Step 1 - Choosing a Pond Liner

One of the most important decisions in pond construction is choosing the right liner for your specific project. The most common pond liners include EPDM, PVC, bentonite clay, concrete and my choice, polyethylene. All liners have advantages and disadvantages. I’ll talk about all of them in detail.

I tend to over think things. This certainly was the case when it came to choosing a pond liner. I like a natural looking pond and hate the sight of an exposed liner.  There are several factors to keep in mind when choosing a pond liner. My biggest concern with an artificial pond liner was leaking. This is why my first choice was to use bentonite clay. It didn’t work.

Bentonite Clay

Over the last several years, bentonite clay has gotten recognition as a ‘bulletproof ‘ alternative to a synthetic pond liner. There are two types of bentonite clay available, sodium and calcium. It’s important to use the correct kind of bentonite for pond sealing. Sodium bentonite is the way to go. Calcium bentonite is the stuff they use for kitty litter and it isn’t going to work. The basic concept is to mix the bentonite with the natural soil to create an impenetrable barrier. It seemed simple enough.

Choosing a pond liner | Natural Pond Lover
The bentonite clay disaster.

Soil type matters

We have sandy soil here in Florida. This soil type needs more bentonite than a more dense soil would. So, I performed the bentonite soil test. Do this by taking a five-gallon plastic bucket and drilling 25 holes in the bottom. The next order of business is to add three or four inches of native soil to the bucket. 

Next, add the bentonite clay. I continued adding the granules until the water no longer leaked out of the holes from the bottom of the bucket. After a couple of cups of bentonite clay, absolutely no water escaped. Alright!

With only positive thoughts, the clay barrier seemed successful. Next, it was time to add the bentonite to the pond itself. It turned out an absolute disaster. According to my calculations, I had bought thirty-six bags of bentonite at fifty pounds each. Meticulously, I tilled the bentonite into the soil. After several hours I was ready to add water and the pond filled up overnight. The next morning it appeared successful. Turning the water off, I triumphantly returned to my day job.

The first sign of trouble

Some hours later, I returned only to find that the water had gone down dramatically. I tried to refill it again. The same result, only this time the water couldn’t even make it to the top of the grade. As a last desperate attempt to save the project, I added some extra bags of bentonite that I kept for possible leaks down the road. I then dumped the clay granules directly over the surface of the soil. Still no good. What’s more, I noticed that once the water level went down, the clay dried out and large cracks developed. Some of them were as wide as two inches.

Failure is a tough pill to swallow

Bentonite was certainly not a bulletproof pond membrane in my situation. The worst part was trying to dig the clay back out to salvage the job. The idea of using an artificial liner suddenly appealed to me. In trying to excavate the clay, I ended up throwing my back out. My left elbow was also screwed up which was making a cracking sound every time I bent my arm. It took almost a year to heal.

Physically injured and defeated, I decided to hire a professional pond contractor. That turned out an even worse idea than the clay.

My experience with bentonite clay was unsuccessful. This was probably due to the sandy soil conditions. A denser soil type could be more effective with bentonite clay. I wouldn’t recommend it in Florida when choosing a pond liner. It would probably take a barrier of at least twelve to fourteen inches of bentonite for sandy soil. That simply isn’t possible in my situation. I don’t recommend it for such soil types.

Fall | Natural Pond Lover

Remember 

Even if your native soil is thicker and the bentonite seal is successful, always keep the pond topped off and completely full. During a drought, the water will evaporate causing large cracks to occur. These cracks need re-sealing. I can’t imagine that being a very fun task.

PVC

Good ‘Ol PVC liner, the kind readily available at your local home improvement center at a reasonable price. I’ll bet you’re thinking I’m going to bash PVC. On the contrary, I actually have good things to say about it. At the present time, I have no ponds lined with PVC, however, I once had three of them. First of all, PVC has come a long way over the years. The kind I used had fabric woven into the plastic making it more durable. Still, you’re going to need a good underlayment. It bends very easily making it the best liner for curves and bends in the pond’s structure. It’s also very light compared to the other liners.

So, why do I no longer work with it?

First, I wouldn’t recommend it for large projects. They don’t make PVC liners that big anyway. The second reason is it seemed like water wasn’t holding as well as it should. I wouldn’t recommend it for larger projects but perhaps smaller ponds.

The liner won’t last as long as EPDM, or polyethylene. If I had no other choice and had to use PVC, I would use a good underlayment. PVC is cheap, so I would double the liners (use two of them) for added protection and durability. The problem with doubling liners is that you’ll have more creases and folds.

EPDM

EPDM is the most popular choice when choosing a pond liner. This membrane is rubber and not plastic (PVC, polyethylene). One of my six ponds that I lovingly refer to as ‘the lagoon’, uses an EPDM liner. The lagoon is sixteen feet long. It was hard to lay that heavy liner by myself.

I believe Firestone manufactures EPDM specifically. You can also get it at roofing supply stores but it’s ill-advised. These liners are often contaminated with fire retardants and other harmful chemicals. It’s best to buy EPDM specifically designed for ponds. You should still clean it before installation.

Most pond contractors install EPDM exclusively. 45mil is the industry standard but you can ask for the thicker 60mil liner. Does thickness really matter? Maybe in certain situations. If a raccoon gets to the liner, the extra thickness won’t matter. Of course, the thicker the EPDM, the more expensive it is.

The heaviest of pond liners

EPDM is the heaviest of pond liners. That doesn’t necessarily make it the strongest. When installed correctly, EPDM lasts a long time. It wraps around curves but you can expect major creases and folds. Ideally, keep curves limited during construction for this reason. Multiple curves also lead to oxygen deprivation. Uncovered folds at the waterline stick out like a sore thumb. They are targets for raccoons and other destructive animals.

Out of my six ponds, only one uses EPDM. Why is that?

I had a bad experience with EPDM the first time around. It wasn’t installed correctly by the ‘professional’ pond contractor I hired. I can assure you that raccoons and similar animals can chew right through a 60mil EPDM liner. When I installed it myself the right way, I had success with EPDM.

The only two negative points I can come up with on EPDM is that it’s the heaviest and most expensive of the pond liners. It’s also more difficult to install if you have no one to help. If you’re building a really large pond or even a lake, EPDM isn’t possible. I tend to prefer bigger projects. Still, I would use it over PVC, concrete or clay making it my second choice. I do enjoy my pond with the EPDM liner but I think it’s best for garden ponds.

My preferred pond liner – Polyethylene

When choosing a pond liner, polyethylene is my first choice. Polyethylene has changed a lot over the years while EPDM hasn’t. It’s very durable and now the strongest of all liners. It’s also light, at least lighter than EPDM. Folds and creases around sharp bends still occur with this liner. It’s often said that polyethylene is so strong that you won’t need an underlayment. I still recommend one for added protection

The price of polyethylene is extremely reasonable. It’s easy to patch up with a specific kind of tape and it’s UV resistant. Still, never have any exposed pond liner. Polyethylene comes in different thicknesses. I prefer the thickest, which is 40mil. Large pieces are welded together the liner is created to your specific needs. Last but not least, it’s the only commercially available synthetic liner that comes large enough for large ponds and lakes.

One last thought on EPDM

I’m not completely throwing EPDM under the bus here. You can still use it in certain situations with great success and it’s still my second choice. In Florida, we never have a hard freeze that lasts more than a couple of hours. I’m not sure how polyethylene reacts to below-freezing temperatures, so I recommend burying this liner below the frost line.

Polyethylene is the way to go

So there it is. My personal favorite of all pond liners. If I ever build another pond, it will be with polyethylene. What it boils down to is the size of the project because EPDM and PVC have limitations.

Underlayment

Don’t forget the underlayment when choosing a pond liner. An underlayment is always a good idea. While it doesn’t make a pond ‘bulletproof’, it helps. An underlayment reduces the weight of the water when the liner presses up against stones, rocks, roots, and other sharp and potentially damaging objects. Commercially available underlayment is usually made of fabric. You could also use old rugs. While some people use newspaper, I wouldn’t recommend it because it breaks down too quickly.

Carpet Underlayment | Natural Pond Lover
Pieces of old carpeting are sometimes used as an underlayment. Carpeting and commercially available fabric underlayment are much better than using newspaper.

It’s worth getting a good underlayment because once that baby fills up with water, you’re not going to want to take it apart again. Trust me on that! Instead, spend time choosing plants and determining where you’d like to put them.

Why you shouldn’t consider a concrete pond

The first sealer I considered was concrete. The town I live in considers two liner types as a permanent body of water which is clay and concrete. We already talked about clay. Just because they consider concrete permanent doesn’t make it bulletproof.

First, concrete cracks. Especially here in Florida where it’s very common in such slabs. If a crack develops at the bottom of the pond, it needs to be completely drained in order to fix it. Secondly, it’s hard to create a functioning ecosystem due to concrete alkalinity. Beneficial bacteria doesn’t take well to concrete like it does rubber or plastic liners. Chronic cloudy water results which nothing can solve. Even if you seal it, it just takes a small missed spot. Most plants have a difficult time growing in concrete ponds.

The idea of having a concrete pond appealed to me because I thought it would be the least likely to give me problems. After learning more about it, I found it wasn’t the right way to go when choosing a pond liner.

Conclusion

After much research and experience, I’ve arrived at the conclusion that no synthetic pond liner is bulletproof. That’s okay. Why? Because ponds found in nature aren’t bulletproof either. It’s just the way it goes. Let’s start digging!

Choosing a Pond Liner