leak in pond liner seam

Question
We expanded our pond last year.  Now there is a leak where the 2 pond liners are joined.  What is the best way to repair this leak (using fish-safe materials)?

Answer
Tasha,

First I have to know what kind of liner you have.  

If it is EPDM, there is a commercially available seam tape and lap cement that will make the joint.

If it is vinyl it has to be heat welded.  (Generally not possible) but there is no glue that will stick to it.

Having said that, this is why in my years of installing hundreds of ponds, I've never tried to join a new liner to an old one.  We've always found some other way to accomplish what the customer wants.  Either flowing the new pond into and through the old pond, or taking up the old liner and replacing with a new one-piece liner.  By the time I considered the cleaning, the difficulty of straightening out the old liner, the muddy environment of working and trying to keep the joint clean, and the hours of time and materials at risk if it did leak, I was never confident enough to attempt a joint that was going to be underwater...and we build ponds every day.  

We have made dozens of joints.  Always in EPDM. Always with joint tape and cement.  Always scrubbing and cleaning first with Acetone or Alcohol.  And always on a parking lot where we could get it perfectly straight and where we could roll down the joint.

In a pond, in place, I just won't do it.  It's just too much to risk.


Good Luck,

John