How to assess paint coverage and durability

Introduction

Although paint is a popular product choice for enhancing appearance of building exterior and interior, it is worth remembering that paint properties extend beyond its visual impact. Paint coverage and durability are significant quality criteria, allowing for more precise product choice, reduced wastage and longer lasting paint film. Criteria for durability and coverage are also included in the product evaluation for environmental excellence labels, for example the EU Ecolabel.

This blog post will provide an insight in the paint coverage and durability qualities as well as provide useful tips anyone can follow in order to improve these qualities, therefore allowing for better understanding of different paint products and their quality, when preparing for a painting project.

What is paint coverage and durability and why it matters?

Paint coverage and durability assessment is necessary in order to reduce the costs associated with a painting project, but more importantly — to reduce paint product environmental impact that consequently happens when resources are overused or wasted.

Paint product coverage and durability requirements can vary greatly depending on the type of surface being covered. For example, spreading rate will depend on the quality of surface while durability mostly will depend on the location of the painted surface (in the indoor areas as well as outdoor areas with intense movement of people paint film is susceptible to more wear and weathering than in areas with less intense movement and consequently with less frequent cleaning).

The EU Ecolabel (leading environmental label in Europe) require paints to comply with certain efficiency requirements, that include evaluation of the paint product coverage or spreading rate as well as durability requirements. Becoming familiar with such product criteria empowers consumers and professionals to choose the most suitable paint products for the intended project. (a)

Paint coverage describes the spreading rate of paints and coatings on a given material or surface. Paint coverage is typically indicated on a product label as square meters per litre of product. Knowing paint coverage helps in planning of the painting project since it provides information on the necessary amount of a paint product for a given size of a surface. This knowledge allows consumers to save money as well as reduces amount of waste  generated from the painting project.

Durability of paint describes resistance of an applied paint product to mechanical exposure and is measured by combined assessment of paint film washability, wet abrasion and scrub resistance ultimately indicating the ability of dried paint film to resist wearing and degradation.

Paint coverage assessment

Paint coverage assessment allows for a better idea of the amount of paint necessary for a painting project, thus avoiding both — overpaying for unnecessary product and waste of resources. The paint coverage depends not only on the surface but also on its wear and tear conditions. The paint coverage is expressed as the spreading rate of paint and is typically indicated on paint packaging as square meter value per litre of paint.

Preparation for a painting project should also include the surface evaluation stage when calculations of the surface area as well as evaluation of surface quality and conditions are being made. The calculations can be done by multiplying surface hight by surface width and subtracting the window and door surface area. The quality estimate of surface as well as the type of paint chosen will determine the recommended number of coats, which is also one of the criteria to be included in the paint value and price estimations.

Approximate paint coverage depends on the type of paint. The spreading rates for the most popular types of architectural paints are defined by EU Ecolabel. Paint coverage requirements for the EU Ecolabel refers to white and light coloured paints and are defined as the spreading rate of paint. These requirements refer to the minimum surface area that one litre of paint can cover. For indoor paints it should not be smaller than 8 m²/l and for outdoor paints it should not be smaller than 6 m²/l (a).

How to improve paint coverage

Paint coverage or the area that certain amount of paint will cover highly depends not just on the paint coverage indicated on the paint label but also upon the pre-existing condition of the surface and the overall project preparation done in advance. In order to ensure good quality of the painting project as well as to reduce the necessary amount of paint, certain steps should be followed:

• Choosing of the right tools and the right technique for painting. The losses due to the application method are 4-10% for brush or roller application, 50-60% for air spray and 45-50% for airless spray. Possible paint losses also depend on the shape of surface, atmospheric condition and height of the painting project location. Losses can happen also as a result of paint spillage during handling (b).
• Choosing of the most appropriate paint product for the given surface. It is important to choose between masonry, wood or metal paints and take into account the withering conditions surface will be susceptible to, therefore indoor paint should be used as interior coating and outdoor paint should be applied as exterior coating.
• Preparing and cleaning of the surface. Surface preparation is one of the key steps determining the durability of paint film. Based on the coating type the surface preparations may vary. General rule of thumb is to have an even, clean and dry surface (c).
• Applying of primers and undercoats. In order to protect the surface substrate against moisture, avoid stains and provide advanced adhesion of paint, surfaces should be primed in accordance with the requirements for  a particular surface substrate material (d).

Paint durability assessment

Paint durability describes the resilience quality of dried paint film to withstand routine maintenance like wiping, brushing, cleaning. These elements all together are described as paint washability, and typical testing of paint requires evaluation of its wet-scrub resistance.

Wet-scrub resistance (WSR) indicates the resistance ability of a dried paint film to wearing and degradation. Evaluation of scrub resistance shows how resistant paint film is to the surface clean-up when surface is being washed and brushed, showing if any softening, thinning and blistering of film takes place. Therefore, if visual changes in paint film can be observed, then the given product has poor scrub resistance (a; e).

In the EU, five resistance classes are defined to assess the coating resistance specifically to damp wiping. Resistance classes number 1 and 2 indicate the highest abrasion resistance and cleanability, therefore indicating that paint will be longer lasting and will require fewer re-paints, while the cheaper paints of class 4 and 5 are not sufficiently cleanable (scrub value indicates the amount of wash cycles done during testing; μm values indicate the reduction of paint film):

 

Class 1

• < 5 μm at 200 scrubs
• Suitable for cleaning with water and natural brush if neutral or hygienic cleaner is added. Applicable for extremely burdened indoor areas such as entrance halls, kitchens, staircases or public buildings.

Class 2

• >5 μm and < 20 μm at 200 scrubs
• Suitable for cleaning with water and natural brush if neutral cleaner is added. Applicable for ceilings and walls with heavy usage such as children's rooms and bathrooms.

Class 3

• >20 μm and < 70 μm at 200 scrubs
• Suitable for cleaning with water and cloth if neutral cleaner is added. Applicable for ceilings and walls with normal usage such as living rooms.

Class 4

• < 70 μm at 40 scrubs
• Suitable for cleaning with dry cloth. Applicable for ceilings and walls in living rooms.

Class 5

• 5 >70 μm at 40 scrubs.
• Applicable for ceilings in living rooms. Resistant to dry wiping (a).

Paint durability requirements for the EU Ecolabel

The EU Ecolabel requirements for durability can be found under the requirements for paint product efficiency and the list includes spreading rate (only for white and light coloured paints, including the white base paints used in tinting systems), resistance to water, adhesion and abrasion, weathering, water vapour and liquid water permeability, fungal resistance, crack bridging as well as alkali and corrosion resistance.

All indoor wall and ceiling paints (tinting base and with a white pigment content above 25 g/m² of dry film (with 98% opacity)) awarded with the EU Ecolabel must meet class 1 or class 2 wet-scrub resistance.

Read more about sustainability and paint product performance in our blogpost: link

How to improve paint durability

Similarly to the improved paint coverage, the paint durability can also be enhanced by adequate surface preparations and appropriate choice of paint. Advance preparation for a painting project should include evaluation of the surface location - how much wear and tear it will be susceptible to, whether it is indoor or outdoor surface as well as how often it will be cleaned.

Additionally, becoming familiar with the criteria of EU Ecolabel or other environmental label awarded to paint products can allow for a more straightforward product choice, since products awarded with environmental label are by default tested for paint durability in order to receive the certification and associated product marking. Find out more in the EU Ecolabel User Manual.

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Closing

Paint coverage is the spreading rate, describing how many square-meters can be covered by one litre of paint. This information allows for a better estimate for the required amount of paint thus avoiding wastage of resources and money. Paint durability describes the resistance of paint film to wiping, brushing and washing, similarly providing estimate for the longevity and performance of paint.

Generally, for purchasing of architectural paints, it is advisable to opt for paints awarded with an environmental label, since the quality requirements include (among other criteria) the requirements for paint product efficiency,  that includes spreading rate and durability.

Paint coverage and durability assessment can help to reduce the costs and waste associated with painting projects and can ensure better long-term surface protection. To ensure better surface coverage and durability it is important to include surface evaluations, calculations and necessary preparations as an integral part of the painting project.

 

Author: written by Anse Romančuka, edited by Linda Kikuste