Study on the effects of multiple primers on the pull-off strength of gypsum plaster and its mechanism

Although gypsum plaster has been well studied, there are few related researches on the effects of primers on the pull-off strength of gypsum plaster in the plastering systems. Therefore, the effects of no primer, vinyl acetate ethylene (VAE)-type primers, styrene-acrylic (SA)-type primers, and acetate-acrylic (AA)-type primers on the pull-off strength of gypsum plaster, were comparatively discussed. The results indicated that these primers all can chemically bond with the gypsum plaster and aerated concrete substrate, thus the adhesion of gypsum plaster on the substrate was promoted, and the failure type in the pull-off strength test changed from adhesive failure to cohesive failure. With the better permeability of primers and the lower degree of the pore blocking, the negative impacts on the gypsum dihydrate crystals were smaller, the mechanical interlocking force generated between the substrate and the gypsum plaster was larger, and the damage surface of cohesive failure is further away from the bonding transition area (plaster/primer/substrate). Therefore, the application of VAE-type primers and AA-type primers could increase the pull-off strength of gypsum plaster by 1.74-2.44 times and 1.70-1.90 times, respectively, while the application of SA-type primers would reduce the pull-off strength of gypsum plaster by at least 30%.