Paint stripper

Paint remover is applied to an aircraft's landing gear during an inspection looking for cracks in the aluminum

Paint stripper or paint remover is a chemical product designed to remove paint, finishes, and coatings, while also cleaning the underlying surface. Chemical paint removers are advantageous because they act on any kind of geometry and they are cheap. They can however be slow acting.

Paint can also be removed using mechanical methods (scraping or sanding) or heat (hot air, radiant heat, or steam).

Types

The selection of chemical paint removers is based on the chemical bonds that form the paint's binder. the b work only on certain types of finishes, and when multiple types of finishes may have been used on any particular surface, trial-and-error testing is typical to determine the best stripper for each application. Two basic categories of chemical paint removers are caustic and solvent.

Caustics

Caustic paint removers, typically aqueous sodium hydroxide (also known as lye or caustic soda), work by breaking down the chemical bonds of the paint, usually by hydrolysis of the esters that comprise the paint film. Caustic removers must be neutralized or the new finish will fail prematurely. In addition, as caustic paint strippers typically include corrosive active ingredients, several side effects and health risks must be taken into account in using. Caustic aqueous solutions are typically used by antique dealers who aim to restore old furniture by stripping off worn varnishes, for example.

Solvents

Solvent-base paint strippers can be complex mixtures of various organic solvents, emulsifier]]s, thickening agents, alkaline or acid active ingredients as well as evaporation and corrosion inhibitors.Dichloromethane, also called methylene chloride, was once a popular solvent, but its use has been declining because of health concerns. Traditional solvent paint strippers penetrate the layers of paint and break the bond between the paint and the object by swelling the paint.

Paint strippers come in a liquid, or a gel ("thixotropic") form that clings even to vertical surfaces.

Alternative solvents

Solvent strippers may also have formulations with limonene from orange peel (or other terpene solvents), n-methylpyrrolidone, esters such as dibasic esters (often dimethyl esters of shorter dicarboxylic acids, sometimes aminated, for example, adipic acid or glutamic acid), aromatic hydrocarbons, dimethylformamide, and other solvents are known as well. The formula differs according to the type of paint and the character of the underlying surface. Nitromethane is another commonly used solvent. Dimethyl sulfoxide is a less toxic alternative solvent used in some formulations. Unfortunately, these alternative stripping formulas are largely ineffective compared to those based on dichloromethane - removing only one layer at a time, or often no paint at all. When they do work they take hours, compared to minutes or seconds for dichloromethane-based strippers.

Other components

Various co-solvents are added to the primary active ingredient. These assist with penetration into the paint and its removal and differ according to the target paint. Ethanol is suitable for shellac, methyl ethyl ketone is used for cellulose nitrate, and phenol and cresols are employed in some industrial formulas. Benzyl alcohol is used as well.

Activators increase the penetration rate; for dichloromethane water is suitable, other choices are amines, strong acids or strong alkalis. The activator's role is to disrupt the molecular and intermolecular bonds in the paint film and assist with weakening this. Its composition depends on the character of the paint to be removed. Mineral acids are used for epoxy resins to hydrolyze their ether bonds. Alkaline activators are usually based on sodium hydroxide. Some cosolvents double as activators. Amine activators, alkalines weaker than inorganic hydroxides, are favored when the substrate could be corroded by strong acids or bases.

Surfactants assist with wetting the surface, increasing the area of where the solvent can penetrate the paint layer. Anionic surfactants (e.g., dodecyl benzenesulfonate or sodium xylene sulfonate) are used for acidic formulas, cationic or non-ionic are suitable for alkaline formulas. Paint strippers containing surfactants are excellent brush cleaners.

Thickeners are used for thixotropic formulas to help the mixture form gel that adheres to vertical surfaces and to reduce the evaporation of the solvents, thus prolonging the time the solvent can penetrate the paint. Cellulose-based agents, e.g., hydroxypropyl cellulose, are commonly used for mixtures that are not extremely acidic or basic; under such conditions cellulose undergoes hydrolysis and loses effectiveness, so fumed silica is used for these instead. Another possibility is using waxes (usually paraffin wax or polyethylene or polypropylene derivatives), or polyacrylate gels.

Corrosion inhibitors are added to the formula to protect the underlying substrate and the paint stripper storage vessel (usually a steel can) from corrosion. Dichloromethane decomposes with time to hydrochloric acid, which readily reacts with propylene oxide or butylene oxide and therefore is removed from the solution. Chromate-based inhibitors give the mixture a characteristic yellow color. Other possibilities include polyphosphates, silicates, borates, and various antioxidants.

Sequestrants and chelating agents are used to "disarm" metal ions present in the solution, which could otherwise reduce the efficiency of other components, and assist with cleaning stains, which often contain metal compounds. The most common sequestrants used in paint strippers are EDTA, tributyl phosphate, and sodium phosphate.

Colorants may be added.

Alternatives

Heat guns are an alternative to chemical paint strippers. When heated, softened paint clumps and is easier to contain. High-temperature heat guns at 1,100 °F (590 °C) or more create toxic lead fumes in lead-based paint, but low-temperature heat guns and 400 °F (200 °C) infrared paint removers do not create lead fumes. Fire is a possible hazard of using heat guns.

Steam can be used on large surfaces or items to be stripped, such as window sash, can be placed inside a steam box.

Safety

A product's material safety data sheet can provides more safety information than its product labels.

Many traditional paint strippers were or are based on dichloromethane, which can pose serious health risks. It is likely a carcinogen, and is banned in some countries for consumer use. Despite this, deaths from dichloromethane are extremely rare at fewer than 2.4 cases per year and associated mostly with users applying large amounts in confined, poorly ventilated spaces. When applied in reasonable amounts and with typical levels of ventilation, or outdoors, it is generally safe to use.

Removing old lead-based paint can disperse lead and cause lead poisoning, leading several US workplace and environmental regulations address removal of old paint that could contain lead.

See also

• Distressing
• Nitromors

External links

• JAIC 1993: The composition of proprietary paint strippers
• Old-House Journal article on paint removers starts on page 58
• "Urban Expression", a paper on the history of NYC graffiti.
• "How To Use Paint Stripper", an explanation on usage of paint strippers
• Remove Old Paint from Walls