A Comparative Study of Alkoxysilanes and Acrylics in Sequence and in Mixture

A limestone column at Mission San Jose, San Antonio, Texas (USA) exhibited the friability, microcracking and flaking that is typical of saltcontaminated stone. Mixtures of acrylic resins and alkyl alkoxysilanes are frequently used to treat these problems. The deterioration was localized, however, and it was not advisable to introduce the potentially adverse effects of the acrylic in the mixture to relatively sound stone. The adhesion of subsequent infills would also be adversely affected by the water-repellency of the silane. Sequential applications of acrylic and silane would be more practical, flexible, and potentially more effective. The interaction of these materials, and their effectiveness when used in sequential order, has been little studied. An experimental programme was designed to quantify differences in the physico-mechanical properties of models that were caused by the application of acrylic and silane in sequence, rather than in mixture. Test results indicated that the method of application did not cause great differences in most properties of the treated models, but that mixtures were somewhat more effective. Based upon these results, and the treatment requirements of the column, the limestone was treated with a sequential application of an acrylic resin and an alkyl alkoxysilane.