Depron foam is sturdy styrofoam that is a popular choice for building architectural models as well as model aeroplanes. The foam comes in thin sheets and is manufactured in both open and closed cell versions. The closed cell version is great for model construction because it can be painted and will be water resistant if treated with a topcoat.
Build your model. Perform all of the cutting and assembly of your model before you begin painting. Cuts and handling after you paint may cause the paint to chip or scratch.
Rub the model with rubbing alcohol. Rubbing alcohol cleans the surface of the Depron and removes chemical film from the foam sheet. The paint will adhere to the surface of the foam sheets and will be less susceptible to peeling and scratches.
Place your model on a dust sheet or newspaper. Use trim tape to tape off any areas that you don't want painted. Trim tape that is safe for Depron can be purchased at most hobby shops.
Spray the model with a light dusting of white foam safe paint. Foam safe paint can be purchased at hobby shops online or at most craft stores. Humbrol and Krylon both make paints that are safe for foam. Apply a light coat of paint to act as a primer for any colours that you plan to add to your model. Hold the spray about 12 inches from the model and spray the paint allowing it to lightly dust the model. Allow the paint to dry completely.
Spray paint a base coat of paint on the model using foam safe enamel paints. Choose your paint carefully. Many paints will cause the Depron to disintegrate. Make sure that the label indicates that the product is safe for use on foam. Spray the model using multiple thin coats of paint instead of one thick coat. Multiple thin coats will create a smoother finish with fewer drip marks. Use a steady back and forth motion to apply the paint. Allow the paint to dry.
Remove drip marks. Use a sheet of fine grit sandpaper to lightly rub out drip marks. Wipe away the sanding dust with a damp rag. Touch up the paint as necessary with spray paint.
Add details to your model using a small artist's brush. Use a foam safe enamel paint that is sold in small tins.
Decals resist sticking to Depron foam. Using rubbing alcohol to prepare the surface prior to adhering decals will help them to stick. Paint will also create a surface that decals can grab onto.