This project is part of a $30 million project completed in 2002 in Western Montana. The architect specified HMK S39 Silane Impregnator, but the sealer was only used near each joint as a way to protect the stone from the urethane caulk joints, and any smearing or residue. No impregnator was applied to the face of the stone, and no regular maintenance was completed, even though a maintenance plan was part of the architects specifications.
Fast forward to 2016, and with a combination of neglect and a faulty wall flashing, the elements have severely effected the look of the Indian Sandstone. See images below:
You can clearly see where the clean stone is adjacent to the caulk joints that has been protected from the elements since 2002. The HMK Silane Impregnator worked where it was placed. It is very unfortunate that the same product was not applied to the face of the stone. So in a word YES…exterior stone DOES need to be protected with a quality impregnating sealer.
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