The earliest known use of paint dates back some 30,000 years to the days of early humans drawing murals on cave walls, and what followed was millennia of artistic styles involving paint. Despite this long history of painting, it was not until 1700 that the first paint mill was established to mass produce this medium of decorating. By the end of the 19th century, paint factories were thriving all over the world, but the big game change came in the 1950s when middle class Americans started to paint their houses and did not like the messy oil based paints that predominated the market so they clamored for a relatively new invention: latex paint.
Before the invention of modern latex paint, water based paints were water soluble which meant it not only got diluted when it was wet, it also dissolved in water when it was dry. For example, orange juice is water soluble and remains water soluble after it dries which allows you to wash dishes, counters and floors. If you remember your Mark Twain, you would be familiar with the expression ‘ whitewash’ which today has become synonymous with hiding the truth. It is in reference to the earlier forms of water soluble paint; you had to repaint your fences on a regular basis because the white wash would flake away. Consequently, at the time, oil-based paint was most common because it was not water soluble. Once it dried it was there to stay. With the invention of latex, however, paint became water-thinnable which means it thins with water when wet, but once it dries it is insoluble – it can be washed after it dries but it won’t dissolve. This meant painting was easier and cleaner to apply, and less harmful to the environment.
Traditionally there have been two types of paint: latex, and oil based. Oil based paints are either alkyd or linseed oils; the former being synthetic polyester resin made from alcohols and acids, the latter a natural oil extracted from the dried, ripened seed of the flax plant. Oil based paint is more durable and takes longer to dry. Clean up requires paint thinner. Latex paint is water based and is therefore much easier to clean up. Oil based paints have been virtually removed from the market due to the environmental damage they cause and as a result, latex paint has dramatically increased in quality. Because of its smooth surface, you cannot paint over an oil based paint with latex because it will not adhere. Also, until the 1960s, oil based paint contained lead which is very harmful and, until 2010, latex contained mercury.
What is the latex in latex paint? Latex is a natural product that comes from the sap of the Brazilian rubber tree. When Latex paint was first developed in the 1940s by Sherwood Williams, it used the natural rubber as a binder, more on that in a moment. Today we use synthetic polymers which look like latex but have a different chemical makeup.
Paint contains 4 components:This is why most experts refer more accurately to water based paint as acrylic emulsions. In a moment I will discuss the various components of paint, but with latex paint, the so-called latex component is the binder that sticks to the surface when dried, whereas the water is the solvent that keeps it in liquid form until ready to be used. In an oil-based paint, oil is the binder and paint thinner is the solvent. Paint requires something to both attach the pigments to the surface when dried, and something to keep it liquid until you are ready to paint.
Pigment – colors in all their varieties. It comes as a dry colorant ground into a fine powder. This is then added to the binder. Here is an interesting website that provides some history on the topic:
Solvent – the volatile substance that dissolves the binder and keeps the paint in liquid form until ready to be used. The faster the solvent evaporates, the faster the paint dries. The rate of evaporation is called volatility. Too slow and the paint will sag, too fast and you get orange peel (textured imperfections in the paint, like the skin or peel of an orange), too much and the paint will be too thin. Examples of solvents include turpentine, mineral spirits, turpenoid, lacquer thinner, denatured alcohol, MKE (methyl ethyl ketone), kerosene, gasoline, acetone and of course water.
Binder-the glue what holds the all the paint components together and sticks them to the surface being painted. Binders are made of two types of polymers: thermoplastic which hardens when the solvent evaporates or thermosetting which requires a chemical reaction as well as solvent evaporation.
Additive – product that can be added to give paint special characteristics such as
- wetting and dispersing – additives break down the surface tension of paint particles so that the surfaces will be covered by the binder. Also, since solids like to clump together, another additive ensures that the paint particles disperse evenly throughout the liquefied binder. Otherwise you would have to constantly shake the can of paint until you use it.
- flow and levelling – prevents unsightly brush and roller marks after the paint dries. Helps ensure a smooth and consistent film.
- defoamers and dearaters – they prevent bubbles from forming and prevent air from mixing into the solution.
- Rheology (flow of liquid) modifiers and catalyst and driers – helps the paint to flow and dry evenly. A catalyst helps the transformation into a nice finish.
Varnish and Stain
Paint, in its most general definition, includes paint, varnish and stains; however, more specifically, the term ‘paint’ refers to a coating that covers the surface whereas varnishes and stains permeate the surface.
Varnish does not have a pigment. The purpose of a varnish is to protect the surface while maintaining its original color and appearance. It enhances the surface and provides a smooth gloss.
Stains provide color without hiding the original appearance. The stain allows the wood grains to show through. Paint on the otherhand, puts a coat over the surface. Stain absorbs into the surface.
Stains are distinguished by their binders(http://news.thefinishingstore.com/index.php/seven-types-of-stain/)I discussed previously the differences between water and oil based paints. The same rules apply to stains, but you also have to factor in the type of wood you are using. For example, if you are staining a wood that is natrualy resistant to rotting such as cedar, cypress or redwood, a water based stain may be preferable. Wood that is exposed to the elements would fair better with an oil based paint which is more durable. Rather than trying to decide which one is better, it is better to understand that they each serve a different function. If you determine the function you need it to serve, you will have a better time selecting the type of binder used in the stain. The various binders available for stains include:
- Oil Stains – made from linseed oil or synthetic polymers as the binder. It takes longer to dry, but it penetrates the wood better and is very durable, providing a thicker seal than water based stains. As such, it requires less long term maintenance.
- Varnish Stains – made from a resin dissolved in a liquid. A resin is sticky, flammable, organic material that, in the case of varnish, exudes from plants and is insoluble in water. Resins dry hard like an oil based paint. They use the same thinner as oil based stains. They are harder to use than oil based because you have less time to wipe off excess varnish and can leave brush marks. It is often used on wood that is already stained.
- Water Based Stain – easer to use, easer to clean up, easier on the environment. They do not bond well over oil or varnish surfaces. They tend to raise the wood because of the water content, and they dry faster. You should wet the wood first and then sand off any raised grains. This way when you apply the stain, the wood will not expand any further
- Gel Stain–gel suspended in an oil or vanrish binder. It is much thicker, similar to mayonnaise, but does not result in blotching. Soft woods can have varying densities and will therefore absorb stains inconsistantly, leaving irregular coloration. Gels do not have this problem because they lie on the surface, covering porous and nonporous areas equally . Best to use on pine, maple, cherry and birch which have relatively nonporous surfaces and do not absorb stains well. It does not work well on wood with tight corners, nor on porous woods such as oak, ash, mahogany and walnut because you want to bring out the grains.
- Lacquer Stain – a liquid made of shellac dissolved in alcohol, or of synthetic substances, that dries to form a hard protective coating. Shellacis a resin as is varnish, but rather than coming from a plant, it is secreted by the female lac bug. It is produced as dry flakes and is dissolved in ethanol to make liquid shellac.
- Water-Soluble Dye Stain – these come as a powder and must be mixed with a solvent.
- Metal-Complex (Metalized) Dye Stain
Which is better, paint or stain? Paint creates a new surface and provides protection; stain maintains the appearance of the substrate and even enhances its colors and texture. Stain protects the beauty of the wood, paint protects the longevity of the wood. Stain wears away gradually and can be easily restained, paint can start to peel and may need to be scraped away prior to repainting. Since paint protects the surface, you would likely use paint on a wooden handrail. Paint lasts longer since it is a thicker coating. It is a matter of what type of look you are going for, and ease of use.
Do all surfaces need to be painted? Wood certainly requires paint or stain in order to keep it from rotting. But what about concrete? Concrete is highly porous so it is certainly a good idea to seal the concrete that is exposed to the elements, however it does not necessarily need to be painted. It is a matter of preference. Concrete is pretty bland, but once you start painting it, you cannot go back to bare concrete.
When painting concrete, as with all surfaces, be sure to thoroughly wash the surface first. There are many concrete high rise apartment buildings with peeling paint. This is commonly because the owners did not spend the money to have the surface thoroughly cleaned first. The cost of cleaning can almost be as much as the painting itself but never cheap out or you will find the paint peeling away within a year.
Newer construction often uses composite boards. These are often coloured all the way through so they can retain their color for a very long time; nevertheless over time the sharpness can fade. They may not need the regular painting of the wood trim, but they should be brightened up from time to time. Also, color’s go in and out of style so you may want to change the color. Darker colors fade faster.
Some fundamental tips on painting:
The surface must be dry and clean.
Do not paint if the ambient temperature is below 10 degrees Celsius or 50 Fahrenheit. Do not paint if it the air has high humidity, for example if it is foggy outside or if it just finished raining.
And there you have the Facts of Paint.