How to Waterproof a Planter Wall

Clean all dirt and debris from the inside of the planter wall and allow it to dry thoroughly.

Brush water-based bitumen paint over the inside surface of the planter, keeping the brush strokes aligned in one direction. Allow the paint to dry for 30 minutes

Apply a second coat of paint. Brush it on in a direction perpendicular to the first coat, forming a 90-degree angle to the first set of brush strokes.

Wait seven days after applying the second coat of paint before filling the planter with dirt or potting material.