Ettringite is responsible for both the initial set of Portland cement and for premature concrete deterioration. A new method of ettringite crystal growth by combining calcium hydroxide and aluminum sulfate solutions was devised to reliably produce crystals that could be seen with a light microscope (45×–320×). The nucleation, growth, morphology, and stability of ettringite in the presence of over 300 chemicals and admixtures, many of which are present in the concrete environment, was then investigated. The plasticizers sorbitol, citrate, and tartrate were found to inhibit ettringite nucleation and growth, as did certain lignosulfonate air-entraining admixtures. The Type B set retarder borax inhibited ettringite formation at <44 ppm. The consequences and implications of this are discussed.