The different finishing techniques applied on exposed aggregate concrete play a crucial role in defining the final appearance and texture of its surface. It can make or break the whole aesthetic of the project depending on the look you wish to achieve. We have touched on a few of these techniques in our exposed aggregate concrete guide but we thought we’d get into a more detailed view of each technique and how they can bring your exposed aggregate concrete to life.
Let’s get to it!
One of the oldest and most traditional methods for finishing exposed aggregate concrete is the brushing and washing technique. This method involves removing the top layer of cement paste to reveal the aggregate beneath. The process starts once the concrete has been laid and begins to set but is still malleable. A stiff-bristled broom is used to gently brush the surface, followed by washing with water to expose the aggregate.
The key to success with this technique lies in timing; starting too early can dislodge the aggregate while starting too late can make it difficult to remove the cement paste. It’s a delicate balance that requires experience and a keen eye for detail.
Chemical surface retarders offer a more controlled approach to exposing aggregate. Applied to the surface of freshly poured concrete, these retarders delay the setting of the cement paste on the top layer while allowing the concrete beneath to harden as normal. After a specified period, usually 12 to 24 hours, the retarded paste can be washed or brushed away, revealing the aggregate.
The depth of exposure can be adjusted based on the type of retarder used and the application method. This technique is particularly useful for larger projects or intricate designs where precision is key.
Abrasive blasting, including methods like sandblasting and shot blasting, is used to expose the aggregate after the concrete has fully set and hardened. This technique involves blasting the surface with a high-pressure air and abrasive mixture to erode the cement paste.
While effective, abrasive blasting requires careful execution as it can potentially damage the aggregate and affect the overall texture of the surface. It’s often used for achieving a more rugged, textured finish and is best handled by professionals with the right equipment and expertise.
Polishing is a finishing technique that transforms an exposed aggregate surface into a smooth, glossy finish. This method involves grinding the surface with progressively finer abrasives until the desired level of smoothness and shine is achieved. Polishing not only enhances its overall look but also adds a layer of protection to the surface.
It’s ideal for indoor applications or areas where a sleek, modern look is desired. The process requires specialized equipment like concrete grinders and diamond polishing pads and is generally more labour-intensive than other finishing methods.
Sealing is a crucial final step in the finishing process of exposed aggregate concrete. It helps protect the surface from stains, weathering, and wear and tear, while also enhancing its color and texture. While this isn’t a finishing technique, it’s worth noting that this step ensures that any technique you may have used will have a lasting effect on the concrete.
There are various types of sealers available, each offering different levels of gloss and protection. Water-based sealers are popular for their ease of application and low odour, while solvent-based sealers are known for their durability and high-gloss finish.
Ideally, when the concrete has set enough to prevent aggregate dislodgment but is still soft enough to remove the top layer of cement paste.
Generally, chemical retarders do not affect the colour of the aggregate. However, it’s important to choose a retarder that is compatible with the type of concrete and aggregate used.
It is effective but may not be suitable for delicate aggregates or when a smooth finish is desired. It’s best used for creating textured surfaces.
Resealing frequency depends on the type of sealer used and the level of exposure to traffic and weather. Generally, resealing every 2-3 years is recommended.
Yes, combining different techniques can create unique and creative finishes. However, it requires careful planning and execution to ensure a cohesive look.
The choice of finishing technique significantly impacts the final look and feel of an exposed aggregate concrete surface. From the traditional brushing and washing method to more modern approaches like chemical retarders and polishing, each technique offers its unique benefits and aesthetic appeal. Grasping the nuances of each technique may be different with everyone so if you’re having a hard time getting the finish you want, expert concreters are there to help you out.