Influence of background pre-treatments on bond and water permeability of renders

Abstract

This work presents the results of an experimental study developed with the purpose of verifying the influence of background pre-treatments on bond and water absorption/permeability of renders. Five types of ceramic block masonry pre-treatment were tested: reference (with no pre-treatment), lime saturated solution, 1:3 usual spatterdash (cement and sand, by volume), spatterdash with PVA and spatterdash with SBR. Four days after the backgrounds were treated, premixed cement and lime mortar was applied on them. This render was tested at the age of 28 days for water absorption and permeability, according to the NIT 140 method proposed by CSTC, from Belgium, as well as for tensile bond strength, according to NBR 13528 (ABNT, 1995c). The results showed that the types of substrate treatment do not influence the render water absorption/permeability. On the other hand, they have a significant influence on bond strength. The substrates with spatterdash showed the best results, although their modification with polymers did not show improvement of bonding capacity. A good correlation was also observed between water absorption of pre-treated substrates and obtained bond strength, having as a result a relation of direct proportionality between the factors within the evaluated interval. It means that, under the trial conditions, the higher the substrate absorption, the higher the bond strength, which was obtained as a result of spatterdash and specially with no addition of polymers.