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Latex Paint vs Oil Based Paint

(© Copyright 2011 Shawn Cole. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)






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

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 elastic.

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 painted.

Disadvantages of Latex Paint

Refer to the chart at the end of the article for a more complete list of advantages and disadvantages of latex paint. 

The main disadvantages of latex paint:

Advantages of Latex Paint

What Does the Term "Acrylic Mean?

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 Based 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.

What Does the Term "Alkyd " mean?

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.

Advantages to Oil Based Paint

Disadvantages of Oil Based Paint

Refer to the chart at the end of the article for a more compact list of advantages and disadvantages of oil-based paint.

Difference in Drying Between Oil and Latex Paint

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 elasticity.

How to 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.

Test the Paint to Determine if it 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.

Prepare the Wall If It Has Oil-Based Paint in Order to Paint Over it With Latex Paint

Why 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 latex paint.

The Peeling of Oil Based Paint May Not be the Failure of the Paint

The 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 results.

Quick Look At  The Differences Between Latex and Ol Based Paint


LATEX PAINT
ADVANTAGES
DISADVANTAGES
Easier to apply than oil based paint because it is thinner and spreads easier
Adheres poorly to dirty or chalky walls
Easier to clean up than oil based paint
Shrinks more than oil based paint
Quicker drying time
Can cause surface stess on the previous paint
Fade resistance
More sensitived to temperature changes
Mildew resistance
May stain  before it is fully cured
Non-combustible
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 paint



OIL BASED PAINT
ADVANTAGES
DISADVANTAGES
Preferred in harsher environments with large temperature swings
Requires more care to achieve a smooth coat
Recommended when painting dirty, chalky surfaces
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 latex

Requries a paint primer

Oil based paints have a glossy finish whereas latex paints are available in both glossy and matt finish.