Self-levelling gypsum paste for use as a subfloor layer

Abstract The subfloor is a layer of the floor system designed to smooth, leveland absorb deformations. Conventionally, subfloorsare made of a low-productivity dry cement-based mortar. The use of a self-levelling gypsum-based material allows faster curing, lower cost, and smoothness of the surface, as well asa lower thickness. This researchstudy aimed to develop self-levelling gypsum pastes (GSL), with only beta gypsum as a binder, as well as to evaluate the influence of the superplasticizer additive based on polycarboxylate (PCE). A dosage study was carried out on pastes containing a water-to-gypsum ratio of 0.35; 0.40; 0.45; 0.475; 0.50, and 0.55 along with the superplasticizer additive content adjusted for self-levelling spreading. The pastes were characterized in the fresh state as to the setting times, spreading and heat of hydration time. In the hardened state for resistance to compression, traction in flexion, surface hardness and SEM. GSL pastes were obtained with a water-to-plaster ratio of 0.45 and 0.475, containing 3.5 and 2.0% PCE, respectively. The PCE increased the setting times, modified the crystalline structure of the hemihydrate, and reduced the interlocking of the crystals with the consequent decrease in the mechanical properties.