Resin is a durable form of plastic that you can easily mold into many shapes, either for decorative purposes, such as ornaments, or as part of a larger structure such as parts of self-assemble furniture. Because of the surface texture and low reactive quality of resin, it can be difficult to make paint bond to it, so a special technique is necessary.
Clean the resin using soap and warm water. Use a toothbrush to clean any nicks, creases or other difficult-to-wash areas where dirt and grime can accumulate. This will also remove any residue left over from the casting process that could interfere with your paints and will ensure the best possible adhesive surface for your paints to bond to.
Remove any residual flash from the surface of the resin by cutting it off using a craft knife. Flash is the result of the resin entering the joint between two halves of a mold during the casting process. While it is not always obvious when the resin has set, it can become a visible ridge when you paint your resin. Sand the resin down with the 800-grit sandpaper.
Examine the resin for air bubbles, gouges and other surface defects that will prevent you achieving a smooth surface when painting. Fill these holes in with epoxy putty and allow the putty to set. Sand the surface down with the 600-grit sandpaper to make the putty flush with the surface of the resin and thereby achieve a smooth finish.
Coat the resin with spray-on primer and allow it to dry. Lightly sand the resin with the 400-grit sandpaper and spray it with another coat of primer. Allow to dry and sand again with the 400-grit sandpaper to smooth out the surface. Spray a final coat of primer over the resin and allow it to dry.
Paint the resin using a paintbrush and acrylic paint. Apply the paint in several coats, allowing each coat to dry before moving on to the next. This helps to achieve a smoother and more professional finish. Once the paint is dry, spray the resin with a lacquer sealant to prevent the paint from chipping. Allow the sealant to dry fully.