SGH investigated the condition of the exterior masonry bearing walls, which vary from 6 ft at the bottom to 3 ft at the top. We observed cracks, previous repairs, a deteriorated collar joint between the sandstone cladding and the granite masonry, and numerous coating layers.
In our laboratory, SGH analyzed coating and repair mortar samples. We identified the coatings prevented the masonry from drying and accelerated freeze-thaw deterioration. We also concluded the repair mortar failed due to deterioration and expansion of the material’s iron constituents.
To help us determine why the lighthouse was cracking, we modeled the lighthouse structure and performed a thermal stress analysis to examine temperature gradients through the thickness of the walls. SGH concluded seasonal temperature differences between the sandstone cladding and the granite core likely initiated cracking. Long-term water penetration and freeze-thaw damage further deteriorated the collar joint.
We provided the Montauk Historical Society with a report detailing our findings and three repair concepts for rehabilitating the lighthouse.