In a stucco project, after you have applied a scratch coat to your surface, there are some basic guidelines to follow before applying a brown coat. While timing will vary by project, this should be used as a basic guide.
Applying Scratch Coat
After you have applied your scratch coat to a uniform thickness all over your surface, you will immediately want to “scratch” the surface horizontally to create a better surface for the next coat—the brown coat—to bond to the surface. After scoring the surface, it is best to let the surface cure for 10 to 12 hours to make sure it has solidified.
After waiting for this amount of time, apply a gentle stream of water to hydrate the scratch coat. Once this moisture has absorbed, continue to hydrate the wall for the next 48 to 72 hours until the surface stops absorbing water.
Applying Brown Coat
Once you have properly hydrated the scratch coat to the point where it is no longer absorbing the moisture being sprayed on it, you will be ready to apply your brown coat. After mixing the brown coat, allow it to sit for 20 minutes or so before applying it to the moist surface of the scratch coat.