Effectiveness of silicon based water repellent agents at different application conditions. Part II: commercial water repellents

An investigation had been carried out on the application modalities of silicon based water repellents on building materials. From previous studies with silicon model compounds it was known that for volatile compounds, the polymeristion reaction is mainly influenced by the type of substrate and reaction conditions are not as critical. For non-volatile compounds, reactivity increases with conditioning temperature, while the substrate plays a lower role. The present paper focuses on the effectiveness of commercial silicon based water repellents when applied at temperatures between O and 55 degrees C. Due to the complex nature of commercial products and the presence of crosslinking agents, a quantitative evaluation of the polymerisation mixture could not be carried out as in the case of the model compounds. The effectiveness of the treatment is based on water absorption measurements carried out during and after artificial ageing. For brick it is concluded that there is a tendency towards lower water repellent characteristics for temperatures between 10 and 40 degrees C. with a minimum at 30 degrees C. For limestone, the lowest effectiveness is obtained at 35 degrees C. for water repellents having a dry weight between 6.5 and 9 per cent. The results confirm the conclusions from the research carried out with the model compounds which showed that applications at a low temperature (0-5 degrees C) will not necessarily result in a poorly performing treatment.