Leaking Pond Liner Seam: Repair or Replace?

Leak at the seam joining two liners? Repairing in situ is risky. Here's the professional reality.

Liner Type Determines Options

Why Pros Don't Join Old to New Liners

• Old liner is dirty, wrinkled, contaminated with biofilm.
• Underwater cure environment = guaranteed failure points.
• Mud, roots, movement prevent proper adhesion.
• Hours of labor + materials at risk for a joint that will leak.

Professional Alternatives

1. Flow new pond into old: Separate liners, connected by stream/waterfall. No seam underwater.
2. Remove old liner, install single-piece new liner: Only reliable long-term fix.
3. Build above-ground section with separate liner, plumbed to main pond.

If You Must Attempt EPDM Seam Repair

1. Drain to below seam.
2. Dry area completely (heat gun/torches—carefully).
3. Scrub with acetone, then alcohol. Let flash off.
4. Apply lap cement to both surfaces, let tack.
5. Roll seam tape with heavy roller.
6. Weight seam 24 hrs before refilling.
7. Expect 50/50 success rate.

Bottom Line

In-place seam repair is a gamble. Single-piece liner or separate connected ponds are the only reliable designs. Don't risk your fish on a questionable patch.