THE USE OF MAGNETIC-RESONANCE-IMAGING TECHNIQUES IN ASSESSING THE UPTAKE OF SURFACE TREATMENTS AND WATER-MOVEMENT THROUGH STONE FACES

This paper addresses some practical questions regarding the influence of hydrophobic treatments on the movement of water in sandstone. The b road line gradient echo magnetic resonance imaging technique has been used for monitoring the depth of penetration of alkyl alkoxysilane tre atment into untreated sandstone and subsequently to visualise the move ment and spatial distribution profile of water in the untreated and si lane treated sandstone matrix. The experimental results show that the effect of hyrdrophobic treatment depends on whether the stone is in sh ort-term or prolonged contact with water. For short term exposure, the presence of a silane treatment prevents the movement of water into an d out of the sandstone matrix. However, after continuous long-term con tact with water the hydrophobic treatment is unable to prevent the ing ress and internal redistribution of water. The ability of water to inf iltrate treated regions of sandstone has significant practical implica tion for stone structures where deterioration may be due to outward mo vement of water from the interior to the surface of the stone matrix.