Damages caustic soda metal

If many layers of paint and varnish take away the natural charm of a cupboard, table or door, this can be restored by leaching. The condition is that it is real wood. The following do-it-yourself instructions can be found in the following do-it-yourself instructions to understand what is meant by waste caustic, which work steps are required and whether the effort in connection with the costs is worthwhile.

Waste liquor - definition

Leaching, also known as stripping, is a chemical treatment of real wood in which layers of paint and varnish are removed from the wood. When stripping, a distinction is made between alkaline / leaching and solvent stripping agents. Leaching is an alkaline method. Stripping / leaching agents are usually provided with wetting agents and thickeners. Thickeners ensure a firmer consistency, so that the leachant adheres better to the wood when used and does not drip onto the floor when used vertically on, for example, doors. The wetting agents determine the effectiveness of the product. Depending on the wetting agent, they lower the surface tension of the paint and varnish solvent. In this way it is possible to get through several layers of lacquer and paint.

The alkaline stripping lyes include
  • Soda and potassium hydroxide
  • Ammonia water
  • Calcium oxide
  • Sodium, calcium and potassium carbonate
  • Potassium silicate
Possible thickeners can be
  • Paste or glue
  • pumice
  • talc
  • Sawdust or pebble flour
  • Strength
Suitable wetting agents are available
  • Alkylaryl and fatty alcohol sulfonate
  • "Rei" detergent powder
  • Soap and soap root extract
  • Washing-up liquid like "Pril"
TIP: Leachants are commercially available as a finished product in the form of pastes or as a powder for mixing. You save the search when buying the individual components.

Suitable types of wood

In theory, all types of real wood are suitable for leaching. For some, this discoloration process causes undesirable discoloration in the wood. Oak is one of these real woods, which, due to the large number of tannins it contains, can get gray or brownish discolouration through leaching. Thorough rinsing after stripping does not always remove this discoloration. For this reason, an invisible place should be tried out in advance to see whether the wood is suitable for stripping.

Leaching agent effect

When stripping with alkaline leaching agents, fatty acid-containing coatings are saponified. The solid paint and varnish is then liquefied and runs off or can be soaked up with an absorbent cloth / sponge. For this reason, leaching agents only work with oily paints and varnishes, as well as with alkyd resin varnish, which are often found on antiques or the wood of old houses. A leaching agent has no effect on emulsion paint or acrylic varnish. Solvent-based paint strippers are to be used here.

Difference to solvent-based paint strippers

Solvent-based paint strippers contain special organic substances such as gasoline, acetone, methanol or dichloromethane. They "eat through" the layers of paint and varnish so that they detach from the wood and can then be removed. As a rule, gases are released during use, which can cause serious health problems, especially when inhaled. For this reason, paint strippers containing solvents should only be used if another type of paint and varnish removal is not possible. It is advisable to wear a respirator during use.

Difference to color removal by sanding

Sanding can be an alternative way to paint and varnish removal if present in one layer. The old cupboard from the beginning of the 19th century has experienced many different color trends. In the fifties vanilla yellow dominated, in the seventies bright orange was modern, in the next decade dark green dominated the interior design, while black, gray and white with splashes of color and natural wood are currently prevailing. The cabinet and doors were usually repainted on top of the previous coat, so that several coats of paint would have to be removed with sanding. This takes a lot of time and effort and costs a lot of sandpaper, because the sanded off color immediately settles in the sandpaper and the grain is minimized. In comparison, alkaline stripping is noticeably more effective, cheaper and less labor-intensive.

Make your own caustic soda

In some cases, paint strippers from the trade prove to be ineffective. In order to ensure a sufficient effect, it is advisable to prepare a sodium hydroxide solution yourself. To remove lye, you can quickly prepare a sodium hydroxide solution yourself in conjunction with household remedies. It is important to take protective measures such as gloves, eye and respiratory protection and an apron, as caustic soda is very corrosive. Careful handling and a solid, stable base for the preparation of lye are required. The advantage of doing it yourself is that you can use simple home remedies. The home remedies you need can be found in every normal household and usually do not have to be bought separately.

  • 100 grams of 10 percent caustic soda (sodium hydroxide)
  • One liter of water
  • Approx. 200 grams of thickening agent such as starch or wallpaper paste (amount can be changed depending on the desired consistency)
  • Half a handful of mesh if necessary (not absolutely necessary)
  • A metal bucket
  • A wooden stick to mix
TIP: An increased amount / concentration of caustic soda does not increase the effectiveness and does not accelerate the process. Due to the caustic properties and possible white residues on the wood, the stated dosage should not be exceeded.

  • Fill the metal bucket with water (metal, because a chemical reaction creates heat)
  • Add caustic soda slowly and evenly
  • Important: the caustic soda has to be poured into the water and not the water into the baking soda
  • Stir
  • When the lye has cooled down, slowly sprinkle in thickener while stirring
  • Check consistency in between
  • If a wetting agent is used, stir it in before the thickener has cooled down
  • Mixture is ready to use when the desired consistency is reached

Materials required for leaching

In addition to the leaching agent, the following materials should be available for stripping:
  • Spatula or special paint and varnish strippers
  • Narrow woodworking chisel
  • Scratch brush made of metal
  • Plastic or scrub brush
  • Brush with plastic bristles or plastic sponge
  • Old cloths / rags
  • Chemical application gloves
  • Mouth and eye protection
In addition, the following utensils should be close at hand:
  • Bowl of clean water, garden hose, or pressure washer
  • One liter of water with a splash of vinegar essence

Work steps for leaching

First step
Spread leaching agent on the colored surfaces with a brush or a plastic sponge. Even mixed caustic soda is applied generously. If the moisture on the paint surface subsides, caustic soda has to be reapplied until a solution of the paint can be seen. If there is no noticeable success or if too few paint spots come off, the process can be repeated. It is important to ensure that the entire surface is covered again with the leaching agent. In this way, color differences in the wood are avoided.

Second step
Depending on the effectiveness of the leaching agent, it takes around five minutes for the paint / varnish to come off. Any particles that are still stuck are removed with a stripper, a spatula or a wire brush. Paint residues can be stubborn, especially in corners. These can be removed carefully with a sharp chisel or chisel even after they are completely dry. Since this can hide a different color of wood, the chisel / chisel method should not be used in too many places. A renewed leaching of the entire wood surface would then be necessary to compensate for the color differences.

Third step
Clean the leached area generously with water using a brush. Cleaning with a high-pressure cleaner is most effective with high cleaning power. Care must be taken here to ensure that excessive water pressure does not damage the wood. A high-pressure cleaner should be avoided, especially with soft woods such as spruce or pine. This could make dents in the wood like a milling machine. If water accumulates in corners, for example, this must be dried continuously.

fourth step
After cleaning with water, we recommend a follow-up treatment with vinegar essence. Leached surfaces are rubbed off with this. In this way, there is a further cleaning effect, lye residues are neutralized and the odor that is caused by the chemical reaction is minimized.

Fifth step
In the last step, the wood must be allowed to dry slowly. Complete drying can take up to 1.5 months. Accelerated drying using artificial heat sources such as a hair dryer should not be used. This could lead to tension in the wood, cause cracks and negatively affect proper functionality such as drawer openings or door closings due to the contraction of the wood. Glued strips could come off.

Lye bath

One leaching method is the lye bath. As a rule, this is used by specialist companies that deal with wood to be stripped on a daily basis. In the private sector, the immersion bath is suitable when many smaller objects with many corners are to be stripped. In order to immerse doors or large cupboards in a lye bath, a huge plunge pool would have to be available, which is usually not available in private households. These acquisition costs alone would go beyond an acceptable framework.


Ready-to-use lye and mixed products are available in every hardware store. In online do-it-yourself shops and specialist retailers for cleaning agents, caustic soda can be purchased for self-production, among other things. In terms of price, they are cheap and as follows:
  • 250 milliliters of caustic soda - from 2.50 euros
  • 500 milliliters of caustic soda - from 4 euros
  • 1 liter of caustic soda - from 7 euros
  • 2.5 liters of caustic soda - from 12 euros
  • 1 liter of ready-to-use liquor - from 10 euros
  • 10 liters of ready-to-use liquor - from 70 euros
  • 20 liters of ready-to-use liquor - from 130 euros

Costs for specialist companies

Compared to the costs incurred with DIY waste liquor, the costs for commissioning a specialist company are significantly higher. These vary from company to company, so the following price information is for guidance only.
  • Chests of drawers with a maximum width of 80 centimeters - from 130 euros
  • Wooden chests with a maximum width of 60 centimeters - from 70 euros
  • Tables with a maximum width of one meter - from 120 euros
  • Benches with a maximum width of one meter - from 120 euros
  • Chairs without armrests from 50 euros - with armrests from 70 euros
  • Buffet cabinet with a top up to 140 centimeters wide - from 220 euros
  • Buffet cupboard without top unit up to 140 centimeters wide - from 180 euros
  • Room doors up to two square meters in size - from 110 euros
  • House doors up to two square meters in size - from 180 euros
  • Shutters - around 50 euros per square meter
  • Stair railings - an average of 10 euros per running meter