Colouring our world

By - , Build 76

We all know which colour or combinations of colours we like best — each choice is personal and based on a number of factors. But take care, your choice may impact on the durability and maintenance requirements of your building.

Stable substrates, in this case concrete block masonry, are more tolerant of darker colours.
Darker colours can accelerate cracking and failure of the paint. Paint on horizontal surfaces will also deteriorate faster than on vertical surfaces.

The quality and durability of any finished paint work is directly related to the effort put into preparing the surface to be coated, and the type and colour of the paint being used. There is more to choosing a paint colour than simply personal preference. You must also take into account the:

• material being painted

• effect a particular colour may have on the material or element

• effect the colour may have on the durability of the coating itself

• historical considerations — is the colour appropriate for the age and style of the building?

• effect of the environment on the coating and the appropriateness of the colour for the surrounding area.

Materials

Paint finishes on cement-based materials (concrete, cement plaster, fibre-cement products) tend to last longer than paint on timber because timber moves more in response to temperature and moisture changes.

Paint on wide timber boards generally doesn’t last as long as paint on narrow boards because the overall movement in wide boards is greater. Dark colours applied to wide (>100 mm) timber boards will have a very limited life.

A dark colour applied directly over a light one can cause a previously sound coating to lose adhesion. This is because the dark colour generates higher temperatures. The result is increased movement and damage to the bond of the underlying coating to the substrate.

Surface temperatures of a cladding material will generally be higher where insulation is installed directly behind the cladding. Generally the greater the insulation value the higher the temperatures.

Effects of colour

Paint colour can have a significant effect on how durable the paint coating will be. Therefore it’s worthwhile considering the effect of particular colours and how this may impact on the underlying material.

Different colours reflect different amounts of light from their surfaces. Dark colours generally have lower reflectance (matt black has a reflectance of 0%), with reflectance increasing as the colour lightens (white reflectance is 100%). All coatings fade and chalk but it’s usually less noticeable on lighter colours with higher reflectance.

Lighter colours tend to last longer than darker colours on less stable substrates, such as timber, because movement in the substrate is reduced. Dark colours can outperform light colours on more stable substrates, such as concrete or render/plaster. For metal and plastic claddings, darker colours significantly increase the amount of thermal movement, which must be allowed for at the design and installation stages of a project.

Darker colours, with low reflectance, can cause excessive drying and shrinkage in timber, which in turn can:

• accelerate cracking and failure of the paint

• increase the incidence of resin-bleed through the coating.

Lighter colours significantly reduce surface temperatures so there will be less thermal movement.

Some colours are better at covering other colours. For example, bright yellows, reds and oranges have limited opacity and may require additional coats to effectively cover the original coating. Darker colours are more difficult to colour-match if making repairs.

Lighter colours are less likely to show substrate defects and impact damage because they are more effective at reducing shadow effects.

Paint types and application

There are two main types of paint — water-borne and solvent-borne — and each has advantages and disadvantages when compared with the other. They also each have slightly different surface finishes.

Water-borne paints

Water-borne paints are more flexible when aged, making them more resistant to cracking, and are generally more durable. They are quicker drying, although this makes maintaining a wet edge more difficult. They are more permeable to water vapour, but the degree of permeability reduces in proportion to the amount of resin in the formulation. Finally, they are better at retaining gloss and colour.

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Solvent-borne paints

Solvent-borne paints are generally better suited to high-wear surfaces as they are more resistant to scratching (although also more likely to chip). They are more water and water-vapour resistant, are slower drying (except for spraying enamels and two-component coatings) and have higher initial gloss. But they must be applied to dry surfaces, are more volatile and should not usually be applied over water-borne paints.

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Gloss levels

Matt finishes make defects in the surface less obvious while semi-gloss and gloss finishes highlight them. As the gloss level decreases the amount of light reflected by the colour decreases, so matt finishes will always appear darker than glossy finishes of the same colour.

Gloss paints tend to highlight variations in application (e.g. where a good wet edge has not been maintained during application) but are easier to keep clean.

Water-borne and solvent-borne paints of the same colour used adjacent to each other may appear different once applied because of differences in manufacture and relative gloss levels.

Last words

In the end the quality and durability of any finished painting or coating job depends largely on the effort put into preparing the surface to be coated.

New paint applied to existing painted surfaces will last better if the old paint is still in a reasonably sound condition. Sufficient coats must be applied to achieve the recommended finished coating thickness.

Ensure air and surface temperatures are within the paint manufacturer’s recommendations, typically within 10–35°C during application, although some waterborne paints may be applied in temperatures as low as 5°C. Applying the coating in low temperatures can lead to loss of gloss in solvent-borne coatings and failure to form a cohesive film in water-borne coatings. Also, drying times will be longer, increasing the risk of dust and other debris being deposited on the coating.

Use coatings manufactured by a reputable paint manufacturer who will provide a back-up service. The price of the coating is usually only a small part of the total cost of a well-done paint job, so don’t compromise on paint quality.

Stable substrates, in this case concrete block masonry, are more tolerant of darker colours.
Darker colours can accelerate cracking and failure of the paint. Paint on horizontal surfaces will also deteriorate faster than on vertical surfaces.

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Articles are correct at the time of publication but may have since become outdated.

Stable substrates, in this case concrete block masonry, are more tolerant of darker colours.
Darker colours can accelerate cracking and failure of the paint. Paint on horizontal surfaces will also deteriorate faster than on vertical surfaces.

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