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 Stripping 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.