Early ettringite crystallization in the presence of 2 chemically different polycarboxylate superplasticizers was studied by hydrating a commercial portland cement (CEM I 52.5N) for 10seconds. It was found that the presence of polycarboxylate superplasticizers leads to ettringite crystals which are longer, yet slimmer (higher aspect ratio), compared with the crystals obtained from neat cement paste. This finding suggests that the polycarboxylate (PCE) polymers predominantly adsorb on the lateral faces of the hexagonal-prismatic crystals of ettringite. For the methacrylate-based PCE, this effect increases with increasing superplasticizer dosage, whereas for the IPEG-PCE, the effect achieved at a very low dosage (0.05%) is not altered when dosage increases. The behaviors of both PCE polymers can be explained by their different adsorption behavior, whereby the IPEG-PCE reached the saturated adsorbed amount at much lower dosage than the MPEG-PCE. Microgravity only has a minor effect on the growth of ettringite. There, generally smaller crystals are observed.