Everything You Wanted to Know About Pond Liner, but Were Afraid to Ask

Here is the deal with Pond Liner

If you want the simplest pond around you can dig a hole and fill it with water:  POOF!  Instant Pond!

Then, once all  the water has  seeped into the ground you will realize that you need something more.

There are four ways of keeping the water contained in your pond.  Rigid liners, Rubber or Plastic Flexible Liner, Concrete, or Sodium Bentonite Clay.  Bentonite Clay is generally only used for very large water features, and only for those features that have a very regular source of water (such as a stream, spring, or well) since the clay still allows a certain amount of seepage.  Concrete is the preferred method of many pond and pool builders, but it has a few drawbacks.  Mainly that it eventually cracks (especially in regions that have regular freeze/thaw cycles) and leaks, but it also can be expensive and difficult for the average builder to work with.  Rigid liners have their place, since they are portable, easy to set up, and will usually stand up on their own, but overall they are expensive (due to the plastics used and shipping costs), difficult to disguise, and usually can’t handle much weight set on the sides without splitting.   They also are a pain to repair when they split.

That leaves liner.  It is usually the most practical means of containing pond water for your average pond.  It’s relatively cheap, reliable, easy to work with , and allows you to be very flexible in your pond design.  It’s only real drawback is that it does require a certain amount of care when installing or maintaining to prevent holes.  You can walk on it, even with your shoes, and if you use the recommended underlayment it can be reasonably difficult to puncture, but it can be easy to slice.  Always be especially careful not to drag rocks, your feet, rakes, or whatever across the liner.  The good news is that liner is easy to repair, but the bad news is finding a hole can be a real pain in the.

Liner comes in a variety of types and thicknesses.  Polyethylene, PVC, and EPDM liner are usually available, and each has it’s practical purposes, but currently the most popular liner for backyard pond building is a 45 mil thickness EPDM  (ethylene propylene diene monomer, if you care).  EPDM liner is flexible, durable and heavy, at about 1/3 lb per square foot.  It can easily be seamed or repaired right on-site using a special primer and either a single or double sided seaming tape.

Again, this is POND LINER we are talking about, not roofing liner, or greenhouse plastic or any other weird sheets of plastic that some people try to get away with.  Roofing liner has fire retardants, fungicides and other chemicals in it that can be toxic to aquatic life, and greenhouse plastic won’t last much longer than just digging a hole and filling it with water.  It’s tempting to try and save a buck, and that is understandable, but don’t do it on the liner or you will regret it later.

Finding the liner size for your water feature is simple (although it may not sound simple from my explanation).  Measure the widest width, the longest length and the deepest depth.   When you install the liner it will go down one side of the hole and up the other side, so you have to take two times the depth and add it to the widest width, then you take two times the depth and add it it the longest length.  That will give you the width and length of the  liner you need from one edge of the pond to the next, but you also will want extra to go under the rocks, or whatever edging you are going to place around the sides to hold the liner in place.  The amount of extra liner you get depends on what you are doing around the sides of the pond, but usually I recommend an absolute bare minimum of 1′ of extra liner on each side.  More is better, since it’s better to have extra than not enough.  So, at the very least your formula would be, in feet:

Widest Width of excavation +  (2 x Deepest Depth) + 2 feet = your liner width

Longest Length + (2x Deepest Depth) +2 feet = your liner length

Alternately, you can take a string and run it from one edge, down through the pond, to the other edge and then measure the string, but don’t forget to add the extra overlap on the sides.

Before you install the liner it is recommended by almost all manufacturers and pretty much anyone who has installed a pond before that you lay down an appropriate underlayment.  An underlayment is a fabric that goes underneath the liner and protects it from any sharp or rough objects from below.  Most liner manufacturers recommend a nonwoven geotextile underlayment in either a 6 or 8 oz thickness.  This underlayment moves with the liner and will actually keep the liner from stretching, and thereby make it much more difficult to penetrate the liner with sharp objects from both beneath the liner and from above.   Some people like to use carpet scraps, old blankets, burlap and other things.  These are better than nothing, but the geotextile underlayment is not all that expensive so why would you want to scrimp on something that can save you so many headaches later?

Also, remember you may want extra liner to run up your waterfall or stream if you are going to build one.  Ideally you would use a single sheet of liner for the entire project, but sometimes that just isn’t practical, so it is possible to use two separate sheets for each.  I will cover options and techniques for that in a later blog, along with methods of adding bottoms drains, through fittings, bulkhead fittings, pipe boots, and other liner perforations as well as liner repair.  I can also cover concrete, and natural bottom pond construction and repair.

If you wish to see more information and some instructional videos I recommend visiting the website for Firestone PondGuard Pond Liner at www.FirestoneSP.com.


Up Next: Water Feature Selection & Design, Excavation, Installing the liner, Pump Selection, Pond Filtration

(I didn’t intend to write a book, but it seems to be going that way)

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