2011 Shawn Cole. All Rights Reserved. This material may
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Please read the article "Understanding Paint Quality" about paint to
obtain a good background of information about what makes up different
types of paint to understand the actual components of paint such as
pigments, binders, a filler called the "vehicle" and the
different additives in paint. The subjects covered in that
article are only referenced in this article.
There are basically two (2) types of paint on the market. Acrylic
latex paint and oil-based paint also known as "alkyd" paint.
Acrylic latex paint is made with water and an acrylic resin
binder. Oil-based paint uses a hydrocarbon-0based solvent as the
vehicle and an alkyd resin.
The pigments in both oil based and latex paint determines the degree of
coverage and the color the the finish. The more pigment, the
better hiding properties of the paint. The most important pigment
is titanium dioxide, while other important inorganic pigments include
carbon black and iron oxide. Most paints do not use titanium
dioxide because it is very costly but it provides a high quality
paint. Most paint manufacturers substitute clay and silica
as pigments because they are less costly but do not hold up as
well. Manufacturers add fillers to their paint products to
enhance the performance of the paints. This is why it is
important to read the label of the paint cans and answers the vexing
question of why some paints cost $12 per gallon and some cost $45
dollars per gallon.
Both oil based and latex paints use binders to solidify the paint into
a film. Typical binders include synthetic or natural resins such
as acrylics, polyurethanes, polyesters, melamines, for
latex. Linseed oil, tung oil or alkyd resins are the primary
binders for oil-based paints. 100% acrylic or vinyl are binders
for water based paint like latex or acrylic.
Latex paint was invented in the 1940's in Canada, using the resin from
a rubber tree as a binder. The general name for this original
binder is called "latex". Even though manufacturers don't use the
rubber tree resins any more the name stuck. The binders are now
made from synthetic (man-made) resins of polyvinyl acetate and styrene
butadiene and other synthetic binders.
All paints are composed of a solid, binders and pigments and a vehicle
such as water for latex paint. The binder's function is to
actually bind the pigments and the vehicle together. The solid
part of the paint is heavier than the vehicle and that is why paint
needs to be stirred or "shook-up" at the store on a machine to mix the
heavier parts of the paint throughout the vehicle (water).
The highest quality of latex paint will advertise that it is 100%
acrylic latex. These paints are the most expensive,
top-of-the-line paint from the numerous manufacturers. You
will also find styrene, epoxy and polyvinyl acetate listed on paint
cans which are used as resins. Latex paint using vinyl acrylic is
the most popular paint ingredient.
If the paint can is advertised as "100% acrylic latex paint", the
manufacturer used a synthetic polymer or plastic as the binder.
Latex paint uses only one binder, called an elastomer, which means that
the latex paint actually hasa a surface that is not rock hard, but is
After latex paint is applied to a wall, it remains flexible, meaning
that as the temperature changes the surface will expand or
contract. Latex paint is also porous and allows moisture to
escape from the paint surface.
Thirty years ago, the manufacturing processes were not as good as they
are with today's latex paint. The latex paint manufactured
today is as good as an oil based paint and in many ways is superior to
the oil based paint. The surface of of today's latex paint
is extremely durable and resists scuffs and scratches, washability,
breathability and provides superior adhesion to the surface to be
Refer to the chart at the end of the
article for a more complete list of advantages and disadvantages of
The main disadvantages of latex paint:
- Not suitable for painting over steel without first using a primer.
- If the surface is bare wod, latex paint will raise the grain of
the wood unless that bare wood is first painted with a primer.
- Does not adhere to dirty or chalky walls well
- Shrinks more than oil based paint
- More sensitive to temperatur changes
- May stain when contaminated with a water-soluble mixture
- Has a softer film (the outer coating of the paint)
- Takes longer to cure than olil based paint and can be damaged
easily until thoroughly cured
- Latex paints do not cause cracking and peeling as do oil based
- The surface of the paint actually "breathes" -- meaning any
moisture in the drywall can escape through the porous surface of the
- Latex paint does not have the strong odor of an oil based paint
-- that means less VOCs (volatile organic compounds) to harm the
- Latex paint can be easily washed with soap and water from
brushes, rollers and drips
- Latex paint is not flammable
This is a manufacturing term that means
a synthetic latex. Most latex paints on the market today no
longer use the resin from the rubber trees as a binder. Pure
acrylic (water based) paints are usually a better quality than regular
water-based latex paints. They are usually more expensive, as
well. Be sure to read the label before buying a latex paint to
determine if it is pure 100% acrylic or a latex type paint.
Oil paint was originally made with linseed oil as a binder. That
is why the name "oil based" paint was originally coined and still in
use today. To thin the paint you need mineral spirits or
turpentine to dilute the paint. Many years ago, oil based
paints were the choice of all painters but with the improvements in the
latex paints, and the restrictions in several states against using oil
based paints, latex is favored by most painters.
The paint thinner needed to clean spills and brushes needs to be
disposed of in an appropriate manner. In some states, you need to
dispose of the partly empty thinners at a special location since they
cannot be simply put in the garbage with the other trash.
The main reason for the use of oil based paint is the hard, durable
finish that resists scratches and abrasions. This finish is so
hard that it cannot be painted directly over latex paint because the
latex paint surface has a flexible surface which will cause the oil
based paint to crack and flake as the temperature changes causing the
latex paint to expand and contract. The same is true with
painting oil based paint over a latex paint. The latex paint will
flex and expand with temperature and the solid surface of the oil paint
over it will lose its adhesion.
The same problem can occur when you repeatedly paint layer after layer
of oil based paint over oil based paint. The surface is so hard
that the suhbsequent layers tend to stop adhering well and will
actually crack. While in most private home situations, this will never
be encountered, paint on the interior walls of an apartment will
be painted much more than a private home and thus will create many
layers of paint build-up.
Solvents give the oil-based paint the proper consistency. They
are used to keep the ingredients in liquid form and act as a "carrier"
for the binders and pigments. Oil-based paints use thinners
(petrochemical distillate as the solvent. That is why oil based
paints are flammable and toxic. Latex paints use water as
the primary vehicle which makes them much less hazardous.
Alkyd is the manufacturing term meaning
a synthetic resin. In other words, it is a made-made oil and is
not derived from plants or petroleum.
- Alkyd paint goes on smoother but has a much longer drying time as
this paint needs to dry over a longer time period of up to 3 days.
- The alkyd paint has a very hard surface that resists scuffs.
- Oil based enamels provide a smoother finish than latex paints.
- Oil enamels are easy to wash because the surface is much hard
than latex paint.
- Oil paints are more chemically resistant to stand up to washing
detergents than latex.
- Since oil based paints are thicker than latex, they tend to hide
wall imperfections edtter than latex.
- Oil based paint offers a less clear refractive index compared to
latex paint because the linseed oil contains smaller molecules than
latex paint does. Thus the paint film provides a feeling of more
depth and warmth than latex paint.
- When running your hand over an oil paint on a wall, the texture
will feel smoother than a latex paint (which almost always has a
Refer to the chart at the end of the
article for a more compact list of advantages and disadvantages of
-- if you paint your interior trim with oil, you will hae to
touch it up more often.
-- If you are painting your walls or trim with a white
colored oil based paint, the white has a tendency to turn yellow after
-- Oil based paint does not resist mildew that may form in a
high-moisture room such as the bathroom.
-- States are starting to pass laws against using
oil-based paint. The reason is that the oil-based paint gives off
gasses of volatile organic compounds (VOCs). Most paint that is
on the wall prior to 2005 used solvents, oils and dryers that no longer
comply with some new rules. As regulations become more strict, it
might not be a good idea to continue using a paint that may be
restricted in the future.
-- Alkyk oil paint also has a long-lasting odor, so
ventilation is mandatory when using them
- Oil based paint tends to bubble during the paint
process whereas the latex paints do not bubble Because of this,
it is imperative that each coat is allowed to "cure" for several daysa
before applying a second coat.
-- Oil based paint does not breath as does latex
paint. As a result, if the surface of the underlying wood
or plaster has any moisture, the oil based paint will tend to
peel. This happens because oil paints form a tigher, non-porous
film which doesn't allow moisture vapor to pass through it
and results in a pressure build-up that breaks the paint bond and
delaminates the paint causing peeling.
Time -- Oil based paint needs at least 24 hours to dry between
coats under best conditions and up tos everal days if there is any
humidity in the air.
The main difference in drying is that latex paint forma a flexible film
as water evaporates and the once-floating pigments move closer to
gether as the binder does its job. Oil based paint forms a tough
plastic film as the binder reacts with oxygen in the air. The oil
paint will adhere better to problem surfaces because the oils are small
and seep into the pores of the wood or even into the pores and cracks
of the previous paint. Latex does not seep into any pores or
cracks. It allows the moisture vapor to seep through its surface.
Latex and oil paints do not cure in the same way. Oil based paint
never stops curing. As it ages, it continues to oxidize
becoming more and more brittle and prone to cracking and peeling.
Latex cures in about two (2) weeks and stays pliable and rubbery with a
surface that actually breaths and allows moisture in the drywall or
wood underneath it to evaporate. The surface contract or expands
with temperature differences, while oil-based paint surfaces have no
Paint Latex Paint Over Oil Based Paint
Most people have heard the story that it is impossible to use latex
paint over oil-based paint. While this is truei f you simply open
a can of latex paint and start painting over the oil-based paint, there
is a process which will ensure that you really can use latex paint over
an oil based paint. Most homes built before 1950 have layers of
oil-based paint on the walls.
is Latex or Oil-Based Paint
If you are not sure if the wall was
painted with latex paint or oil based paint, simply take a cotton ball
soaked in rubbing alcohol or use nail polish remover that contains
acetone or lacquer thinner. Rub the wall with a cotton ball.
If the paint comes off onto the cotton ball, the paint is
a latex paint. If the paint is unaffected, it is an oil-based
Paint in Order to Paint Over it With Latex
- If the original paint on the wall is an oil based paint, you need
to prepare the wall to partially removed the hard, smooth surface to
give the latex paint some adhesion since oil-based paint has a very
smooth surface. Simply lightly sand (by hand -- not machine) with
a 100 grit piece of sant paper wrapped over a piece of wood. You
are not removing the paint, simply roughing up the surface to change
the smooth oil surface into a surface that provides "teeth" or "bite"
(irregular, non-smooth surface) for the latex paint to adhere.
- Wash the walls with TSP to remove all the dust, dirt and grease
and loose paint and dust from the sanding procedure.
- Apply a coat of primer to the wall
- After the primer is allowed to dry for several days, apply the
latex paint. You will need to apply two (2) coats of the latex
paint of your choice for good coverage.
Paint Latex Paint Over Oil Paint Soemtimes Fails
As you have already learned, latex paint has a pliable, porous surface
that actually expands and contracts with temperature while oil based
paint has a hard, unmovable surface. Most buildings older than
the 1950's have been painted with multiple layers of oil based
paint. When a flexible layer of latex paint bonds directly
on top of a hard, brittle oil paint that has not been sanded to have
its surface roughed up, and a good primer applied, the movement
of the latex paint as the sun heats the surface expands and pulls on
the non-movable oil-based paint. This causes the oil based paint
to lose its adherence to the main wood or plaster surface by applying
pressure on the unmovable oil paint surface. This is much
more common when using latex paint over oil paint on the outside
of the building than it is on interior walls which are not subject to
extreme temperature changes.
Using a 100 grit sand paper causes the smooth oil surface to break up
and allows for expansion by literally breaking up the solid smooth hard
surface. This allows the latex paint to float ovedr the small
microscopie ridges and thus relieve the pressure on the oil paint
underneath the latex paint. As stated above, latex paint does not
flor into tiny crevices as oil based paint does but lays on the surface.
Even with all precautions, all oil based paints will peel at some
time. It is the nature of oil based paints. Oil based
paints continue to oxidize and get brittle over time which
eventually causes peeling. On the bright side, the peeling
process can be a very long process. Scraping the peeled paint,
primering the wood and repainting with latex and hope that it will be
years until you have to do that again is the most common procedure
by homeowners. It is actually very rare that the old
oil based paint will peel so badly with latex on it if you sand the
surface to break up the smoothness to allow for the paint to actually
expand and contract into the ridges caused by the sandpaper, properly
clean the surface and apply a good primer before the final top coat of
Not be the Failure of the Paint
- If the peeling of the paint is around windows, you may need to
take off the trim boards and seal up the gaps around the frame that are
causing moisture from inside the structure to leech through to the
paint causing the paint to lose its adherence / bond to the wood
- If the paint only peels on the outside wall of the athroom, you
have a moisture vapor seeping through your wall that is pulled through
the wood when the sunshine warms the wall. Either remove the dry
wall and put in a plastic moiasture barrier or install a ventilation
fan to get rid of the moisture created by your shower or tub. If
this is the problem, then even latex paint will peel because it will
lose its bond
New Oil Based Paint is Not the Same As it Was
Manufacturers no longer make the oil based paint as thick as they did
30 years ago. Many manufacturers hage changed their formulas to
meet the clean-air rules. Manufacturers can still sell oil-based
paint with a high solvent content by simply re-labeling it to
"quick-dry enamel", industrial maintenance coating" or "marine
paint". The problem is that you cannot buy this in gallons so the
cost is much higher. Nevertheless, the new oil-based paint has
imrpvoed so much over th eolder paint formulas, that painting with an
oil based paint that is not as "thick" will still provide excellent
Look At The Differences Between Latex and Ol Based Paint
|Easier to apply than oil based
paint because it is thinner and spreads easier
|Adheres poorly to dirty or
|Easier to clean up than oil
|Shrinks more than oil based paint
|Quicker drying time
|Can cause surface stess on the
|More sensitived to temperature
|May stain before it is
|Lates takes longer to cure than
oil based paint
|Retains the color much better
than oil paint
|Exposing latex paint to high
humidity such as in the bathroom, will not hold up as well as oil based
paint. (Many paints have additives to prevednt this problem).
|Latex does not chalk as will oil
|Preferred in harsher
environments with large temperature swings
|Requires more care to achieve a
|Recommended when painting dirty,
|Paint dropped on floor or other
unintended areas hard to clean up
|Less susceptible to staining and
abrasions in high traffic areas
|Increased brittleness and
yellowing as it ages
|Covers imperfections in teh wall
surface better than latex
|Some states are passing laws
against oil based paint
|Oil based paint is thicker and
thus harder to apply and covers less square feet of wall space than
|Requries a paint primer
|Oil based paints have a glossy
finish whereas latex paints are available in both glossy and matt