Introduction

Chemical paint strippers are available as liquids, gels or pastes that use strong chemicals to loosen the paint from the surface, in order that it may be scraped off with a knife or wire wool. There are two key types of chemical stripper, Solvent based or Caustic Alkali based, both of which should be handled with extreme care.

Chemical strippers are excellent at removing paint from moulded and contoured surfaces, the choice of which one to use is down to the size of the area to be stripped, the type and thickness of paint to be removed and the amount of ventillation available.

• Bear in mind almost all paint strippers exaggerate the speed at which paint is removed

Solvent based strippers

These work by breaking bonds between the wood and the paint. They are usually flammable and volatile. To reduce evaporation, manufacturers usually add wax to the stripper and this must be washed off to ensure that paint can adhere to the surface.

• Removes paint from contoured surfaces
• Safe to use on glass panes
• Suitable for lead paint

• Costly to remove thick layers of paint
• May require several applications
• Use is often hazardous

DCM strippers

Methylene Chloride or Dichloromethane (DCM) is most widely used in paint strippers, also available in a non-flammable version. DCM can remove almost any kind of paint as it has a small molecular structure which is able to penetrate through the layers of paint to break its bonds with the wood. Thereafter, as it tries to evaporate, it causes the paint to wrinkle away from the surface which makes its removal with a knife easy. However, being very volatile, it evaporates away quickly which means thick or multiple layers of paint will require several coats of DCM to be removed.

• This chemical is considered to be potentially carcinogenic, and it can cause dizziness, headaches and poor coordination if inhaled, leading to kidney and liver damage after prolonged exposure.

Solvent thinners

Acetone, Toluene & Methanol are used in a potent mixture of all three chemicals to strip paint from its substrate in the same way as DCM works. This is the cheapest form of stripper being essentially just a paint thinner, so it is slow to work on most paint types. All three ingredients are highly flammable and inhalation can cause drowsiness, dizziness and headache.

NMP strippers

N-methylpyrrolidone (NMP) has been used in paint strippers since the 90s, but was applied in an industrial context prior to that. It too breaks the bond between paint and substrate, but being a much larger molecule than DCM, it takes much longer for this solvent to work. That said, it does not evaporate as quickly and therefore does not require multiple applications.

On the downside, NMP will not remove baked-on or polyester coatings and it is also relatively expensive.

DBE strippers

Dibasic Esters (DBE) are a combination of dimethyl esters of adipic, glutamic and succinic acids which are biodegradable and suitable for incorporation into a water-based paint stripper.

Developed by DuPont, the same people who brought us Lycra, this stripper is not volatile so requires less precautions for ventilation. It does not need to be reapplied and paint can be washed off with a jet of hot water.

They are not terribly effective strippers, however, so will require a long time to remove the paint.

• Water-based products can cause damage to wood and veneers.

Caustic alkali based strippers

Paint strippers based on caustic alkalis eat away at the layers of paint by breaking down its molecules. This loosens it from the substrate such that it can be removed with a putty knife. They are non-flammable, but they are extremely hazardous.

• Highly effective
• Cheap
• Well suited to painted masonry

• Highly hazardous
• May damage substrate

The most common caustic alkali is lye or sodium hydroxide (caustic soda), which is often mixed with trisodium phosphate (TSP).

This is the cheapest and most effective form of paint stripper, but it can often damage a wood substrate by discolouring it and making the cellulose fibres swell. It can also react with an aluminium door.

It is well suited to removing paint from cement and masonry, however it is usually the case that the surface treated with alkali strippers will need to be neutralised with a mild acid to stop the reaction continuing.

Lye is available in powder form to be mixed with water. When adding water, the mixture must be made in a steel container; do not use plastic, glass or aluminium as these react with the sodium hydroxide. When lye and water mix, their chemical reaction produces a lot of heat, so the lye should be added to the water, not the other way round to avoid the water boiling over, and you should not hold the container as it will heat up.

• Even the briefest contact with lye will severely burn skin and eyes, so protective clothing and goggles are vital.

Further information and useful links

• Guide to paint
• More painting & decorating topics

• Find a Paint Stripping Service near you
• Find a Paint Materials store near you