Sealing Exposed Aggregate Concrete
When selecting a sealer for exposed-aggregate concrete, the main qualities you are looking for are:
When applying the sealer to fresh concrete, make sure all cement paste residue from the exposure process has been thoroughly removed to avoid sealing the milky-looking white paste on the surface. On existing exposed-aggregate concrete, thoroughly clean the surface from oil, grease, dirt, and stains before applying a sealer. (See Cleaning Concrete.) Use a short-nap roller for the best application results.
Whichever brand of concrete sealer you use, be sure to follow the specific instructions for the product, both for surface preparation and application, and make sure the sealer is recommended for use on exposed-aggregate concrete. This link provides a list of concrete sealer manufacturers.