Pond Liner – Seaming a Bigger Pond

Published on May 20, 2009

Make It Bigger 5

Since there’s an axiom that says, “once you have a pond, you’ll wish you had a larger one.” And since using a liner in the making of ponds has become a standard, there needed to be a foolproof way to seam an existing liner to a new liner for the greater goal of having a magnificent, bigger pond.


Sound good huh? Sound easy? Well it isn’t and to be completely honest before you read on or look any farther let me say that the liner-seaming job you are about to read about almost never happened. I’ve done a lot of pond construction and have heard of and seen liners seamed and it almost never works. I was convinced by this homeowner, Mark Hughes, to help him seam his liner. After I told him it was impossible and I didn’t want any part of the job he convinced me to help out by saying he would do all of the work and that all I had to do was give a little insight as to why it wouldn’t work at the job site and supply him with a truck load of expensive koi and equipment so…I happily agreed.


Before we could seam the liner we laid out the outline of the addition using an extension cord but you can use a garden hose or spray paint.



After we had the layout set we dug down 10˝ or 12˝ to form a plant shelf. At this time we exposed the edge of the existing liner to see what condition it was in along with looking for any holes or issues that might cause us a problem with the seaming.


After the plant shelf was done the rest of the pond was dug to roughly the shape and depth we wanted. Also at this time the water returns were put into place along with the bottom drain and skimmer unit.


It is at this point that I lack a few images of the actual seaming because the drying time of the C.I.M. rubber membrane (more on C.I.M. later) left me with my hands full but let me explain in the next few steps how we did it.


Clear all debris from the existing or “old” liners edge. That means everything: rocks, dirt, plants, etc.


Slide some heavy, wide boards under this liner area. We used several 2 x 12’s that were 16´ long, side-by-side to span the curve of the pond. This created a wide, flat work surface that would prove critical, it may be necessary to lower the water level slightly at this time to allow for an adequate amount of the old liner to have slack.


The old liner should lay on top of this temporary work surface.


It’s time to thoroughly clean both sides of the old liner. It will be necessary to clean a good 12 to 18˝ band the entire length of the area to be seamed. Remember, both sides! Use a stiff scrub brush with the pond water and add some elbow grease. If the edge of the liner is curved, you’ll need to cut (with scissors, box cutter, etc) a straight-line edge. Also remember in determining your straight edge that the liner seam should extend up out of the water and over the new ponds edge by 18 to 24˝ minimally. To clean underside of the liner, simply fold the liner back on itself … hence the benefit of making a nice wide work surface with several of those 2 x 12’s!


Now that the edge has been trimmed straight and that you’ve cleaned the years of dirt and grime off the liner, it’s time to clean it again. Only this time with Acetone.


Acetone is a marvelous solvent for cleaning … gets all the oil’s and leaves a clean, dry liner surface. Remember to do both sides. This will be a step that will be repeated often as we proceed.


Time to stretch out the “New” liner over the newly dugout pond addition. Be sure to give yourself a good 3 to 4´ of extra liner on the edge that is to be seamed.


You will be placing the old liner on top of the new liner. The underside of the old liner has been better protected from the elements of nature, i.e., the sun. It should be in a superior condition to the topside. At this time make sure that the straight edge of the new liner is aligned and parallel with the new cut straight edge of the old. If not, you can trim the old to make this so. Remember that both liners need to overlap by 12 to 18˝. Oh yes, clean the topside of the new liner with Acetone (most new liners have powder on them to prevent sticking and aid in unfolding).


Ok, here we go.


Fold back the old liner so that it’s out of the way of the new liner. Peel off one side of the protective paper and run the joining-two sided sticky tape (most tapes are 6˝ wide) the entire length of the area to be seamed. As a rule of thumb, put the edge of the joining tape at the edge of the new liner. Now, since we’d rather be safe than sorry, run another joining tape the same way along side the first. This will double the sticky area.


Peel off the remaining protective paper on the top of both joining tapes and fold back the old liner on to the exposed sticky tape. Now press hard. Heck, stand up and walk on it slowly and thoroughly. Now clean, again, the top surface of the seamed old and new liner area with Acetone.


Place the 6˝ wide Seam tape (this tape is sticky only on one side) halfway over the new and old liner overlap …3˝ will be on the old liner and 3˝ will be on the new. Now press down hard and walk on it as well


Next, take some sandpaper (100 grit or similar) and scuffup the top of the newly applied seam tape as well as several inches all around the tape on the liner. Sure, go ahead and clean with Acetone one final time.


Now it’s secret weapon time. Mix up the gallon can of C.I.M. www.cimindustries.com/CIM-polyurethane-coatings (which means you’ll need a paint mixing rod and a power hand drill). Simply pour the little bottle containing the catalyst into the gallon can of black goop and mix via the hand drill for 3 minutes. Yep, your arms are going to get tired. We suggest standing above the can with it held firmly between your feet … the C.I.M. will thicken causing the can to want to spin.


It’s now time to paint or goop on the C.I.M. over the entire scuffed-up, seamed area. Be liberal with it and work fast. C.I.M. will dry overnight to a tough, rubbery membrane. Ta Daa!


You’re done. Grab a hose and start filling. Oh, you can use the Acetone to clean your hands. We’ve used this simple, but multi-step process on our own pond for a 100% success rate. Meaning no leaks.


In the morning pull out the work surface boards and start putting the liner into the proper position. Always make sure to get the liner flat against the bottom and side surfaces. Now that you’ve got a bigger pond you can go out and get some bigger, more beautiful Japanese koi.


About the Author

Mark Bodycott – years ago on a whim I built a water garden in my backyard. I became more and more interested in ponds and water gardens, I was hooked! I went to a new store (at the time) Quality Koi to check it out. After spending some time at the store they offered me a part-time job. Cool right?


So there I was 28 years old thinking about a major career change while I netted Koi and backwashed filters. After working part-time the owner asked me to close my auto shop and manage the store full-time. This was a dream come true for me.


After several years and changes I started USA Koi and USAKOI.COM. I was the first person and only distributor to break Evolution Aqua’s Answer onto the scene in the USA. Now I have cut back my equipment sales and started to sell Koi almost exclusively. Here at USA Koi I have retail and wholesale Koi sales, Japan trips, direct shipments and many other services.


To compete in this Internet world, I try to offer the best customer service you can receive along with healthy quality Koi.



463 Fish Pond Road

Glassboro, NJ 08028

Phone: 856-881-7088

Fax: 856-881-7089


Kloubec Koi Farm

2 thoughts on “Pond Liner – Seaming a Bigger Pond”

  1. Great article Mark, I mostly agree but I would also consider using EPDM pond liner because it’s super flexible and very easy to use.

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