Building a garden pond using fiberglass

Sunset, April, 1987

Building a garden pond using fiberglass

Building your own garden pond soundsintimidating and expensive, with troubling visions of concrete forms and underpinnings of steel. But it's quite a different story if you use fiberglass.

Whether you want to create a large, free-formpool like the one above or just a 2- by 3-foot accent pond, the process is surprisingly simple: you dig a hole, smooth its surface with sand, and, starting from the outer edges, lay resin-impregnated fiberglass mat on it. A finishing layer of resin with a coloring agent makes the fiberglass sturdy enough to take light foot traffic without cracking.

Unlike working with concrete, it's a processthat lets you set your own pace. You can cover a few square feet one day, stop, and resume a few days later. You mix only as much resin and hardener as you need at each stage. Should a crack develop later on, you can add another layer of resin and fiberglass over the crack.

Our pictures show how Bob Whitehead ofDanville, California, built the 20- by 50-foot koi pond shown on page 134. To use this process, first determine the pond's size and shape--it can be orderly and symmetrical or have a more natural-looking form. Since you'll be excavating, you can use the removed soil for a berm and perhaps a stream bed. (Mr. Whitehead ran a berm around two-thirds of his pond, and put a waterfall, boulders, and ground-cover plants along the water's edge.)

A bacteriological filter and swimmingpool pump clean the water; smaller ponds need only a submersible pump.

Cost and materials

The bigger the pond, the less each squarefoot costs. Ponds under 100 square feet will cost about $1.25 per square foot, medium-size ponds (up to 300 square feet) should run about $1 per square foot, and larger ponds will be about 75 cents per square foot. You save by buying the fiberglass mat and resin in bulk.

It's difficult to determine an exact square-footageof fiberglass mat for a pond, both because the hole you dig will have compound curves and because you must overlap each row of fiberglass by about 2 inches. For a rule of thumb, determine the square-footage of the pond's surface before it's dug and add 25 percent.

Shops specializing in fiberglass supplieswill have most of the materials (check in the yellow pages under Fiberglass). For any size pond, you'll need:

1 1/2-ounce fiberglass mat: long strands offiberglass pressed together. Cost: about $2.15 per running yard of 38-inch-wide material.

Type B polyester laminating resin: sold in1-gallon (about $19) or 5-gallon (about $70) containers. For the first coat, figure 1 gallon will cover about 20 square feet; for the second coat, a gallon should cover 100 square feet.

Liquid hardener: a catalyst added to setthe resin. You'll need 2 ounces (about $2) per gallon of resin.

Surface-curing agent: to be added to thefinal coat of resin, in addition to the hardener. You'll need 2 ounces (about $1.75) per gallon of resin.

Pigment: also added to the final coat;choose a dark color to make the pond bottom opaque. Use 4 ounces ($1 per ounce) per gallon.

Brushes: buy several 3- to 4-inch-wideinexpensive paintbrushes.

Acetone: for cleaning brushes.

Disposable plastic gloves.

Mixing tub and stirrer: fiberglass storemay have gallon-size paper tubs with graduated measurements on sides.

Polyethylene sheet (or other nonporousplastic surface): at least 4 by 4 feet; use over a hard, flat work surface when painting resin on the mat.

Old, expendable scissors.

Sand: enough to cover the pond bottomwith up to 1/2 inch of damp sand.

Start by digging

Ponds can slope gradually or drop offabruptly to the depth you choose. For fish to be comfortable, the pond should be at least 24 inches deep.

If you plan to add a waterfall, you'll needto install a submersible pump in a hole--8 to 10 inches deep for a small pump--at the pond's lowest point. Larger pumps will need buried electric and PVC water lines that pass through the fiberglass next to the pump (seal this point with several coats of fiberglass). A small system can be dropped in after completion.

Make sure that the perimeter of the pondis level. If needed, build up the edge with excavated soil and smooth out irregularities with damp sand. You can apply the sand to each area just before you put down the mat, or cover the whole pond with a thin layer of sand and smooth it as you go. For good bonding, be careful to keep the fiberglass free of sand.

The edge of your pond can trail off intothe surrounding soil with a gradual slope, or, for a more defined edge, you could build up a slight ridge using soil or the halved cardboard tubing shown on page 134. Small boulders or vertical wood posts could also accent the water's edge.

Laying down the fiberglass

Cut the roll of fiberglass mat into 19- by19-inch squares, then use them to cover larger areas. Use old scissors to cut the mat, because fiberglass quickly dulls them. For working around rocks or contoured areas, you'll need smaller pieces.

Prepare a work surface by covering apiece of plywood or heavy cardboard with the polyethylene sheeting. Wearing disposable gloves and following the manufacturer's instructions, mix up to a gallon of the resin and hardener. The "pot life' is only about 15 minutes, so work in small quantities. Between batches, clean the brush with acetone. If it's a hot day, the fiberglass will set faster; mix only 1/2 gallon at a time to work with.