Technical Corner: The basics of coloured paving

TEXT BY NADJA PAUSCH

Many designers are hesitant to include coloured products in their designs as they have seen too many failed applications. The most ubiquitous criticism of coloured products is that they have a propensity to fade quickly and weather poorly, turning vibrant reds into what a mentor of mine described as “cat food pink,” often within a few years. Another problem is that colours on-trend during the design phase may appear dated a few years later, potentially even by the time project construction is complete.

Coloured materials in paving applications can be one way to introduce colour to a design. The suitable selection of materials, colours, and textures can enhance the aesthetic of a project at a relatively low cost. However, with so many options and competing information, it can be difficult to discern which material is best. What follows is a brief overview of a few of the most commonly used coloured paving solutions.

Natural Stone
Natural stone, when sourced appropriately, is one of the most reliable materials to utilize in the landscape. The main consideration is to ensure the stone is hard enough to endure our climatic conditions–for example, limestone can vary significantly in hardness depending on the region in which it was quarried. Proper detailing (primarily of the base assembly and joints) and installation of stone products is important to ensure lasting value. When properly installed, the maintenance requirements of natural stone are minimal. Granite is a notably well-performing option; it is an extremely durable material and will provide lasting colour and texture. Its strength makes it an appropriate solution even for commercial applications. Limestone, slate, and travertine work well in pedestrian applications. Stone can also offer a wonderful range of colours, including reds, purples, and greens, along with the common range of buff and grey tones.

Clay Brick
The colour of clay bricks (usually ranging from white/buff to deep red and black) is due to the varying mineral content of the raw material, which is formed and fired in high temperatures, and, like natural stone, will not fade over time. Despite the colour steadfastness of this material, brick does not always weather well in our northern climate, commonly due to installation issues rather than product failure. That is, brick requires proper installation in order to remain durable in the landscape; it should be installed on a concrete base with a mortared setting-bed and joints, as sand joints do not provide enough rigidity and cause the units to shift and crack. Brick is best used in residential landscapes or commercial areas in non-vehicular applications.

Concrete
Concrete in all its forms may be coloured integrally (with pigment present throughout the full depth of the material) or with a surface coating (pigment present only in the outer/upper layers of the material). Integrally coloured concrete has pigment added to the concrete mixture before it is poured, and the available colour range tends to be more subdued than with surface applications. Through mixing bags of standard colours, a range of custom colours can be achieved.

Surface coating applications are achieved by applying a layer of powdered colour hardener atop freshly poured concrete. While this application method provides a more uniform appearance and a more vivid palette of available colours, it should always be backed by a solid integral colour, even at an added cost. Concrete in our northern climate inevitably chips; thus, providing an integral colour beneath a surface application provides a longer life cycle by ensuring that chips and cracks do not reveal the grey concrete beneath.

While certain pigments—most notably reds and purples—perform notoriously poorly when added to concrete, there are a few preemptive strategies that can increase the longevity of coloured concrete applications. One option is to specify a darker colour than is initially intended, because it will fade over time. Another is to specify a higher “colour-loading” of the concrete mix–for example, two bags of the desired pigment per cubic volume instead of one. As with all poured-in-place concrete applications, the installation, curing, and finishing techniques used are critical to the longevity of the surface. For both integrally and surface-applied coloured concrete, manufacturers recommended regular coatings of a surface-sealing product.

Precast-concrete unit pavers face some of the same problems of discolouration and fading as poured-in-place applications; however, as they are manufactured in a controlled environment, they tend to be more uniform in finish, colour, and strength. The most commonly available colours are similar to those available for integrally coloured poured concrete; however, the sizes and textures available with precast pavers offer the designer a wide array of potential solutions.

Rubberized Surfacing
Rubberized surfacing, most commonly used in safety surfacing applications, is a combination of synthetic rubber and resin applied atop an existing surface. It does not conduct heat, is UV stable, and can withstand even harsh winter conditions. Products come in a wide range of colours, from earth tones to vibrant neons, and many manufacturers offer custom paving patterns. Two main factors affect the colour steadfastness of this material: the concentration of synthetic rubber (made of ethylene propylene diene terpolymer or EPDM) and the quality of the binding resin. Products with a lower concentration of EPDM require more fillers, which break down in high UV, reducing the lifespan of the product.

When choosing rubberized surfacing, it is important to specify a manufacturer whose product has integral colour in each rubber granule as well as a high concentration of EPDM, as this allows the product to have a remarkable lifespan in both colour and durability. Clients can expect only a 10-percent colour fade over a span of 20 years. Given the longevity of rubberized surfacing applications, it is of particular importance to specify the colour and paving pattern wisely.

While this material is extremely durable, it must be installed properly in order to last. And while it has a lifespan twice that of concrete, its application opportunities are limited mainly to playground areas requiring play safety surfacing. However, its ability to reduce fall injuries makes it an interesting product to consider in the design of trail systems, care and rehabilitation facilities, and seniors housing.

In Conclusion
While each of the products discussed performs differently in the landscape over time, one common consideration is the importance of proper base assembly and installation in ensuring the long-term success of any material. As well, identifying the right product for the right place is key. Is the space residential or commercial? Will the paved surface need to withstand vehicular traffic or only pedestrian traffic? These initial questions will help the designer hone in on the optimal paving solution for the project.

Designing with colour can also become less daunting if we understand the materials and communicate to our clients that all colours change over time. As with all coloured products, earth tones have slightly longer colour steadfastness than bright colours. We can adjust for these known variations in the design phase through careful selection of colours and materials, and by avoiding those which we know have poor success rates. Employing design strategies that combine timeless colours with more vibrant hues in select areas can also extend the product’s sustainability on a project. By advocating for what we know will perform well over time, we can avoid “cat food pink” while still bringing a bit of colour to the ground plane.

BIO/
NADJA PAUSCH IS A MEMBER OF THE GROUND EDITORIAL BOARD AND A LANDSCAPE DESIGNER WITH FORREC LTD.