4.4.3. Application Process

For rough surfaces, a slurry of cement is dashed on to improve bond.

The dashing coat is the first step in the plaster application process for uneven surfaces. It involves taking a mixture of cement and water to create a slurry. This slurry is then forcibly thrown or 'dashed' onto the wall surface. The purpose of this step is to create a rough texture that allows the subsequent layers of plaster to adhere better. Essentially, it acts like a base layer that holds everything together.

Imagine putting glue on a piece of paper before sticking another piece of paper on top. If the surface is smooth, the glue may not hold well. But if the surface is textured, like crinkled paper, the glue sticks better. The dashing coat works in a similar fashion.

10–12 mm thick. Scored with horizontal lines for better adhesion.

The first coat, also known as the scratch coat, is applied next and is about 10 to 12 mm thick. After applying this coat, workers create horizontal lines or grooves across the surface using a scratch tool. These grooves help to create a mechanical bond with the next layer of plaster. The scratch coat is essential because it adds depth and support to the finish, ensuring that it stays intact over time.

Think of the scratch coat like the rough surface of Velcro. When you press two pieces together, the hooks and loops mesh firmly, creating a strong bond. In the same vein, the grooves in the scratch coat help the next layer of plaster stick much better.

5–8 mm thick. Applied after initial coat sets; levels and flattens the surface.

The second coat, known as the brown coat, is applied after the first coat has set or dried partially. This layer is thinner, measuring about 5 to 8 mm thick. The primary purpose of the brown coat is to level out the surface and fill in any imperfections left by the scratch coat, pushing the plaster into the grooves to create a smooth finish. This coat is crucial for achieving a uniform texture and preparing the surface for the finishing details.

Imagine a sculptor working on a statue where the first rough shape is formed with large chunks of material. The second step would be for the sculptor to smooth out and refine those rough areas, ensuring a beautiful finish. The brown coat is like this second step of refinement, taking the roughness out of the wall.

2–3 mm. Applied for aesthetics and smoothness.

The final coat, or finishing coat, is the last layer of plaster applied to the wall. This coat is much thinner than the first two, typically between 2 to 3 mm thick. The purpose of the finishing coat is to provide aesthetic appeal, offering a smooth surface for painting or decorative finishes. This layer is applied after the brown coat has set properly, ensuring that the entire surface looks uniform and attractive.

Think of icing on a cake. After baking and assembling the cake layers, the icing is the final touch that makes the cake look beautiful and delicious. Similarly, the finishing coat is what gives the wall its final polished appearance, ready for decoration.

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