|
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.
|
