Flagstone Waterfall Construction: EPDM Liner Is Mandatory

Silicone-sealed flagstone waterfall leaks because mortar and silicone cannot reliably waterproof stone joints. The only solution: EPDM rubber liner underneath.

Why Joint Sealers Fail

• Stone joints are irregular and numerous
• Thermal expansion/contraction breaks seals
• Water pressure finds every pinhole
• No mortar or caulk bridges all gaps permanently

Correct Construction Method

1. Excavate and shape watercourse
2. Install EPDM rubber liner (heavy-duty, 45 mil minimum)
3. Liner must slope continuously toward pump
4. No low spots where water pools outside system
5. Place flagstone ON TOP of liner
6. Mortar/silicone now only for aesthetics/stability—not waterproofing

Key Principle

The liner IS the waterproofing. Stone is decorative. This applies to all lined water features: ponds, streams, waterfalls, fountains.

Result

Leak-proof, durable, repairable water feature that lasts decades.