We probably all understand the difference in taste (and experience) between a milkshake that is made with three scoops from a tin, thrown into a glass of skim milk and one that is made by mixing double-cream flavoured ice-cream, maybe with a dollop of flavoured-syrup or added cream. It’s true that we might call both of them a chocolate milkshake, but there is no doubt about which holds the superior taste experience (and added calories).
All paints are not created equal, so simply specifying two coats of paint for your redecoration, is like simply asking for a chocolate milkshake. The experience is not going be the same. For one, your double-thick shake will very likely leave you full and satisfied. Your skim milk shake will go down a lot quicker and may leave you tempted to grab for a second drink, or maybe even a third, before being satisfied.
Two coats of a cheap, low quality paint will not provide the same coverage or finish as one coat of a high quality industrial paint, nor will it last as long. Over a ten-year period, you might find that with the low quality coating, you will need to repaint two or three times. A good quality industrial coat can easily last the full ten years or even longer. So what determines the lifespan, quality and durability of a given paint system?
There are actually a lot of factors involved in the application, but for purposes of this articles, we want to focus on the paint product and the ingredients involved in making that paint. To understand what makes up a high quality can of paint, we must first understand that there are four main raw materials used in paints, namely 1) solvents (or water), 2) pigments, 3) resins (binders), and 4) additives.
Solvents refer to various low viscosity, volatile liquids which can dissolve a resin. Solvents include petroleum mineral spirits and aromatic solvents such as benzol, alcohols, esters, ketones, and acetone. Water is used in many paints. The solvent makes up the liquid portion of the paint which makes it easier to apply, but evaporate as the coating dries. A paint with a higher volume-to-solids ratio will contain less solvent and more pigment and resin which form the coating on the wall once the solvent has evaporated and the paint is dry.
Pigments are simply insoluble, finely ground materials that give paint its colour. Titanium dioxide is the most common pigment as it is used make basic white paint.
Resins are used as a binder in paint. Resins can be translucent or transparent, solid or semi-solid. The nature and amount of binder determines much of a paint’s properties, such as washability, toughness, adhesion, elasticity and colour retention.
The last category of raw materials in paint are additives, which can serve many purposes, from reducing the drag on a brush, providing anti-slip characteristics, adding texture, etc. There are many different paint additives, such as driers, anti-settling agents, anti-skinning agents, defoamers, silica (or sand) for texture, mildewcide, perfumes and a host of others that enable paint to cover well and last long. Some, like calcium carbonate and aluminum silicate, are simply fillers that give the paint body and substance without changing its properties.
Application of a paint consisting mostly of solvents may be easy, but when the paint dries it leaves behind less of the other raw materials on the walls. This sort of paint may only have a 28-30% volume-to-solids ratio and so when the paint dries the thickness of the paint film that is left on the wall is relatively thin. A material data sheet on is available for all paint varieties. On this sheet you will find both volume-to-solids information, as well as DFT or dry film thickness information. If most of the remaining materials in that paint are fillers, like calcium carbonate, then your walls may look fine after a two coat application, but the coating will not last very long.
The dry film thickness (DFT) of paint is measured in microns (µ), which is a thousandth of a millimeter. Many commonly used paints produce a dry film thickness of around 25-40µ per coat, so a two coat application will leave your wall with a film thickness of 50-80µ.
A high quality paint with a higher volume-to-solids ratio will produce a thicker film when it dries. Ideally, the other raw materials, such as the resins, should help to contribute toward a quality coating that will last for a number of years, or even decades. Some elastometic coatings, made with a high-quality resin, could obtain DFT’s of between 300-400µ for a two-coat system. This sort of coating, in the right environment, can last two or three times longer than other inferior coatings.
It is important to specify a minimum dry film thickness (DFT) rather than arbitrarily insisting that a contractor apply two coats of paint, or alternatively to specific a certain quality of paint.
The outside label or even the manufacture behind a can of paint is not as important as understanding the ingredients inside the can. Work out the cost of three scoops of powder into a glass of skim milk, versus mixing the best double-cream ice-cream, adding syrup, a wallop of cream and chocolate sprinkles. One cannot blame paint manufacturers, who are business to make profits and who often incentivise their technical consultant to move the product with the highest margins. However, it is always good to understand what is inside the coating that you are been recommended and what alternatives there may be.
There are a number of factors that go into determining whether or not a paint application will last only four years or ten years of longer. The ingredients in the tin is only a small part of the many factors, but an important starting point.
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