liners are the most expensive piece of the pond puzzle, so you don't want to
make any mistakes. Do some simple calculations to figure the size of the liner
you need. Measure the length of the pond + twice the maximum depth.
Then measure the width of the pond + twice the maximum depth. Also allow
for a 1-2 foot overlap. It's better to have too much liner than too
little, so if in doubt, go with more rather than less. Then add the two
numbers together to calculate the total liner you will need. Don't forget
to add whatever you will need to cover the waterfall spillway if your design
calls for that. You can use scrap for this, but just be sure you have
Example: If you have a 10 foot long x 6 foot wide pond that is 2 feet deep at the deepest point, the calculation would look like this:
6 (width) + 2 (depth) + 2 (depth) + 2 (overlap) = 12 feet in length
10 (length) + 2 (depth) + 2 (depth) + 2 (overlap) = 16 feet in width
Your liner would be 12 x 16
When purchasing your pond liner, do so carefully and read the fine print. Basically, flexible liners are either rubber or plastic. Rubber is far superior but costs more. The liner pictured above is a rubber liner. It was 20 x 20 and cost about $400. I put a plastic liner guaranteed for 10 years in my in-ground pond, and it lasted about 4 years before I started noticing serious degradation around the edges. I eventually had to rebuild the whole pond. Bad mistake. Make sure your pond liner is guaranteed for 20 years minimum unless you just want to rebuild every 10 years or so. If there is a store around that specializes in ponds, buy from there. They are knowledgeable and will sell you a quality liner. The big home outlets such as Home Depot and Lowes will usually not have the highest quality liners available, as they are geared towards smaller pond installations. However, if yours is a smaller pond that's not too involved and cost is a factor, then a liner from the home outlet may be adequate for your needs.
Here's a list of pond liner terms that will come in handy:
ML - Thickness of pond liners are shown in mils. 1 ml equals 1/1000 of an inch or 1/40 of a millimeter. A 30 ml EPDM rubber liner is a good all-around choice for smaller free-form ponds with a lot of twists and turns, especially if you are on a tight budget. It is flexible and easy to handle. For larger ponds with rubber liners, 40 ml and even 45 ml will work well and last for years. Synthetic plastic liners are usually sold in 20-40 mil thicknesses for home use. 40 is better but 20 or 30 may be just fine in some instances.
EPDM - Ethylene-Propylene-Diene Monomer: This is an industrial grade rubber available in varying thicknesses, and is the best bet for most all pond installations, but is also the most expensive option. It is flexible and easy to work with, and conforms nicely even when twists and turns are involved in the pond installation.
HDPE - High density polyethylene - This is a heavy duty synthetic plastic liner sold in 20-40 ml and up thicknesses for home pond use. It is a bit less expensive than rubber liner, molds nicely to tight corners, and usually comes with a 20 year guarantee. In some situations, especially large ponds that need to be done economically, this is a good choice.
PVC - Poly Vinyl Chloride: Synthetic plastic liner. This is a budget liner and is the one that you will probably find at the local home center. It usually comes in 20-40 ml thicknesses and will mold nicely around twists and curves. PVC liners come with a 10-20 year warranty for perfect conditions, but are definitely not as durable as rubber or even HDPE.
UV Stabilizer - Make sure your liner says that it is made with a UV stabilizer or it will fall apart within a few years in sunlight. Unless you are sure that no part of your liner will see the light of day, make sure any pond liner you choose has this feature.
Fish Safe - Always be sure that the pond liner you buy has a "fish safe" guarantee. The manufacturing process for fish safe pond liners is different than for other uses, and some liners that at first glance look like they could work well in a pond will emit gasses and chemicals that are fatal to fish. For instance, if you know someone who does roofing work, they might come across some roofing liner that looks like it would work for your pond. Do not use this, because it will almost surely kill anything you put in that pond.
Rigid ponds - Prefab ponds come in fiberglass and plastic, with fiberglass being the more expensive and more durable of the two. If the prefab is going to be situated with any side out of the ground and unsupported, go for fiberglass because plastic will eventually crack. If doing the prefab completely in-ground, plastic is fine.
Ok, having said all that, the first thing when you get that flexible liner is find someone to help you haul to where the pond is going to be. That little square package looks innocent, but it's going to be heavy. The UPS man will curse you for days if you order over the internet. Find a big place in the yard to spread it out. You want to make it malleable and easy to place in the pond without too many wrinkles. It helps to do it on a sunny, warm day. It doesn't matter if it gets a little dirty. Pond scum will ugly it up in a hurry anyway. Also, have enough blankets, sand, comforters, or pond pad on hand to line the bottom of the pond. Anything will do as long as you pad the bottom to protect from tree roots, sharp stones and the like. Spread the liner over the hole, smoothing it out as much as possible, and not forgetting to line the waterfall spillway while you're out there, if applicable. Once you have smoothed it out as well as possible, you can finally fill it and see the results of your labor.
If you have a prefab pond, turn it upside down where you want it, draw an outline with talc or paint or whatever you have around, and then dig down along the outline a little deeper and a few inches wider than the pond will sit, making sure to clear all debris from the hole. Pour sand into the hole for a pad and to make leveling the pond easier. Fill slowly with water while backfilling the excavated soil around the edges of the pond, making sure to tamp down for good side support.
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