Rub it on the wood, again soaking it.

How to neutralize oxalic acid on wood

Add a little baking soda or household ammonia to water and wash with it. Oxalic acid is neutralized by rinse water. For better results, use a weak solution of water, baking soda, or household ammonia. 

Borax neutralizes oxalic acid

To neutralize the Oxalic Acid solution with Borax, mix two tablespoons of Borax with 1 quart of water, then apply the mixed solution over the surface. It helps ensure a safer working environment and reduces injury risks as you complete your project. Once the solution dries, rinse the surface with water.

How to use oxalic acid on hardwood floors

  1. Mix one part oxalic acid with 6 parts warm water.
  2. Apply a fair amount of the mixture to the timber using a brush or sprayer. 
  3. Use the scrubbing brush to scrub the stains.
  4. Allow drying. The timber will dry without stains.

Lye and hydrogen peroxide wood bleach

The sodium hydroxide and hydrogen peroxide mixture produce a strong oxidizer called sodium peroxide (Cdc.gov). Add 1.5 teaspoons of lye crystals to 1/2 cup water and keep in a well-marked plastic container with a plastic lid. Always add the crystals to water, not vice versa. Use the 27% hydrogen peroxide as it is.

Pay attention to personal and property protection since these chemicals are dangerous. For application, mix equal parts of the lye solution and hydrogen peroxide in a plastic or glass container and apply to the wood to be bleached using a cheap brush or dipping. Allow drying as the solution looks bubbles.

Results differ depending on wood species, wood preparation, and grain orientation. When bleached, apply household cleaning vinegar to neutralize the lye, although the step is optional.

David D. Hughes

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