Concrete liners typically require an underlayment to ensure proper installation and enhance their performance. The underlayment helps provide a stable, smooth surface for the concrete, preventing uneven settling that could lead to cracks or shifts in the liner over time. Materials like geotextile fabrics or compacted soil are commonly used as underlayments.
Geotextile fabrics help to filter water and prevent the migration of fine particles into the concrete, which can weaken its structure. In some cases, a layer of sand or gravel may be used to provide drainage and reduce hydrostatic pressure beneath the concrete, which can otherwise cause damage.
