How to make a concrete coaster using the silicone mold

Materials:

  1. Portland cement: (the base material for concrete)
  2. Silica sand: (provides strength and texture)
  3. Water: (for mixing)
  4. Additives: Optional (helps with strength, curing time, or workability)
  5. Pigments or cement oxide: Optional (adds color to the concrete)
  6. Sealant: (acrylic sealer to protect and enhance the coaster)
  7. Contact adhesive glue: (for attaching the protective cork)
  8. Cork sheet: (protects surfaces from scratches)

Tools:

  1. Coaster silicone mold: (a flexible mold that makes demolding easy)
  2. Mixing container: (a plastic container or bowl for mixing)
  3. Measuring spoon and cup: (for precise mixing)
  4. Stirring sticks, spatula, or kitchen whisk: (for mixing the concrete)
  5. Protective gear: (gloves, dust mask, and safety glasses)
  6. Trowel: (to smooth the concrete surface)
  7. Sandpaper: (for sanding and polishing)
  8. Brush: (for applying the sealer)
  9. Electric vibrator: Optional (helps remove air bubbles, but tapping the mold works too)

Step-by-Step 

Step 1: Set Up Your Workspace
  • Cover your work surface with a protective sheet.
  • Wear gloves, a dust mask, and safety glasses to protect yourself.
  • Work in a well-ventilated area.
Step 2: Mix Your Concrete

In a mixing container, combine:

  • 1 part Portland cement
  • 1 part silica sand

Adding Additives (Optional)

  • If using additives (such as plasticizers, accelerators, or fiber reinforcements), follow the manufacturer’s instructions for the correct dosage.
  • Plasticizers improve workability, accelerators speed up curing, and fiber reinforcements add strength.

Adding Color (Optional)

  • Mix a small amount of pigment or cement oxide into the wet mixture.
  • Stir thoroughly to ensure even color distribution.

Adding Water

  • Gradually add water while stirring until the mixture reaches a pancake batter consistency.

Pro Tip: Always mix additives and pigments before adding water to prevent clumping and uneven texture.

Step 3: Pour into the Mold
  • Slowly pour the concrete mix into your silicone mold.
  • Tap the sides of the mold to remove air bubbles.
  • If using an electric vibrator, place it under the mold to help release trapped air.

Avoiding Air Bubbles: Not tapping enough can leave some holes in your finished piece.

Step 4: Set and Demold
  • Cover the mold with plastic wrap to retain moisture.
  • Let it set for 24 hours before demolding.
  • After 24 hours remove the coaster from the mold.

Patience is key! Demolding too early can cause cracks.

Step 5: Wet Sand for a Smooth Finish
  • Dip the coaster in water and start with coarse-grit sandpaper (240 or higher) to remove rough edges.
  • Switch to fine-grit sandpaper (400 or higher) for a polished finish.
  • Use water while sanding to minimize dust and achieve a smooth, refined surface.

Let It Cure Again

  • After sanding, let the concrete coaster cure for another 24-48 hours before sealing.
  • This ensures any excess moisture evaporates, preventing issues with the sealer.

Pro Tip: Wet sanding helps create a glass-like finish and enhances the concrete’s natural texture.

Step 6: Seal for Protection
  • Apply an acrylic sealer to protect against moisture, stains, and heat.
  • Use a brush, spray, or dip method to apply the sealer evenly.
  • You can repeat the process if you want to make sure the coaster is properly sealed. 
  • Let it cure for 24 hours before using.

Why Seal? Sealing makes the coaster waterproof and stain-resistant.

Step 7: Attach the Cork Base
  • Cut a cork sheet to fit the bottom of your coaster.
  • Apply contact adhesive glue and press the cork onto the back.
  • Let it set for a few hours before using the coaster. 

If you want to get this exact same bubble coaster master model to make your first mold and coaster, Download the 3D design file here and 3D print it. Click here to download it now!