Fiberglass planters are popular because they're lightweight and durable. In order to make a tall fiberglass planter, you will need a mold on which to lay the fiberglass. This can be either an actual metal mold that you will have to purchase or a tall ceramic or clay planter that you want to replicate. You apply the fiberglass to the surface of the mold in layers of dry material that's individually saturated with catalyzed resin. Fiberglass is fairly easy to work with, and you can find it at a marine supply store or auto body supply store.
Cut four six-inch-long pieces of two-by-four using a table saw. Glue the pieces of two-by-four to the inside of the opened end of the mold, using a hot glue gun. The two-by-fours will act as legs for the mold to lift it off the ground.
Prepare the surface of the planter mold by applying three coats of mold wax with the foam applicator, and let it dry. Wipe the excess wax from the surface of the mold with a clean rag.
Cut the fiberglass mat to size using a razor knife so it completely covers the surface of the mold. Use the first layer of mat as a pattern for the next three layers, giving you a total of four layers.
Put on rubber gloves, and mix the resin with the catalyst in a small bucket using a stir stick. Wet the surface of the mold using a felt roller. Apply the first layer of mat to the mold and saturate it with resin. Flatten and remove any bubbles from underneath the mat using an air roller. Repeat this process for each layer of mat until all layers are applied. Let the fiberglass cure until it's hard and cool to the touch.
Sand the open-end edge of the planter until it's even with the mold, using 100 grit sandpaper. Lightly scuff the entire surface of the fiberglass to remove any burs or rough spots.
Insert the metal scraper between the mold and the fiberglass, and slowly work the fiberglass loose. Lightly tap the outside of the fiberglass with a rubber mallet to break the fiberglass free from the mold. Remove the mold from the fiberglass.