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  • Writer's pictureCory Grant

Integral Colour in Exposed Aggregate Concrete and Different Coloured Aggregates

Updated: May 26, 2023

Exposed aggregate concrete, a very popular decorative concrete finish, gets its appearance and texture from aggregates within the concrete mix, which can include materials like crushed rocks, small stones, pebbles and sand. The simplest way to achieve this finish is by washing and brushing off the cement paste until the aggregates are revealed. In a different method, the aggregates are broadcast over wet concrete and embedded before the concrete sets. This is followed by the same washing and scrubbing techniques to expose the aggregates. Selecting Coloured Stone Aggregates

In exposed aggregate finish, the final dominant colour of the surface will rely on the colour of the stones while their size and shape will determine the surface texture. Stones, known as coarse aggregates, are available in an amazing spectrum of colours such as marble, green or black quartz, feldspar, obsidian, red gravel, granite and basalt, just to name a few. The variations in colour of these natural stones depend on their geological source. With the wide colour selection, it is easy to choose colours that will enhance any landscape. If you want a light exposed surface, you can choose stones in subtle pastels like rose quartz. For earthy tones, some options are grey limestone or black basalt. If richer tones are desired, there's dark blue granite or red lava rock. Frosted rose river rock and cranberry granite are other interesting options.

Aside from the colour, however, there are other factors to be considered in selecting decorative coarse aggregates such as size, grading, shape, surface texture, and durability. All of these things should be taken into consideration to ensure the chosen aggregates would be appropriate for the intended use. For example, it is best to use smaller stones that are easy on the feet for pavements that receive barefoot traffic like in pool areas while smooth, glassy stones may not be suitable for sloping footpaths because of their low skid resistance.

Colouring the Concrete

While the coarse aggregates impart their natural colour to the concrete's surface, the cement matrix in between them can also be coloured so it's not just plain grey or white. One way to colour concrete is to use integral colours, which colours the concrete throughout. These pigments are called integral because they are mixed into the concrete mix, resulting to a colour that is carried all the way through the concrete.

The use of integral colours is more convenient than other colouring options since the colour is already mixed into the concrete. This is also means savings in labour costs because no extra steps to colour the concrete are required; the concrete can be placed and finished as normal. Also, because the colour is integral to the concrete, it is will not peel off even if the surface is chipped.

In choosing an integral colour, select a shade that will complement or enhance the colour palette of the coarse aggregates. The correct pigment proportion is important to get the desired colour and pigment suppliers will be able to help in determining this. It is essential to do small test samples to find out the exact pigment and level of concentration that should be used.

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