Science Behind Paint

WHY PAINT

Paint is a surface coating which decorates and protects the surface on which it is applied. The success or failure of any coating is influenced by the following factors:

  • Substrate condition
  • Surface preparation and method of application.
  • Environmental condition at which the paint is applied
    and expected to withstand during service
  • And last but not least, the quality of paint used.

No paint is good if not applied properly. This is borne out by the fact that paint in the real sense is not a finished product. The consumer requirement is deemed to have been met only when the liquid paint is applied on a surface and the film is formed i.e. the paint dries. The aforesaid factors influence the realisation of the consumer requirement.

In architectural finishes like exterior paints, the decorative angle occupies a predominant position but the protective properties also play their role silently.

Modern houses are made up of concrete and bricks which are porous in nature and allow water to penetrate. Concrete is highly alkaline by nature and hence protects the reinforcement made of steel from corrosion. However, carbon dioxide from the atmosphere reacts with the alkali in the cement forming calcium carbonate, which gradually reduce the alkalinity of concrete exposing the reinforcement to attack of corrosion. This cannot happen in a dry condition; but in the presence of water coming through the plaster the reinforcements get corroded and weaken the structure. Since corroded material occupy more volume than the steel, they push the plaster out culminating in cracking and flaking.

The painting of an exterior wall serves both the purpose of preventing carbon dioxide and water penetration into inner parts of concrete protecting the reinforcements and structure.

A well formulated paint fortified with effective biocides protects the surface from the attack of micro-organisms like fungi and algae maintaining its original beauty.

One important point to be remembered while painting is that, no paint film is stronger than the surface on which it is applied. Surface defects, like rising dampness, leakages, cracks, microbial growth, etc. should be well attended to before taking up the painting job. Post painting remedial measures are always cumbersome and does not offer permanent solutions.

Incidentally, the causes of paint failures are the factors without which life is impossible on earth. They are earth, water, air, heat and light. And of course there are the man made hazards like industrial environments and gases.

Once you get on the job of painting you will realise that the time spent on the preparation of surface is much more than that required for the actual application of the paint. In total analysis this exercise is worthwhile because most of the paint failures arise from poor surface preparation. The first step before any painting is the thorough inspection of the building, checking for peeling paint, cracks, leakages, rusty nail heads and microbial growth. In short, the success or otherwise of any painting job will be decided by the above factors.

What is Paint

Paint can be defined as a fluid material which, when spread over surface in the form of a thin layer, will form a solid, adherent and cohesive opaque film.

Some paints are also available in form of powder. They are either converted to fluid form by addition of suitable thinner prior to its application or applied directly.

E.g. Dry Distemper, Cement Paints, Powder Coatings, etc.

The fluid paint consists of four major ingredients -

what-is-paint-diagram

Pigment, binder or film former, and solvent or thinner, and the relative proportions of these ingredients can be varied to produce films with any desired physical and application characteristics.

The functions of major ingredients are as follows:-

Pigment:

Pigments provide colour and opacity (or hiding power), enhances film durability and hardness and, in metal primers, inhibits corrosion. Lamellar pigments are used to reduce the moisture permeability of films.

Binder or film former:

Binders bind or “cement” the pigment particles into a coherent film which adheres to the substrate. In modern paints, the mechanical and resistive properties of the film are controlled very largely by the binder.

Thinner or Solvent :

They are used to render the pigment/Binder mixture sufficiently fluid for the transfer from one tin / vessel to another and also for application to a surface in the form of a uniform film. The thinner should then evaporate completely to leave a film consisting of pigment and binder only.

Thinners in common use include a wide range of organic solvents (hydrocarbons, alcohols, esters, ketones, etc.) and water (in Latex emulsion and water soluble paints).

Additives :

Additives are present in small quantities (1-4%) which perform specific but very important role.

composition-of-paints

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