Application of the Coats
Now the messy fun starts! A scratch coat is applied to the metal lath with a trowel. It consists of cement, plaster sand and water. Texture and consistency are critical here and experience makes all the difference. Once in place the surface is scored or scratched with horizontal lines, hence the name ‘scratch coat’. The scoring leaves a textured surface that gives the second coat something to hang onto.
The scratch coat is then wet cured. Wet curing is a process by which the scratch coat, is allowed to set but kept damp at the same time to prevent it from drying too rapidly. Adding water to the cement when it is initially mixed sets off a chemical reaction called hydration. The extra water during the curing process allows the cement particles to create a good bond with the surrounding aggregate and other cement particles. This is how the cement hardens properly.
After the scratch coat has cured sufficiently the brown coat is mixed and applied. While its’ composition is similar to the scratch coat the finished product is very different. The brown coat is much smoother than the scratch coat. Although it has a gritty feel, it is flatter and more attractive than the scratch coat. Since it is a uniform surface it is the perfect base for your stucco. The brown coat must also be wet cured but for a much longer period than the scratch coat.