Do 3D Drop-In Liners require an underlayment?

Because of its high puncture resistance, this liner does not require a protective underlayment when installed over regular soil, sand, or clay. If the soil contains small rocks that are compacted and embedded in the ground, and the rocks are not sharp, an underlayment is still likely unnecessary. However, if there are any loose rocks or debris, we recommend compacting the material into the ground or raking it out so that no loose material remains beneath the liner.

When installing the liner over an abrasive surface such as granite or concrete, a protective underlayment should be used to prevent wear and abrasion. If your substrate contains sharp rocks, the best approach is to fill the area with sand or soil to eliminate any chance of sharp objects coming into contact with the liner. The water will exert hundreds or even thousands of pounds of pressure against the surface, so it is essential to ensure there is nothing sharp pressing against the liner.