This is the aggregate composition that I will be using. I came up with it by following the Fuller curve used for asphalt aggregates. But unlike other formulations on that ungodly long EG thread I wanted an aggregate that was cheap and obtainable from local stores. All components are either from Home Depot, from garden supply stores or from Harbor Freight.

Attachment 270320

From left to right the components are:

  • 27% - Quartz Rock (10mm)
  • 20% - Salmon Bay Rock (6mm)
  • 14% - Olimpia #2 Sand (#10, 2mm, only the largest particles)
  • 8% - Coarse Sand (#20, 0.8mm)
  • 9% - Medium Sand (#25, 0.7mm)
  • 6% - Fine Sand (#45, 0.35mm)
  • 16% - Glass Beads (#80, <0.2mm)


The percentages are fractions by volume.

To this you add 20% by volume of epoxy resin.

The numbers in brackets are the sizes of the particles in mm and/or the grit size for sands.

Now, I measured the compaction ratio of this mixture and it turned out to be 20%. That means if you want to fill a mold with volume V you need aggregate with total volume of 1.2*V. When mixed and compacted its volume will be V. Also note that epoxy plays no role in volume calculations since it is there to simply fill the gaps left in the aggregate after it is fully compacted.

The glass beads are from Harbor Freight and they are actually made for sand blasting, but should work well here too.
Everything else is bought either from Home Depot (fine and medium sand) or from garden supply stores (everything else). Everything needs to be clean though, so I washed and dried the quartz and salmon bay rocks.

Here are the bags with the various components of the aggregate.

Attachment 270322

Well, that's it, the next step is casting!