Drawbacks manifested during salt decay tests of using ethyl silicate as a consolidant in bricks made with added volcanic ash

In this study, handmade clay bricks made with and without added volcanic ash from La Palma (Canary Islands, Spain) and fired at 800, 950 and 1100 °C were consolidated with ethyl silicate with 75 w/w%, the concentration recommended by the manufacturer for direct application onto building materials suffering from decay. The efficacy of the consolidant was assessed by analysing the pore systems, hydric behaviour, colour changes and dynamic elastic properties of consolidated and unconsolidated bricks. Their susceptibility to decay was assessed using salt crystallisation tests. The ethyl silicate successfully reduced the porosity of the treated samples, slowed water drop absorption and improved their compactness and elastic moduli to some extent. In the salt crystallization tests, however, higher levels of decay were observed in treated bricks than in untreated ones. This means that ethyl silicate at the tested concentration should not be regarded as an effective consolidant for bricks of this kind in environments where soluble salts are present. As for the colour of the bricks, although only slight differences were observed at 800 °C, these intensified at higher firing temperatures, a factor that should also be taken into consideration.