A sandstone retaining wall is a popular choice for landscaping due to its natural beauty and structural strength. However, without proper drainage, these walls can fail under hydrostatic pressure. This is where drainage aggregate plays a critical role.

Why Drainage Aggregate Matters

Water trapped behind a retaining wall builds pressure that can crack or push the sandstone blocks out of alignment. Drainage aggregate allows water to flow freely away from the wall, reducing pressure and preventing soil erosion. It also helps keep the backfill dry, which preserves the integrity of the sandstone.

Best Aggregate for Sandstone Walls

Crushed stone or gravel between ¾ inch and 1½ inches in size works best. Rounded pea gravel is less effective because it compacts over time, reducing permeability. Angular crushed limestone or granite provides superior void space for water flow. Avoid using sand or fine materials, which clog drainage paths.

Installation Tips

First, dig a trench behind the wall and line it with geotextile fabric. Then place a perforated drainage pipe at the base, surrounded by at least 12 inches of clean drainage aggregate. Cover the pipe with more aggregate to the height of the wall, folding the fabric over the top to prevent soil intrusion. Include a minimum of one weep hole per 10 square feet of wall face to release water.

Additional Considerations

Always install a waterproof membrane on the wall’s backside to protect the sandstone from moisture damage. Ensure the aggregate extends above the highest water level expected. For taller walls, consult an engineer to calculate precise drainage requirements.

Proper drainage aggregate is not optional—it is the key to a sandstone retaining wall that stands strong through rain, frost, and time. Choose the right material, install it carefully, and enjoy a durable, beautiful wall for decades.