Polystyrene beads are a familiar item if you've ever owned a bean bag chair, but you probably didn't know you can create lightweight concrete by adding them to the mix. As a very light but strong building component EPS concrete, or expanded polystyrene concrete has highly insulating properties and can create a stone-like surface for creative projects. Garden statues, curved projects, panels of energy-efficient homes or unusual items such as concrete counter tops can be created using EPS concrete. Adding the polystyrene beads mainly requires knowing the ratio of the mix.
Use a ratio of one to six for the mix of cement to polystyrene. Use equal parts Portland cement, sand and water. For example if you have 1 cup of Portland cement, mix it with 6 cups of polystyrene beads plus 1 cup water and 1 cup sand. This recipe is obviously very small but gives the correct ratio.
Place the water in a large bucket such as an empty 5-gallon bucket, the concrete mixer or the wheelbarrow. The wheelbarrow can be cumbersome for mixing but if the batch is relatively small it should work. The bucket works for very small projects.
Add the Portland cement and sand to the water and mix well to create a soup. This should be a very wet consistency, not usual for cement because the polystyrene will soak up a large amount of the water. Use the shovel to mix by hand or turn the cement mixer on if you have one.
Place 1 part of the polystyrene beads in, allowing them to begin to be absorbed in the mix. Add 1 more portion, then another, until all of them are absorbed. Stop mixing as soon as the beads are mixed in. If the mix seems dry add a small amount of water so it comes to a less stiff consistency. The mix should be somewhat thick and not soupy, and what is called low-slump, meaning it holds its shape but is not too wet or too dry.