Adhesion of Gypsum Plaster Coatings: Experimental Evaluation

Abstract

Nearly 95% of the Brazilian production of natural gypsum comes from the state of Pernambuco, from the Araripe Gypsum Center. Of the 95%, that is to say, of the 1.3 million ton/year production, 61% is allotted to the making of blocks and plates, 35% for coverings, 3% for ceramic moulding, and 1% for other uses. The Gypsum Center generates nearly 12,000 jobs directly and approximately 60,000 jobs indirectly, and has an annual invoicing of US$300M per annum. In civil construction, the use of gypsum increases continually, because plaster paste is seen by builders as a low cost, quality alternative material to be applied as coatings to internal walls. The reduced cost results in higher productivity on the part of the craftsperson due to the speed of application as well as providing a good final finish. Paint can be applied without needing to apply putty. Bases commonly used for these types of finishes are ceramic and concrete substrates. These materials are known for their excellent mechanical strength and low thermal conductivity. The superior surface quality on both sides of these materials makes them suitable for any thickness of plaster paste. This study evaluates experimentally the adhesion strength of coatings made with gypsum paste, considering different substrates and application heights. There are four types of blocks (ceramic and concrete, non-structural and structural blocks), two types of slice cutting (superficial and penetrating to the substrate) and three application heights (up to 0.6 m, between 0.6 and 1.2 m and above 1.2 m). The results indicated the strong influence by the base and depth of cut on the adhesion, but there was no influence on adherence attributed to the height of application.