Question: Please discuss the method used to apply floor hardeners on a monolithic slab-on-grade floor.

Answer: You are undoubtedly referring to the use of mineral or metallic aggregate dry shakes applied to the surface before troweling. Such dry shakes usually contain about 1 part of portland cement to 2 parts of aggregate by dry weight. The aggregate may be a mineral such as crushed traprock, quartz or granite or it may be made up of treated or oxidized iron filings. If the dry shake contains iron aggregate it should not be applied to any concrete that contains calcium chloride. The procedure for using dry shakes is:

  • After bleed water and excess moisture have left the surface, power float or hand float the surface.
  • Distribute about 2/3 of the required amount of dry shake uniformly over the surface.
  • Power float or hand float the material into the surface.
  • Distribute the remaining 1/3 Of the dry shake uniformly over the surface.
  • Power float or hand float the material into the surface.

Trowel the surface as many times as necessary to produce a sufficiently hard wear-resistant surface.