How To... - DIY Finishing - Finishing Techniques - Wood treatments

How to remove natural stains or stains from the surface of wood

Wood sometimes has unwanted natural staining or its natural colour is too dark to achieve a very light, almost white finish. Problems with the colour of the wood can also occur as a result of processing, but not due to natural causes. During drying, mechanical processing or sanding of the wood, stains or discolouration may appear and must be removed without affecting the natural colour of the wood. In the first case, the wood needs to be bleached, while in the second case it needs to be discoloured. Discolouring and bleaching are two different techniques, but the term bleaching is often used in factories for both methods.

wood bleaching
wood with stains
photo source:

Bleaching, a procedure that removes stains caused by various reasons

Fading is required when stains appear on wood due to contact with metals, staining solutions or adhesives. Less aggressive solutions are used to remove them. They act on the stains without changing the natural colour of the wood.

The solutions used for bleaching can be mixtures of diluents or weak solutions of acids or bases. No special precautions are needed for their use, as they are substances that are often used in the household. However, for safety, protective gloves and goggles should be used.

A commonly used solution is sodium hypochlorite, i.e. ordinary chlorine bleach. It attacks berries, solvent-soluble colours, but does not change the colour of the wood, nor does it attack pigment-based colours. This is the case for paints or staining solutions that are resistant to outdoor conditions (UV radiation from the sun in particular). Hypochlorite is used diluted with water, the dilution depending on how concentrated it is. Apply with a brush or sponge and wash the wood with water afterwards. For greater effectiveness, washing can be combined with sanding.

decolorization deck photo source:
deck bleaching
photo source:

Sodium hypochlorite can also be used when the wood has been attacked to a small extent by mould. Be careful, this is not the case for wood that has been attacked while still in the tree stage, standing or felled. Blue mould - as this type of mould is called - is a defect that greatly diminishes the qualities of the wood and can only be removed partially and with great difficulty. Hypochlorite also has no effect on mould that has developed during the drying of timber or mould that has penetrated deep into unprotected wood outdoors (decks, decks, fences). Hypochlorite acts on the thin layer of black mould that sometimes also settles on varnish-protected wood if the humidity is very high and the water stagnates (puddles). Blue mould is treated as a wood stain and can only be partially removed by bleaching with a concentrated 35% solution of perhydrol (hydrogen peroxide).

The superficial black stains caused by the contact of tannin woods with metals are removed by washing with weak solutions of organic acids. Use citric acid (lemon salt) or oxalic acid. Both are in solid form as white crystals and can be bought in DIY stores. The crystals dissolve in warm water and the resulting solution is used to wash the surface of the wood. Finally, the wood is washed with water. WARNING! Oxalic acid is an irritant, so wear gloves and glasses when bleaching. Subsequent sanding should be done very carefully because acid crystals may remain on the surface of the wood.

Resin stains on softwood or adhesives are removed by brushing with hot weak alkaline solutions such as ammonium bicarbonate solution (food ammonia). The surface is then washed with vinegar (acetic acid 5% or 9%) for neutralisation. Resin stains can also be removed by washing with organic solvents.

wood bleaching
bleaching of stains with oxalic acid
photo source:

Bleaching, a process used to remove natural wood stains

Wood bleaching is the process of attacking the colouring substances in the wood structure, partially destroying them. As a result, the natural colour of the wood is partially or totally changed, resulting in a lighter surface than the original one. Species that are frequently subjected to such treatments are fagul, oak treeeven nuc.

The most commonly used materials for bleaching wood are caustic soda (sodium hydroxide) and hydrogen peroxide (perhydrol), which can be used mixed or separately. If used together, the substances are mixed when bleaching is done. Another technique is to apply the two solutions successively, one on top of the other. Once the reaction is complete, if the proportions are respected, there is no need to wash the wood because the substances neutralise each other and turn into water and carbon dioxide. If only caustic soda is used for bleaching, great care and caution is needed because it is very corrosive. After application, the wood should be washed thoroughly with plenty of water.

Another method of bleaching is using perhydrol and an ammonia solution. Both are volatile substances and no residue remains after use and the wood does not need to be washed. The mixture is aggressive, and protective equipment - gloves, gown/jacket, goggles, mask - must be worn when using it.

The desired result is very rarely achieved in a single step, sometimes requiring several successive treatments of the wood. For some finishing requirements, the wood is treated until it is almost white. In this case chemicals are not sufficient and it is necessary to combine chemical treatment with the use of a white pigmented paste. This is how species such as maple, birch and poplar turn white.

Bleaching can also be used for artistic purposes. An example is the species wenge, whose colour is a mixture of light and dark brown and black. Bleaching only attacks the light brown fibre which changes colour to grey. Wenge bowls that have been bleached take on a special appearance reminiscent of African art.

wood bleaching
bowl from venge blanched
photo source:

The subsequent finish may be influenced by bleaching. Be careful when neutralising/washing the wood surface!

After staining, the wood should be left for 48 hours before finishing. This time is necessary for all volatile substances to disappear and for the wood to dry after washing with water. Although in most cases no residue remains, there are finishing materials that are influenced by the products used in bleaching. This is the case for polyurethane varnish catalysts, which visibly yellow when in contact with bleaching products. It is therefore not recommended that chemically bleached wood be finished with such primers/lacquers. Acrylic products are recommended. These are also recommended if we want a natural look of the wood.

WARNING! Regardless of the method, you should be aware that the substances used to bleach and/or bleach wood are aggressive and can cause harm. You should therefore wear protective equipment and protect your hands and eyes. A mask is also very important to avoid inhaling the fumes released in the process.

Further information can also be found in the articles bleaching and discoloration of wood after removal of the old finish or when discoloration and bleaching of wood is required.

I hope you find the above information useful. As usual, additions are welcome. And if you have any questions or queries, please leave them in the space below. I'm sure I'll reply.

About the author

Mihaela Radu

Mihaela Radu is a chemical engineer but has a great passion for wood. She has been working in the field for more than 20 years, wood finishing being what defined her during this period. She gained experience working in a research institute, in her own company, as well as in a multinational. She wants to continuously share her experience with those who have the same passion - and more.


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    • Good evening.
      Unfortunately lakes also "age" over time. They turn yellow and this is most noticeable in nitrocellulose lakes. The process is irreversible, so the safe solution is to remove the existing varnish and apply another layer of varnish. Removing nitrocellulose varnish is not difficult. It can simply be washed off with thinner. If you are unable to take it to a factory for varnish removal, you can also do it at home with paint stripper bought from DIY stores. Apply the varnish with a brush, leave it for a while, then remove it with a scraper. Then sand the wood and apply 2-3 coats of varnish. Acrylic varnish is the most resistant to yellowing.
      Good luck!

  • Hello, we have 90m2 of solid wood flooring. In the first phase it was light coloured and then we applied dark bait and varnish.
    Is there any chance of returning to the original colour?
    Will his defoliation affect the fault?
    Or did the bath penetrate the wood structure? How can we initiate the colour opening process?

    • Good evening.
      You should scrape it to remove both the lake and the bath. Being new flooring you should have no problems. The grout has penetrated the wood, but scraping removes a thin layer of wood, therefore removing the grout as well.
      After sanding, replace the sandpaper with a thinner one, sand and apply the new bait and varnish or just varnish.
      Unfortunately you don't have another way to open the color.
      All the best!

  • Good evening. I have a couple of windows that are blackened by time. How could I restore them, even just the fart, to their natural wood color? Thank you

    • Hello.
      From what you are saying I can't tell if it is the appearance of blackness on the windows or the darkening of the windows.
      If it's blackness then it's mould. It should be wiped well with a dry cloth and then with one soaked in cheap bleach. It is based on sodium hypochlorite, a mould enemy. It should remove that black colour and protect the wood for a while.
      If it is the wood darkening, it means that the varnish used had no UV protection and the wood components have decomposed darkening the colour. You should sand to remove the finish and the layer of darkened wood. Under this layer the wood has its normal colour. Then use for finishing products containing a small amount of pigment (lacquers) or UV absorbers (exterior varnishes) that protect the wood.
      All the best!

      Don't forget to subscribe to the printed Wood Magazine! For only 58 lei/year you can find out news in the field, discover craft ideas or trade secrets. We remind you that the content in the printed magazine is different from the one on the website. Details in the link below. 
      Thank you!

  • Hello. We recently built our house and unfortunately the interior oak stairs have suffered. They have yellowed and there are marks left from the workers gluing stuff on them in order to protect them. By the time they were stripped off there was trace left, probably also from the windows and the sun. How can we make them have the original colour and shape? If you give me an email address I can send you the picture. Thank you!

    • Hello.
      Wood changes colour in contact with oxygen in the air and UV radiation. The change starts immediately after cutting. And the lake changes colour over time, it ages, as we say. It's all the ozone and the sun or bright light that's to blame.
      more than likely the colour has changed in areas where it has not been protected from the sun. Now that the other areas have been uncovered the color will unoform over time. The easiest thing to do is to wait for this to happen because otherwise you have to remove the finish and sand the wood to remove the top layer that is affected. After that you can refinish. If you apply a coloured varnish on top to even it out it will not look nice and you will not achieve evenness unless the colour is very dark.
      You can send your photo to
      All the best!

      Don't forget to subscribe to the printed Wood Magazine! For only 58 lei/year you can find out news in the field, discover craft ideas or trade secrets. We remind you that the content in the printed magazine is different from the one on the website. Details in the link below.
      Thank you!

  • Hello,
    I have a big problem with interior doors. Unfortunately, I made some bad choices. I wanted the steps and doors in the house as dark as possible (almost black). The problem is that I don't know what products to use to clean the doors so that there are no marks left on them. Can you give me some advice, please? Thanks

    • Good evening!
      It's kind of hard, especially if they have gloss. Try applying a thin layer of colourless furniture wax on top. Apply simply with a rag. You just have to spread it very well. Waxed surfaces are easier to maintain.
      All the best!

      Don't forget to subscribe to the printed Wood Magazine! For only 58 lei/year you can find out news in the field, discover craft ideas or trade secrets. We remind you that the content in the printed magazine is different from the one on the website. Details in the link below.
      Thank you!

  • Good evening,

    I want to scrape the hardwood floors in my son's room.
    My question is if after refinishing can a bait or primer be applied to change the colour of the floor to a light grey (this is what my boy wants).
    Only then apply the varnish.
    Now the floor is brown and I don't think it has ever been scraped (old manor house).

    Thank you in advance

    • Good evening!
      Yes, you can bathe the wood after you scrape the floor. The scraping should be done in such a way that the old colour is removed. I recommend the use of a trowel for the application of the wood stain. Allow to dry before applying varnish. Then apply min 2 coats of floor varnish.
      All the best!

  • Good evening,

    I purchased 2 pieces of walnut lumber and they have some stains on them. I read the article but can't figure out if it's the traditional mold or the blue mold. Can I possibly send you some pictures to help me with this information? After the wood is cleaned with chlorine or hydrogen peroxide is there still a possibility that the mould will reappear if the wood is kept in a dry environment? In case of blue mold is 35% hydrogen peroxide and 65% water added? How long should this solution stay on the wood? Afterwards, do you just clean it with water or do you have to sand it?

    Thank you,
    Andrei Veres

    • Good evening!
      The blue mould is seen as a stain that is part of the wood fibre. It is not uniform, it can appear as if an annual ring is coloured. Regular mould is dark grey or black and no longer creates the impression that it is part of the wood but looks more like a stain. Regular mould is easier to get rid of than blue mould. When a wood is attacked by blue mould, changes in the wood's properties also occur, the changes are more profound, not just in colour. Blue mould is a wood disease.
      If the wood is well cleaned, dry, kept in a place without moisture and where there are draughts, black mould will not appear. Mould appears on wood as it does on the wall - if there is a source of moisture and no draught to allow it to dry.
      For blue mould you should try more aggressive solutions: caustic soda:pehidrol 2:1 (this is the classic A+B solution of commercially available wood bleach) or perhydrol and ammonia (solution 35%). Perhydrol and ammonia are not mixed but applied with a brush on top of each other. Apply hydrogen peroxide first, in excess, then apply the ammonia. After 2 hours wash off with plenty of water and allow to dry.
      The combinations of substances used neutralize each other and it is enough to wash with plenty of water to remove the resulting salts and let dry. If you use basic solutions (caustic soda) neutralize with weak acids (vinegar). Afterwards wash with plenty of water. There is no need to sand after bleaching with chemicals.
      You can send me photos to my email address
      All the best!

  • Hello! I have a white wooden table and a little girl has stained it with spirt and the shape of the tablecloth has printed, what can I use to remove it? Thank you

    • Hello!
      Try to tread on the surface. Place a piece of kneaded material on the surface and run a hot iron over it a few times. Pick up the material and let it cool. Check the area and if the situation seems to have improved, repeat the operation until the signs disappear.
      If it doesn't work with the iron, it means the area is more seriously affected. You should sand with 280 or 320 grit sandpaper or a fine abrasive sponge until the defect disappears. Afterwards polish the entire surface with a white furniture wax cloth. If the defect is deep and you have reached the wood or in the area where the sanding was done there is a visible hole, you will have to sand the entire table top and apply a coat of white nitrocellulose or water-based paint.
      All the best!

  • Hello
    A few years ago I scraped the floor and then applied 3 coats of Palux.
    Not long after (approx. 2 years) he was submerged.
    From the article I understand it is black mold.
    Please advise me what to do to remove the mould, apply a treatment to increase the resistance of the wood to water and mould, what finish to apply (please indicate which one).
    Thank you.

    • Good evening!
      There must have been cracks in the varnish film or the wood had pulled water from somewhere and mold had formed.
      Against mould you can find effective products at Bochemit.
      In order not to continually repair where black spots appear, you will need to scrape the entire package, treat it with Bochemit's solution against mold and mildew, and after drying, apply 2-3 coats of floor varnish.
      You should check that there is no source of condensation or dampness under the floor. Seek the advice of a flooring specialist (other than the first one) to see if it has been fitted correctly.
      All the best!


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