Sculptures are pieces of art that take a lot of time and effort in not only the design, but also in the preparation of the material. Artists need to decide what their subject is going to be and how they are going to sculpt it. Some materials can be placed outside and withstand the natural elements, while other materials will collapse after being touched by water. To make a sculpture waterproof, there are a few easy ways, and then there are more difficult methods using sturdier material.
Pick which type of material you would like to use for your sculpture. Research the materials you will be able to work with to do your best work.
Research your area and see if there is anywhere you could do bronze resin or other resin-type sculptures. These are not only waterproof but weatherproof.
Make a sculpture out of whatever material you chose to work with. Even if you are able to find somewhere to work with resins, you still need to design the sculpture to make the mould for the resin.
Bake or glaze sculptures made of clay to solidify the material and make it waterproof. Baking will solidify the clay to make it very hard and waterproof, and glazing is done to finer clay such as ceramics to make them waterproof. Plasters and papier mache are not waterproof materials, but can be made waterproof with thick, clear varnishes. Suspend these pieces so that they do not touch any surfaces and coat the entire sculpture with the varnish. Do not lower the sculpture until the varnish is dry.
Make a mould from your original sculpture to use for either cement, bronze or metal resins that are all waterproof materials. Take it to a local studio where they work with these metals and oversee the final steps to your finished statue. You will get a lighter product using resins than a statue made of pure bronze, cement or copper.