How To Bleach Wood With Oxalic Acid?

Oxalic acid is a popular choice of bleach among woodworkers because it bleaches and removes stains from wood without altering the natural color of the wood. It is important to bleach wood correctly with oxalic acid to get the best result that this method can offer. This is how you would bleach with oxalic acid.

To bleach stains from the surface of wood, mix 28-30 grams of Oxalic acid crystals with one cup of hot water, and leave it to dissolve completely. Using a brush, apply the mixture on the surface of the wood you wish to bleach and leave it to dry, make sure to cover all the area evenly.  Once it has dried, neutralize the acid in the wood by washing it down with a solution of Borax and water. Finally, allow the wood to dry before sanding and finishing.

Bleaching wood is a sensitive procedure that requires caution and a bit of expertise. With the proper guidance, a newbie can begin to bleach like a pro. This article will take you through the ABCs of wood bleaching with Oxalic acid. We will also provide answers to all the questions you may have concerning wood bleaching. Read on!

How to Mix Oxalic Acid to Bleach Wood

Oxalic acid is packaged in a crystalline form which is usually dissolved in water before use. The ratio of oxalic acid to water depends on the need of the project. There are two ways of mixing oxalic acid for bleaching wood.

Oxalic Acid Wash

Oxalic acid wash is prepared to bleach a large surface of the wood without deep bleaching. To prepare the wash for a small wooden surface, mix one ounce (28 grams) of oxalic acid crystals with one cup of warm water. For larger surfaces, mix eight ounces of oxalic acid with one quart (950 ml) of warm water.

Oxalic Acid Paste

To prepare Oxalic acid paste, mix the crystals with a bit of warm water until it forms a paste-like consistency. The paste formed is often used for spot treatment of stains on wood instead of covering the entire surface of the wood with the acid.

The paste is applied to the wood, allowed to dry before it is scraped off. After scraping, a piece of cloth should be used to clean the wood.

Steps to Bleaching Wood with Oxalic Acid

To bleach wood with oxalic acid, you will need the following:  

  • Oxalic acid crystals
  • Hot Water
  • Spray bottle
  • A piece of brush
  • Rubber gloves
  • Borax

Step One: Clean the Wood.

The wood to be bleached should first be wiped with an appropriate wood cleaner. The purpose of cleaning the wood is to strip off any paint, wax, or finishing that may hinder the bleach from penetrating the wood.

TIP: Allow the wood to dry properly after cleaning before beginning to bleach.

Step Two: Mix the Oxalic Acid Crystals with Hot Water

To mix oxalic acid with water for bleaching, follow the following steps:

  • Fill a glass jar with two-third of hot water.
  • Add the Oxalic acid crystals to the hot water and slowly stir. We recommend Rockler Oxalic Acid for a proven good result.
  • Keep stirring and adding in more crystals until it begins to gather at the bottom of the jar.
  • At this point, you can stop adding the crystals because the solution is already saturated. Just shake it up and begin to use it.

Step Three: Apply the Bleach On the Wood.

Apply the Oxalic acid solution on the surface of the wood with a piece of brush. For larger surfaces like the floor, a mop will be appropriate for applying the solution.  It is essential to ensure that the solution covers the entire surface of the wood as this is necessary for the wood to bleach evenly.

Leave the oxalic acid solution on the wood till the desired level of lightness is reached. If the stain persists after drying, the process can be repeated three or four times until the result is satisfactory.

Step Four: Neutralize the Acid.

Before any finishing can be done on the bleached wood, the acid present in the wood has to be neutralized. Neutralization is achieved by flooding the wood with a mixture of water and Borax powder to neutralize the effect of the acid. The Borax in water serves as a basic solution that is capable of neutralizing the effect of the acid. Alternatively, baking soda can be used in place of Borax.

To prepare the Borax solution, mix two tablespoons of borax powder with one quart of water and apply it liberally all over the surface of the wood. To ensure complete neutralization of the acid, repeat the process up to three times.

Step Five: Rinse Off and Check for Residues.

After the solution dries off, proceed to rinse off with water. The rinsing process can be repeated as many times as possible. When the surface is completely dry after rinsing, run a dark rag across the surface of the dried wood. If the rag has any residue on it, rinse again with water. Continue to do so until the rag no longer contains any residue when run on the surface of the wood.  

Step Six: Sand The Wood.

After the wood has completely dried, some of the grains may appear coarse. To even out the grains and give them a finer appearance, sand with 120-grit sad paper, and then finish up with 220 grit paper for a smooth effect.

What Exactly is Oxalic Acid (and how it works)

Now that you know how to bleach wood with it, it would be helpful to understand what exactly is Oxalic acid. Usually, oxalic acid comes packaged in a crystalline form that is to be dissolved in hot water before use. When dissolved in hot water, Oxalic acid is completely activated.

Chemically, it is known as ethanedioic acid, a compound found naturally in certain plants. When Oxalic acid in the natural form is processed, it becomes inorganic and toxic. This form of Oxalic acid is famous for wood bleaching and commercially available for other uses.

When wood is exposed to water or metal for an extended period, blotchy stains and marks begin to appear on the wood. These blotchy stains are referred to as Iron oxide stains. They arise due to the reaction between tannin present in wood and trace iron oxide from metals or water.

Iron oxide stains are solely responsible for most stains in wood. Other stains may be caused by heat marks, inks, dyes, etc.

Oxalic acid has been shown to produce amazing results when used for wood restoration. It is a preferred choice of bleach because it removes all kinds of stains without tampering with the color of the wood.

Tips for Bleaching Wood with Oxalic Acid

Provided safety precautions are adhered to; Oxalic acid is one of the safest bleaching products available for use. When bleaching with Oxalic acid, here are some tips to keep in mind.

Always Clean the Wood Before Bleaching: Before wood is bleached, it should be thoroughly wiped with a piece of cloth and an appropriate wood cleaner. Cleaning the wood ensures that the bleach penetrates the wood without obstruction from surface coverings like paint and wax.

Do Not Mix Oxalic Acid with Any Other Bleach or Chemical: If Oxalic acid is mixed with any other bleach or chemical, it can react to produce toxic compounds or gases that are detrimental to the health.

Do Not Mix Oxalic Acid in A Metallic Vessel: When Oxalic acid is mixed in a metallic container, it corrodes the metal and causes leakage of the solution on other surfaces. Oxalic acid should be mixed in a ceramic or glass container.

Always Use Protective Gears: Oxalic acid is a strong acid; therefore, contact with any part of the body might be toxic. Protective gears like rubber gloves, eye google should be worn before handling the acid. It is also safer and wiser to wear a long-sleeved shirt and long pants while working, as this reduces the possibility of direct contact with the skin.

Also, since Oxalic acid comes in a crystalline/powdery form, it can be easily inhaled while handling. Exposure to dust can lead to bleeding in the lugs. To avoid this, wear a dust mask while handling the powder.

Don’t Mix Oxalic Acid Ahead of Time: Oxalic acid is more effective when it is immediately mixed and applied to wood. If Oxalic acid is mixed ahead of time, it tends to become weak and less effective.

Work in a Well Ventilated Space: since oxalic acid is a strong chemical, it is safer to work in a large and well-ventilated space. The space should be large enough to allow easy movement while carrying out the work.

Alternatives to Wood Bleaching

If you don’t wish to pass through the stress of bleaching wood, other methods can be used for removing stains and restoring an old piece of furniture or wood.

For Really tough stains

  1. White vinegar and bicarbonate of soda: Add a few drops of white vinegar to baking soda and mix until a paste-like consistency is formed. Rub the mixture on the stain and wipe it off with a damp piece of cloth. This mixture is effective for removing dyes and other similar stains.
  2. Sandpaper: Stains that seem resistant to bleaching can be sanded. With fine sandpaper, gently sand out the stain and its surrounding areas. If need be, sand out the whole surface area to keep the color even.
  3. Isopropyl alcohol: Isopropyl alcohol is effective for clearing out stains like pen and ink. Using an old clean cloth, rub isopropyl on the surface and wipe out thoroughly. Once the stain is gone, clean the wood with a damp soapy cloth and allow the surface to dry.

   For less tough stains

  1. Petroleum jelly: Apply petroleum jelly on watermarks and allow to sit overnight before wiping off.
  2. Baking soda and non-gel toothpaste: For heat marks on wood, combine non-gel toothpaste and baking soda. Rub the resulting paste on the wood with a cloth till it begins to feel warm before wiping off. Keep repeating the process until you are certain the stain is completely gone. Smoothen out the wood with oil or polish it after.

Other Uses of Oxalic Acid

Oxalic acid is a household chemical used for various purposes. Apart from being a wood bleacher, Oxalic acid has other essential household and commercial uses. Some of which are;

  • For rust remover: Oxalic acid is a significant ingredient in many commercial rust removals. It is used to remove rust from pipes, sinks, metals, etc.
  • It is a bleaching agent for straw hats, stones, leather.
  • It is used as a laundry rinse and calcium removal.
  • It is used to remove paints and varnishes.
  • It is used as a mordant in the manufacture of textiles. it is also in the manufacture of ink.
  • It is used as a mild hydrolyzing agent in the preparation of dyes.

Final thoughts

Oxalic acid is great to bleach your wood and remove stains. It is not too expensive and if done right get’s the job done very well. We hope you learned something new from today’s article, if you want to read more useful guides on wood working be sure to surf our website a little more.

Martin Swizz

Hi! This is Martin, I like to research, experiment, and learn new things related to wood carving and other kinds of woodworking.

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