Coating buildings to last a lifetime

by Darren
Coating buildings to last

Last on the building, but first to make an impression, coatings and paints need to be carefully specified to prevent failures.

The coating or paint application is typically the last step of construction, but one of the first things people see. And since an application is often judged on face value, there is a lot of pressure on suppliers and applicators to get it right, on time.

This takes careful project planning and skilfully trained applicators who can work under the pressure of tight deadlines.

In addition, according to Babette Mattheyse, project manager at Versus Paint, a coating is only as good as the surface it is applied to. “One of the biggest issues affecting both paint and coating applications is the plaster underneath it, which in turn can be affected by either the product mix or the application,” she says.

“If there are cracks, water that enters will cause the brick masonry and plaster substrate behind the paint to expand. Water also leaches Portland cement paste out of the cracked surfaces, thereby softening and weakening the plaster adjacent to the cracks. It furthermore transports water soluble salts, particularly calcium hydroxide from within the cement paste to the surface where these salts are precipitated at the plaster or paint interface. The expansion of these salts at the interface caused the paint film to blister and delaminate, a symptom called efflorescence,” Mattheyse explains.

“Therefore surface preparation and plaster evaluation are crucial in ensuring that the surface is acceptable. If the surface fails, then the coating will also fail.”

Covering up imperfections
What’s more, while uneven plaster surfaces won’t necessarily cause failures, the flaws are unsightly and detract from a building’s appearance. “This is the reason why coatings and cladding are so popular nowadays, because they are able to conceal imperfections,” Mattheyse states.

“For rough bricklaying and uneven plaster, it is wise to choose a coating with body. While trowelled-on coatings follow the surface, ones that get sprayed on give a matt, rough finish that absorbs light and doesn’t show the defects,” she advises. “It is typically a product that is about 5kg/m², compared to a paint system which is about 1l/m² for a primer and two or three top coatings.”

Mattheyse adds that the most expensive element in any painting or coating project is the cost of labour so it makes sense to apply a quality product that exceeds the norms in terms of durability, thus reducing the need to repaint by several years.

Trendy coatings
•    Europlaster
Regaining popularity since its glory days in the 80s, Europlaster, a quarts-based acrylic plaster textured with sizing stones, is back with a courser, rougher texture than before. It has been specified for City Lodge in Newtown as well as Mall of Africa.

•    Eurospray
A favourite for many new builds in Sandton, Eurospray is an acrylic-based coating sprayed with either a compressor or a hopper gun. However, the design of a building needs to be considered first since every surface area that is not supposed to be coated, such as glass surfaces, needs to be taped shut before spraying.

•    Natural stone (as seen at the Maxwell Office Park in Waterfall City)
To achieve a similar effect as with Eurospray, without the hassle, a natural stone coating can be applied together with a pigmented sealer or a natural colour stone.

•    Polish plaster
For building interiors, polish plaster is often applied with a spatula over gypsum plaster. Polish plaster consists of crushed marble in an acrylic paste, which is sanded down after application and finished with a wax coat to achieve a glossy finish.

•    Comb plaster
Seen in a variety of new builds such as Lynnwood Bridge Phase 3, comb plaster is another popular choice for both interiors and exteriors. Comb plaster can add about 7 to 8kg/m² and needs to be applied by a trained professional in order to get a neat finish.

•    Dark coatings
To create the illusion of floating buildings, architects often go for dark coatings at the bottom of buildings to create a black base, while the top of the building is either cladded or coated.

•    Limewash paint
Pure acrylic lime wash can be applied onto red travertine bricks or a similar surface to create a white lime wash appearance on the surface, as seen at the Middelburg, Heidelberg and Woodmead shopping centres.

Trends courtesy of Babette Mattheyse from Versus Paint.

Restoring the “old ladies”
When refurbishing ageing buildings, the surface is just as important to evaluate as on new builds. It is not always sufficient to just fix a crack or two and slap another paint coating on. With 21 years’ experience in the industry, Brigitte Prior, executive at Promac Paints, warns that should the coatings on a wall reach excessive thickness or if the old layers aren’t properly assessed, it could end up costing asset owners a lot of money as one can get delamination.

“Delamination occurs at the substrate primer interface,” she says. “There are two distinct types of failure: adhesion between layers of paint and cohesion within a given layer of paint. Upon inspection of these issues, new coatings have always adhered well to old coatings but the layers underneath have lost their adhesion and flexibility properties, causing them to pull away,” she explains.

According to Prior, this issue can be reasonably unforeseen and may only become an issue when new coatings are applied, so the case of who is responsible becomes unclear. Even when adhesion tests are done on the old coatings, they may appear sound but because there are so many layers, sometimes up to +300 microns, they are brittle and their adhesion becomes limited.

“A common cause of delamination occurs with a change of colour from a pale to a much darker topcoat” Prior adds. “The extra heat associated with the darker colour, changes the tipping point and delamination occurs.
The issue can be avoided by identifying the age and build-up of existing coatings and fully removing the old layers to create a sound substrate suitable for painting.

To ensure a fail-proof revamp, Prior recommends a three-step process:

1.    Do a thorough assessment.
Looking at the macro environment, factors such as UV, light, wind, rainfall, temperature, salt contamination and humidity of the area need to be considered, while the micro environment assessment will include extreme temperatures, dew point, industrial fall out, chemicals, high traffic and high maintenance like washing and scrubbing.

2.    Determine correct surface preparation and moisture levels.
The surface must be cleaned correctly with all loose and flaking paint removed and cracks repaired. Should there be cracks in paint, there could be moisture in the wall that will cause inherent problems. It is important that moisture levels are below 8% and that surface temperatures are not excessive. It is also necessary to waterproof all parapets, ledges and sills to eliminate moisture ingression.

3.    Choose a light colour
To play it safe, go with lighter colours when painting over old coatings. Dark colours attract more heat and if there is moisture in the walls, bubbles will form. Dark colours expose walls to the volatility of heat up to 30% more than light colours.

Paint advice:
•    For water-based emulsion coatings, the acceptable moisture level content of the substrate to be painted is 15% or less, as measured by a moisture meter.
•    A recommended paint coating specifications system consists of a three-stage multiple components application process, including a primer, intermediate/undercoat and full finish coat.
•    This application process needs to be accompanied by proper surface preparation (including a moisture content check), compliance with the right painting weather conditions, use of good quality products, application tools and qualified applicators.

Advice courtesy of Tracy Robinson and Helen Gurura from Dekade Paints

Specifying with a purpose
When it comes to specifying paint or coatings for new or old buildings, it is important to ensure that a suitable coatings system is applied to the relevant surface.

Selma Leach, an industry expert with 24 years’ experience, believes that one of the biggest challenges in the paint industry currently is the lack of expertise, which result in incorrect specification, which in turn lead to failures. Technically-minded sales representatives are scarce and though architects and specifiers can approach retailers for information, this is not advisable for corporate projects, which are often guarantee driven.

“It is important for specifiers to get the right information,” she says. “Many paint companies offer standard generic specifications that include the substrate, correct preparation method and finishing coats, which is a great place to start, but ultimately, every building and substrate is different. Knowing the finer detail is extremely important and by involving a paint professional to cast an expert eye on the building, one can be sure to get the correct specification.”

Instead of just throwing paint at a problem, Leach stresses the importance of properly assessing existing flaws in a building. “Once you understand the condition of a building, the paint specification becomes ABC,” she says.

“The Dry Film Thickness (DFT) on a standard plaster primer is about 35 – 45 microns thick, while two smooth top coats will add between 30 and 40 microns each, so ultimately the paint system will come to about 120 microns, which is only 0,12mm thick. Since this thin film of paint is expected to protect a building surface, it is imperative to ensure, as a basic requirement, that the substrate is sound, clean and dry. Coupled with an appropriate system and no underlying construction or waterproofing issues, failures are highly unlikely,” Leach states.

Helen Gurura, exclusive marketing manager and architectural colour specifications consultant at Dekade Paints, adds that a paint specification should be functional and geographic-specific to cater for the fluctuating climatic and weather variables.

“Humidity, moisture, intense sunlight and temperature extremes are some of the core elements to consider. A product has to be matched to its intended function to ensure longevity and success of the coating system,” she states.

According to Gurura, local paint manufacturers are developing products that are highly functional, adaptable and optimally suited to counter some of these conditions, which have a direct impact on the performance of a coating system.

New developments
One of these is the development of an adhesion-promoted, pure acrylic, low-sheen coating with stain and dirt removal properties suitable for South Africa’s coastal and highveld climatic conditions. It is specially designed to counter some of the common moisture-induced paint problems.

“The product’s advanced hydrophobic formulation allows the paint to breathe, thereby releasing trapped moisture from inside the walls, repelling water on the surface and preventing water from seeping back into the wall,” Gurura explains. “It also contains inhibitors to prevent fungal and mould growth on the painted substrate, while the incorporation of colourfast pigments further enables longer colour retention on exterior exposure.”

According to Leach, development of fibre-reinforced acrylic coatings further assists with great flexibility and bridging ability over hairline cracks. “In addition, these products can either be applied to a soft ripple or formed into a texture with application technique.”

Mattheyse adds that new technology now also makes it possible to improve various paint properties that gives paint the ability to cover slight plaster defects. “This technology offers water and stain resistant durability and wash-ability and meets the most stringent environmental and VOC regulations,” she states.

To ensure the successful application of paints and coatings, it is advisable to get first-hand advice from the experts to help select the most appropriate coatings for a project and ultimately get a finish that will both look great and last.

Full thanks and acknowledgement go to Promac Paints, Versus Paint and Dekade Paints for the information given to write this article.

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