Fiberglassing a pond is not difficult so much as it is time-consuming. The job---whatever the size of the pond---is best done with the help of a few friends or family members to assist in moving and setting fibreglass fabric pieces to complete the project. The overall project, depending on the size of the pond, should only take a couple of days and should only be done when the forecast calls for sunny skies.
Drain the pond of water if full using a pump. Leave some water in the base to soak into the soil and let the soil pack down. Let the floor of the pond dry before proceeding.
Set flexible pond liner into the empty pond. Trim away excess with a pair of scissors. Leave enough excess to lay around the pond's rim while fiberglassing. Place several bricks around the pond's rim on top of the liner excess to hold it in place.
Position fibreglass matting over the liner. Cut any excess away with scissors. The fibreglass matting should completely cover the liner and pond. Repeat the process, adding at least three more layers of fibreglass matting on top of the liner. Remove all fibreglass matting layers but the first one and set them aside.
Put on eye protection, gloves and a respirator. Mix catalysts and resin together in a bucket, following the manufacturer's specific directions. Stir the catalysts-and-resin mixture with a paint stirrer for a couple of minutes, or as long as recommended by the manufacturer.
Coat the first fibreglass matting layer with the mixture using a paintbrush or roller. While the mixture is still wet, put the next layer of fibreglass matting down on top of the first layer. Coat the second layer with the mixture and repeat the process for each additional fibreglass matting layer. Allow the mixture to cure and dry for at least one day or as long as directed by the manufacturer.
Sand the fibreglass with an electric sander with heavy-grit sandpaper to even the surface and remove any splinters. Then, smooth over the surface with fine-grit sandpaper. Vacuum out the dust with a shop vacuum or brush it out with a broom.
Mix catalyst and gel coat in a bucket following the manufacturer's directions. Apply the mixture to the sanded surface with a roller or paintbrush. Let it dry for 24 hours and apply a second coat. Allow the second coat to dry for the same length of time before adding water to the fiberglassed pond.
You may paint the fibreglass pond after the second application of catalyst and gel coat is completely dry.