An assessment was made of the performance of surface treatments for the conservation of masonry monuments, and, further, the risks of failure and damage were evaluated and methods for the prediction of the performance were developed. In the three European countries involved in the project over 60 case studies were carried out involving assessment of water repellents previously applied to historic brick monuments. Essential for the assessment of the performance of water repellents in the field and in the laboratory is the water repellent behaviour, checked on the brick/mortar system, and the evaluation of any damage observed, in relation with the presence of the treatment. This approach to the evaluation of the effects of treatments, using materials in combination, thus forming a system, proved to be very important: different behaviour of brick and mortar after treatment could be observed, as well as interactions and mutual influences. The effectiveness (water repellency) of a treatment can last for a long time (more than 30 years). To this conclusion the following should be added: there is no clear relation between the age of the treatment and its effectiveness; the effectiveness of the treatment within one building, even within one wall is quite variable; the mortar joint is, from the point of view of water penetration, the weakest part of the (treated) system. The main reason for poor performance of treatments involves in most cases, the lack of preliminary investigations, meant to outline the state of conservation of a building and to furnish the basis for: deciding on the necessity of a treatment; selecting the most suitable treatment product.
