The performance of the phosphate treatment as a consolidant for marble and limestone has proved to be exceptionally good. After being damaged by thermal treatment, the dynamic modulus of marble and limestone is returned to its original value by a single treatment with the phosphate consolidant. Direct comparison shows that it is superior to commercial silicate consolidants. Moreover, the HAP treatment does not substantially reduce the moisture transport through the stone, and does not confer hydrophobicity. Therefore, we expect this procedure to become widely used for treatment of weathered carbonate stones.
For quartzitic stones, silicate consolidants are superior, but they render the stone hydrophobic, which prevents moisture transport and hinders additional treatments, such as application of mortars or renders. We discovered that the hydrophobicity of the consolidated stone could be strongly reduced by a simple rinsing with an aqueous solution containing only about 16% ethanol. This allows the stone to be made hydrophilic within a week or two of consolidation, without excessive release of VOCs. We expect this procedure to be of great interest to conservators.
This research was made possible through MT-2210-12-NC-08 from the National Center for Preservation Technology and Training (NCPTT).