Fiberglass pond liners are part of the 'preformed' family of pond liners in that they are purchased in a predetermined shape and size. As a pond liner, fiberglass is a very good material. It is tough, long lasting and relatively easy to install.
Fiberglass is not prone to cracking like plastic, and does not require confinement around the liner like preformed plastic liners do. By not requiring confinement, we mean that the liner does not have to be completely surrounded by compacted sand or soil to help support the liner. In the case of preformed plastic liners, confinement is important to prevent the plastic liner from bending out of shape and cracking. In the case of fiberglass ponds, it is not even necessary to dig a hole to put the pond in. If desired, a fiberglass pond liner can be placed directly on the ground, and then concealed with rocks, plants and other landscaping materials to create a pond that is elevated above the ground level.
One of the main advantages of fiberglass pond liners is the ease of installation. Unlike other liner systems, fiberglass is a littler harder to get wrong. Other than breaking the liner itself, the chance of creating a leaking pond is small. Fiberglass ponds are also quite resilient to winter conditions, as the material is able to flex slightly in the presence of ice.
Precast liners are available in a variety of interesting shapes and sizes, and because of their preformed shape, do not contain any folds or unsightly creases like a standard rubber or PVC pond liner would.
The main problem with fiberglass is its expense. Fiberglass ponds will cost much more in materials than a similarly sized pond using a flexible pond liner. On top of the cost of materials, since fiberglass ponds are rigid and heavy, the shipping costs can be many times more expensive than shipping a flexible liner.
Another potential problem is the shallow water depth in most fiberglass ponds. Often times, preformed ponds in general are simply too shallow to properly control the water temperature. It is for this reason that a fiberglass koi pond may not be the best idea since koi, and other typs of fish, require a relatively consistent water temperature. This can be overcome however by purchasing a pond that holds greater than 1000 galons, or 4500 liters of water, since the larger the volume of water in a pond, the slower the water will react to temperature changes. As well, try to get a preformed pond with as much as depth as possible since deeper water also helps regulate temperature. If you have no plans for putting fish in your pond, then water temperature fluctuations could be less important depending on your goals.
Box-welded liners are a good alternative to fiberglass in certain situations. Box-welding is the process of taking a flat liner and heat welding the seams to create some kind of 3D shape or 'box'. We carry a 36 mil polypropylene liner that box-welds quite nicely into various rectangular or circular shapes. We are able to box-weld the liner at our facility so that it arrives in the desired shape, ready to go. Like fiberglass, our polypropylene is safe for fish, plants and humans. In fact, it is approved for human drinking water applications, so any form of fish farming, aquaponics or gardening for human consumption are also approved. The main benefit the pre-box-welded liners have is their cost - they are much less expensive than fiberglass, and much less expensive to ship. The one possible disadvantage of box-welded liners over fiberglass is that they are flexible, which means they must be supported. For example, if building an above ground pond, tank or filter, some kind of frame must be built to support the liner. This can easily be built out of wood and then camouflaged with landscaping, rocks or other material. If putting the liner below ground, as long as the liner is properly backfilled with soil or other fill, the liner will have plenty of support in ground. To learn more, or see prices, please see the box-welded polypropylene liner in our store.
Fiberglass ponds are sometimes also called glassfibre ponds.