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Understanding Common Paint and Finish Strippers



This article will discuss the various chemicals and chemical combinations used in modern paint and varnish removers. It should be noted that this information is presented as a general guide and should not be used in place of the manufacturer's recommendations. You should always read the directions provided by the manufacturer and take care to ensure all safety precautions are followed.

There are many strippers and paint removers available at the local hardware store. This guide is designed to help sort out some of the more common ingredients. Paint and finish stripper manufacturers are required to list their ingredients on the package, making it somewhat easier to understand the product you are purchasing. In addition to the chemicals and solvents discussed below, there are a number of other "professional" stripping chemicals that should only be used by an experienced professional with the proper safety training and equipment.

Understanding Striping Solvents and Chemicals There are only a few commonly used chemicals in modern wood strippers. These solvents and chemicals are sometimes used alone or in varying combinations and strengths. They are commonly listed by the following acronyms:

Solvents:
MC = Methylene Chloride
ATM = Acetone, Toluene, and Methanol
NMP = N-Methyl Pyrrolidone
DBE = di-basic esters

Alkalis:
Lye = Sodium Hydroxide
Ammonia = Ammonia Hydroxide

Recommendations

MC = Methylene Chloride
Methylene Chloride is one of the oldest and most common solvents used in paint and varnish strippers. Although MC is non-flammable it is also toxic and a suspected carcinogen. It metabolizes in the blood to form carbon monoxide. This causes the heart to pump harder and can trigger heart attacks in people with existing heart conditions. For this reason, if you have a heart condition, avoid using a paint remover with MC as a listed ingredient.

MC based strippers are available in different strengths and consistencies. Liquid and semi-paste are the most common consistencies. The semi-paste stripper is often used for vertical objects where the stripper needs to cling to the paint. The solvents in these strippers evaporate very quickly so paraffin wax is added to help slow evaporation. The wax will rise to the surface and help form a protective skin. Disturbing the wax skin will cause solvents to escape and weaken the stripper.

Alkali fortified MC is often used in "marine grade" finish removers and are available at most marine supply store. Alkali fortified MC strippers are effective on tougher coatings such as epoxy and polyester. They are more expensive and hazardous to work with so additional care should be taken when selecting and using these stripping agents.

Note: The waxes used in MC based strippers must be removed from the wood before refinishing. Failure to thoroughly remove the wax may cause interference with the new finish. A clean cloth and solvent such as naphtha, lacquer thinner, or alcohol should be used to remove the wax residue left behind when the stripper is removed.

ATM = Acetone, Toluene, and Methanol
These are the three primary ingredients in Lacquer Thinner and are used together to form a very aggressive stripping agent. ATM strippers are available with wax and thickeners to form semi-paste finishes as well as in forms without any of these additives.

ATM Strippers works very well on most old finishes and paints. The chemicals in ATM strippers evaporate very quickly so wax is added to keep them in contact with the paint or finishes long enough to allow them to penetrate and soften the surface. The primary advantage of an ATM stripper is that they are inexpensive and do not have the health concerns of Methylene Chloride. They are flammable and air polluting. Some brands may contain a alkali that will stain some hardwoods.

ATM Refinishers are also available. These products don't contain the wax and thickeners of the ATM Strippers. Because the solvents tend to evaporate quickly the manufacturers recommend you use manual scraping methods with the refinisher. Most people become frustrated with the slow rate of finish removal from ATM Refinishers. Because of this slow rate of removal, and the fact that ATM Refinishers are simply over priced lacquer thinner, we recommend you avoid "ATM Refinishers" and use an "ATM Stripper" instead.

Note: The waxes used in ATM based strippers must be removed from the wood before refinishing. Failure to thoroughly remove the wax may cause interference with the new finish. A clean cloth and solvent such as naphtha, lacquer thinner, or alcohol should be used to remove the wax residue left behind when the stripper is removed.

NMP = N-Methyl Pyrrolidone
These finishes are not as effective as strippers based on MC and often work at 1/3 to 1/2 the speed. They are also not effective on epoxy, Polyester, or baked on coatings. The solvents in NMP evaporate slowly making wax coatings and additives unnecessary. The slow evaporation also makes NMP less toxic to work with as well as less flammable and less air polluting. The chemicals in NMP are expensive and NMP based strippers are likewise expensive.

DBE = di-basic esters
DBE is less effective than the other three strippers described above. Overnight contact is often required to affect the finish and NMP is ineffective on Lacquer and Shellac. It has a very slow evaporation rate making it relatively safe to use and eliminating the need for a wax additive. Some DBE based strippers use water to thin the DBE. The water can cause some problems with old veneers, iron fasteners, and thin wood panels. These strippers should be avoided if you think the water will affect the furniture.

NMP/DBE Combination Strippers
A couple of manufacturers have combined the last two solvents into one stripper. The DBE helps to reduce the price of the stripper. Other chemicals are sometimes added to replace the potentially damaging water. The speed of finish removal is still slower that with a MC or ATM based stripper and falls somewhere between NMP and DBE for finish removal. NMP/DBE combination strippers are generally less toxic although some manufacturers will add solvents such as xylene, which make them toxic, air polluting, and flammable.

Alkali Fortifiers

Lye = Sodium Hydroxide
Lye is one of the oldest chemical strippers. It works well but is dangerous to work with and damages the wood. The lye can dissolve glue and causes the woods surface to become soft. It should generally be avoided but can be used sparingly to remove stubborn paint from the wood's pores and to remove finishes from metal hardware (except aluminum). Lye is also effective on old-fashioned milk paint. Another good use for lye, because of its low cost, is removal of paint from large outdoor surfaces such as fences and outdoors siding. It is usually supplied in powdered form and mixed with warm water. Lye can usually be purchased from most paint stores. It is very important to neutralize the lye with a 50/50 solution of water and vinegar to neutralize the lye. It is also very aggressive and cause chemical burns if it comes into contact with your skin. Proper safety procedures should be taken and the manufacturers directions should be followed carefully.

Ammonia = Ammonia Hydroxide
Ammonia Hydroxide is often used to fortify solvents and increase their strength. The one downside to using a stripper with ammonia is that it may tend to darken some hardwoods such as oak, mahogany, cherry and walnut.

Which stripper should I use?
The most aggressive strippers are Methylene Chloride (MC) based. However these strippers should not be used by people with heart conditions or health concerns. If you don't know what type of paint or finish you are removing a Methylene Chloride based finisher is the best bet for effective removal.

Polyurethane Finish - Methylene Chloride and methanol
Most old paints and finishes - Methylene Chloride and methanol reduced with acetone and/or toluene
Epoxy and Polyurethane - Alkali-fortified Methylene Chloride

If you are concerned about the health effects of Methylene Chloride, an ATM based stripper is the next best bet. Although not as strong as a MC based stripper, ATM strippers will remove many paint and finishes.

If your primary concern is expose to toxic solvents NMP or NMB/DBA strippers are the next best choice. They tend to be a little more expensive that MC or ATM finishes because of the chemicals used in their production.
 

 

 

 

Your Hosts,

Rod & Jen Keyser

Owners of The Restoration Studio LLC

 

“Our goal at The Furniture Refinishing Studio Learning Center is to help empower you to step beyond the realm of ordinary, and assist you so that your furniture restoration projects become extraordinary. We are passionate about furniture,and we understand the importance it plays in everyday life.”

Rod & Jen Keyser The Restoration Studio LLC