To mix polystyrene and cement successfully, you must blend cement, sand, water, and an adhesion additive before gradually folding in crushed polystyrene beads. Because polystyrene is incredibly light and contains roughly 98% air, it tends to float or separate from heavy wet cement. Using a bonding agent prevents this separation and produces lightweight, insulative “EPScrete”.
Standard Mixing Ratios
The exact ratio depends on how lightweight or structurally strong you need the final block to be
- Standard Lightweight Blocks: 1 part cement, 3 parts medium sand, and 4 parts crushed polystyrene (by volume).
- Insulation/Cooling Layers (Non-structural): 1 part cement, 1 part sand, and 6 parts polystyrene beads.
Standard Mixing Ratios
The exact ratio depends on how lightweight or structurally strong you need the final block to be.
- Standard Lightweight Blocks: 1 part cement, 3 parts medium sand, and 4 parts crushed polystyrene (by volume).
- Insulation/Cooling Layers (Non-structural): 1 part cement, 1 part sand, and 6 parts polystyrene beads.
Step-by-Step Mixing Process
1. Prep the Polystyrene
- Grind the foam: Use raw expanded polystyrene (EPS) beads, or grind up recycled packing foam blocks.
- Achieve the right size: Shred the foam into pea-sized particles using a dedicated grinder or home blender.
- Safety gear: Wear a mask and gloves, as static-charged micro-particles easily fly into the air and cause irritation.
2. Prepare the Liquid Adhesion Mix
- The Problem: Plain water will not easily coat polystyrene due to its surface properties.
- The Solution: Dilute standard white PVA carpentry glue into your mixing water. Alternatively, use a commercial concrete liquid plasticizer or a small splash of liquid dish soap. This additive acts as a wetting agent, reducing material porosity and making the beads stick seamlessly to the cement mortar.
3. Blend the Dry Ingredients
- Combine base materials: Mix your dry Portland cement and medium-grained sand thoroughly in a wheelbarrow or bucket.
- Mix until uniform: Ensure the color is completely homogeneous before introducing any liquid to prevent clumping.
4. Create the Base Slurry
- Pour the liquid: Slowly add your water and PVA glue mixture to the dry cement and sand.
- Stir thoroughly: Mix until it reaches a smooth, soupy consistency.
5. Integrate the Polystyrene
- Add in stages: Introduce the crushed polystyrene foam gradually, rather than dumping it all in at once.
- Fold gently: Mix continuously by hand or with a low-speed mixer to avoid tearing the delicate foam beads.
- Check consistency: Stop mixing once you achieve a crumbly dough consistency. When you squeeze a handful, it should form a firm ball that holds its shape without dripping excess water.
Crucial Working Tips
- Avoid over-vibrating: Do not use mechanical concrete vibrators once the mix is poured into your molds. Shaking the forms causes the ultra-lightweight foam to separate and float right to the top. Instead, gently tap the outer sides of the mold to settle air pockets.
- Extended curing: EPScrete holds moisture longer than traditional concrete. Leave your items in their molds for at least 48 hours. Once demolded, let them cure in a well-ventilated, shaded area for 7 days, lightly moistening them daily to prevent micro-cracks.