The
Pros and Cons of
Latex over Oil-Based Paint
What Works Best Under What Conditions in the NW
By Paulette Rossi
Both interior
and exterior architectural coatings fall into two general categories:
latex or water-based paint or oil-or alkyd-based paint.
Contractors and
do-it-yourselfer’s select latex for its good performance and
ease of use. Latex moved from 30% to 35% of paint sales in the 1970’s
to over 80% of architectural coatings sold today.
While the pigments
in latex and oil-based paints are often the same, different carriers
and binders give latex and oil-based paints different characteristics.
The vehicle or carrier is the volatile part of the paint that evaporates
as the paint dries. The carrier in latex paints can be water with
some solvent — typically glycols and glycol ethers are used as
coalescing agents. In oil- based paint organic solvents usually from
petro-chemicals are used with mineral spirits being prevalent.
The carrier keeps
the pigments and the binders in suspension until the paint is applied
to a surface. The binder is the body of the paint, the permanent part
of the paint that remains when the paint dries. As the name implies,
binders help the paint to adhere to a surface.
In oil-based paint,
binders can be synthetic resins, derived from petroleum, including
alkyds, polyurethanes, and silicones. Natural oils include linseed,
soybean, safflower, tung, and cottonseed oils.
Water-soluble
binders include acrylic resins, polyvinyl acetate, and styrene butadiene.
The best latex paints are 100% acrylic, followed by vinyl acrylics
and polyvinyl acetates.
In oil and latex
paints titanium dioxide is the primary pigment used for its hiding
properties. Pigment extenders include: silica, calcium carbonate,
dolomite, talc, clay, mica, barite, and gypsum. Pigment extenders
minimize the settling of the paint solids and impart gloss. Extender
pigments are also bulking agents that influence scrub, stain and chalking
resistance. Paints other than white also contain color pigments.
Most people buy
latex paint because painting projects using latex omit less odor and
cleanup with soap and water, but latex has many other positive characteristics.
In the damp Pacific Northwest, latex is preferred because it can be
painted over a damp surface. Oil is a non-breathable surface sealer
while latex breathes allowing moisture to escape. The peeling and
cracking that occurs when moisture is trying to escape from a surface
coated with oil-based paint is eliminated with latex paint.
Latex paint, especially
acrylic latex, is less prone to fading or yellowing than oil-based
paint. Chalking is a characteristic of oil-based paint. This self-cleaning
process causes oil-based paint to lose much of its color intensity.
Even after oil-based
paint is dry to the touch it continues to dry until the paint starts
to crystallize and crack. Latex paint remains flexible. Because latex
paint is not as sensitive to alkali as oil-based paint it can be used
over cement and plaster.
Oil-based paint
can be applied at a lower temperature than latex’s 50-degree
Fahrenheit minimum temperature but oil-based paint will never dry
in high humidity. Latex paint is dry to the touch in minutes and ready
for a second coat in about four hours. Oil-based paints are dry to
the touch in six to eight hours but need twenty-four hours before
re-coating. The longer the drying time the greater the chance of insects
and dust penetrating the wet surface.
Latex paint is
also easier to apply as it flows off of the brush or roller. Oil-based
paint is sticky and must be stretched out and worked into the surface.
The chief advantage of using oil-based paint over latex is that the
oil-based paint requires less surface preparation and adheres to dirtier,
shinier, or more weathered surfaces than latex paint. It is more resistant
to abrasion.
Containing anywhere
from 50% to 90% water, the environmental impact from water-based paint
is much less than oil-based paint. Jim Quinn, supervisor of Metro
Regional Government’s household hazardous waste program notes,
“Oil-based paint is considered hazardous waste under State and
Federal regulations. It costs Metro over $7 a gallon to bulk and dispose
of the oil-based paints left-over from household applications.”
Household leftover oil-based paint is sent to a cement kiln in the
Midwest for energy recovery.
Because latex
paint formulations are compatible Metro can reblend the useable latex
paint it receives from households and some business. Selling this
paint back to the public at cost covers production expenses. Re-using
the resources preserves habitat, prevents pollution, and conserves
energy, water, and landfill space.
Since 1992 Metro
has produced over a half million gallons of reblended latex paint
suitable for interior or exterior application. Filtered to industry
standards the paint has been brushed, rolled, and sprayed on wood,
masonry, concrete and vinyl and metal siding. Tested for performance
and environmental considerations the latex is available in 13 colors.
Call Metro Recycling Information at 503-234-3000 for a color brochure
and money-saving coupon. Or consult Metro’s website www.metro-region.org/paint
for a color chart and test results.
Paulette Rossi
is a Certified Master Recycler promoting the use of Metro Recycled
Paint available in a rainbow of colors. She can be reached at: rossip@metro.dst.or.us
or 503-797-1827. |
