Chemist at work
Generally a typical house paint is made up of three basic components: the Binder, the Pigment & the Solvent.
Pigments are made up of minutely sized particles, which can remain suspended in a liquid base for upon mixing for extend periods of time. The pigment usually, considered as the color component of the paint also gives the paint it's coverage properties and its ability to provide ultra violet protection.
A liquid resin called the binder This binder is like a glue which holds everything in the paint (including the pigments) together giving the paint its ability to bond, and endure the elements.
A liquid called the solvent is used in combination with the pigment and the binder to provide the proper consistency the paint. A solvent is basically a thinning agent. Sometimes the solvent combined with the resin considered as only one component of the paint
Most modern paint will contain compounds or other substances that add particular properties to the paint such as plasticizer and drying accelerators.
The first latex paints consisted of natural latex as a resin. The resin in latex today may be an acrylic or some type of synthetic substance. If you have ever been concerned about latex allergies you shouldn’t have to worry about the modern day latex paints.
The solvent of latex may consist of mostly water with additives to help the paint components coalesce. The pigments used in latex are often made of the same materials used in alkyd or oil based. Other additives may be used provide special characteristics to the paint.
There have been so many developments in this industry that we could not make attempt to specify what technically qualifies as a modern latex paint. Paint having practical characteristics of latex paint are usually labeled as latex , but sometimes the manufacturer feels it is better to just categorize the paint without the term latex on the label. These paints and stains will usually carry the terms acrylic or waterborne in there description.
Natural oil based paints were very common decades ago but have since been being replaced by alkyd paints. The resins of oil based paints were commonly natural products such as linseed oil or Tung oil. The solvent would probably consist of mainly turpentine.
Alkyd paints consist of a synthetic type of resin called “alkyd” and probably mineral spirits as a solvent. The alkyd paint is generally recommended for more types of surfaces than the natural oil based paints were.
You can still find paints today labeled as oil based, but they may consist of other alkyd type ingredients combined with the linseed oil to give the paint alkyd like qualities.
As with most materials today so many recent developments have taken place in the paint products industry that we will leave any categorizing between oil and alkyd or what ever else up to the manufacturers.
Although it may be technically incorrect, many house painters still refer to any water soluble paint as latex and any alkyd paint as oil based, regardless of the labels on the can and eventually any paint store sales person in a will realize this. By no means does this imply that the painter does not know there’s a difference, some of these guys/gals even have there favorite products in different categories, but for daily practical purposes, many house painters and others have chosen to place most of there house paint products into the oil or latex category.
It’s not that one type of paint is better than another, but that the paint is better for what is meant to be used for. There are some people from the old school that believe that oil based is good latex is not as good and they try to by only oil based products for there painting needs.
With all the products available today most are designed for a certain purposes. As alkyd products are NOT generally recommended for direct contact with masonry products, a few oil based type products are designed for such purposes. Alkyd products bond quite well to most surfaces at first, however in some cases they may lose their initial bond over time. Example: Alkyd usually bonds well to latex paint, but if it is used over latexes on surfaces such as wood that expands and contracts very much, the alkyd will not flex as much as the subsequent latex coat leading to top coat problems.
On the other hand latex primers are sometimes recommended as go between barriers of a substrate and alkyd finish where it is desired to have an alkyd finish over a surface not suitable for direct contact with alkyd paint
Alkyd primer sealers are often used over latex paint such as in a case where a ceiling is discolored or stained to the point that it needs a very capable sealer, this does not usually create a compatibility problem.
Alkyd primer will bond to wall board, but it will usually raise a nap on the wallboard much more than latex primers do, creating rough surface that will require vigorous sanding in order to be ready for the finish coat.
Latex paints are generally quite versatile, they will bond to wood, wallboard, plaster, aluminum, clean galvanized metal, masonry, and many plastics.
Latex are generally NOT recommended for direct contact with ferrous metals as these type of metals can rust. If used directly over bare wood, latex paints have a tendency to raise the grain of the wood, for this reason alkyd is often recommended as an interior wood primer.
Latex paints generally do not have a good reputation for bonding well to glossy alkyd/oil finishes but will bond very sufficiently to alkyd primer or alkyd flat paints. A solution for going all latex over gloss finishes may to use a bonding primer. Bonding primers are available in latex, in fact some of the latex primer sealers will function as a good bonding primer.
Latex are generally more transparent to moisture than alkyds allowing water vapor to pass through. This property of allowing moisture to escape through the paint can help prevent pealing from exterior wood surfaces as where a moisture resistant coating may blister as moisture passes through to the exterior.
It is sometimes desirable to use a paint as a vapor barrier. This may be to prevent moisture from passing from the interior of a house into the exterior walls. Most houses are built with a vapor in place. But if it is decided that an existing house needs more of a vapor barrier than it already has , the walls can be painted with a moisture resistant alkyd or moisture resistant latex.
Also See Choosing The Right Paint