Commonly used for driveways, and around pools, exposed aggregate includes decorative elements such as pebbles, stones, coloured glass, shells or other materials set within concrete producing decorative and hardy surfaces. These aggregates can be added to the concrete in several different ways.
1. Integral Mix
One way is to pre-mix the decorative bits within the cement before it is laid. Because the aggregates are evenly dispersed throughout the entire cement mix, and not just across the surface, this can be more expensive than other methods that use less aggregate material overall. One thing to consider with this method is the strength of the solid concrete, bearing in mind that the aggregate elements are scattered throughout. Depending on the amount and specific type of aggregates, the concrete could strengthen or weaken.
2. Topping Aggregate
Another method is to again pre-mix the aggregate elements into a cement composite, but in this case, only a thin layer of the decorative aggregated cement is laid over an existing base slab of standard concrete. Because the decorative pieces are just embedded within the thinner top layer and not the base layer, you will need less decorative material overall. For a similar decorative effect, this process can be more cost-effective than the integral method which uses more embellishments.
A third method is to lay conventional concrete and then, while it remains unset, to insert the beautifying aggregates into the mixture. Depending on the design, the elements can be sprinkled over the top with shovels or by hand and then embedded within, so a thin layer of cement covers them. This option provides more artistic control over the finished look as the decorative elements are manually added after the concrete is laid and the functional part of the process is taken care of.
Constant in all three methods, after the laying is complete, the aggregates are covered with a thin layer of cement. This is later removed by particular processes to reveal the embedded pieces within.
Which of these methods you choose depends on your design goals and cost factors. Adding aggregate material only to a top layer, rather than throughout the concrete, requires fewer aggregates. Seeding also requires fewer aggregates, but it does involve specific manual labour to place and design the arrangement, providing ultimate artistic control over the final effect. Though the integral method of premixing all the cement and aggregates uses the most decorative bits, it is the most straightforward.