Roughcasting, otherwise called pebbledashing, is a masonry technique used to coat exterior walls with a mixture of slaked lime, sand, cement and pebbles. The process takes several days. The supplies required for roughcasting are lime, sand, cement, pebbles, water, a sturdy mixing stick, two large buckets, a trowel, plastic sheeting and a large plastic bin.
- Mix the lime with water
Combine the lime with water and let the mixture sit in a bucket for 24 hours. Use the proportions indicated on the package of lime. The resulting compound is called slaked lime.
- Combine slaked lime, sand and cement
Pour one part slaked lime into another bucket, then add one part cement and six parts sand. Stir the mixture thoroughly. This combination is called the base coat.
- Apply the first layer of base coat
Use a trowel to cover the walls with the base coat. Run the bottom of the trowel over the base to create a smooth, even surface. Let it dry for an hour, then gouge it with the point of the trowel. Give the base coat 24 hours to dry.
- Prepare the pebbles
Prepare the pebbles while the base coat dries. Place them in a large plastic bin and rinse them with water. Pour the water out and let the pebbles dry.
- Mix and apply the second layer of base coat
Mix a second batch of the base coat and apply it over the first layer. Smooth it with the trowel.
- Throw the pebbles into the wet base coat
Cover the ground with plastic sheeting to protect the surrounding area. Set the bin of pebbles in front of the wall and throw handfuls of them into the wet base coat. Periodically gather fallen pebbles from the plastic sheeting and return them to the bin. Continue in this manner until the wall is covered with pebbles.
- Press the pebbles into the base medium
Use your hands or the bottom of your trowel to press the pebbles into the base. Give the wall 24 hours to dry.