If you're currently designing a sloped outdoor space, choosing your retaining wall material can be a tricky task. You can pick from a few different materials, including concrete, wood, or even a stone retaining wall, depending on the purpose and location of your wall. Rather than using a stain or a seal, a more durable option for retaining walls made of concrete would be to render them. Rendering a retaining wall is a process that has several benefits compared to staining or sealing. A seal has to be reapplied every 3 to 5 years, whereas rendering a wall should protect it for up to 30 years.