Exposed aggregate is one of the most versatile decorative finishes for concrete flatwork. Exposed aggregate surfaces are also non-skid and resistant to wear and weathering, making them ideal for sidewalks, driveways, patios, and pool decks. One of the oldest and most widely used techniques for horizontal exposed aggregate finishes is seeding. The seeding method requires no special formwork and the only tool required, other than basic finishing tools, is a stiff brush.
Use seeding aggregate particles that are uniform in size. Rounded aggregate usually takes less time to seed than crushed aggregate. Concrete for the base slab should meet requirements outlined by the ASTM C 94 Specifications for Ready Mixed Concrete. Use a three-quarter-inch-maximum-size coarse aggregate in the base concrete to simplify embedment of the seeding aggregate. Immediately after screeding and bull floating the base slab, sprinkle the aggregate by hand or shovel onto the slab surface until the surface is completely covered with a layer of stone. Embed the aggregate by tamping and floating the surface. To expose the aggregate, wait until a foot placed on the slab surface does not leave an indentation, then lightly brush a small area of the slab with a medium to stiff nylon-bristle broom to remove excess mortar. If the aggregate dislodges easily, delay exposing the aggregate. Cure following standard moist-curing procedures.