Different ways of making backgrounds

What are the main ways to create a background and the pro's and con's for them?

I know a couple of the different methods used are:

• clay cat litter
• foam covered with aquarium grade silicone and coco husk
• foam covered with PVA (with paint mixed in for colour) and coco husk

I've already foamed my background and bogwood into place but can't decide what is the best method for sealing the foam and making a natural looking background