Throughout human history a stone building has evoked feelings of strength and durability. Unfortunately many stone structures are anything but strong and durable. Stone is subject to natural weathering and corrosion from environmental pollution. Often these processes affect the stone so that over time visible changes take place. The changes can be merely unsightly or they can be symptoms of serious structural defects. Either case can lead to customer dissatisfaction, which in turn can end in costly remediation and possible litigation.
American Petrographic Services is a team of experienced geologists who can analyze dimension stone. We use the latest techniques of polarized light microscopy, scanning electron microscopy, x-ray diffraction, and chemical analysis. We also provide expert witness services in the litigation of construction defects.
We help you solve clients' problems with stone deterioration by giving you accurate analysis of the materials involved. Our analysis can:
- help with selection of proper materials for new construction
- provide needed facts to assess weathered and possibly damaged structures
- enable you to serve your clients to the best of your ability
- avoid litigation or assist in the process if litigation should begin
- give you and your clients peace of mind
The Basilica of Saint Mary in Minneapolis, Minnesota, was completed in 1914. The facade is made of the well-known Bethel White Granite from Vermont. In 2002, our laboratory was asked to assess the cause of some yellow coloration on the near white granite. We were also asked to determine what effect glass beads used to abrasion-clean stone work might have on the granite. We used polarized light microscopy to determine that the coloration was due to a slight alteration of the feldspar in the granite to clay minerals. This is a natural result of normal weathering. We also found that the glass beads had little effect on the granite and should be safe to use in the cleaning process.
Another client had a problem with coatings developing on bricks and dolomite blocks that were part of a landscape fountain. We used x-ray diffraction analysis in this case to characterize the fine-grained efflorescence. Crystalline solids give unique x-ray diffraction patterns that act like fingerprints and allow highly reliable identification of substances. Our analysis showed that the coatings were calcium carbonate and a mixture of sodium and potassium chlorides.
Salts like these have several deleterious affects on stone. Salts crystallize out of an aqueous solution into the pores of stone and brick. The pressure of this crystallization causes wedging that eventually cracks stone or brick.
Aqueous solutions of chlorides are also corrosive. These solutions attack the minerals in stone which, in turn, cause serious deterioration of the stone. They attack metal parts used as anchors and trim. Chlorides can enter the system from fertilizers, de-icer salts and water treatment chemicals. In this case, the source was lawn fertilizers.
Tombstones and archaeological artifacts such as the Kensington Runestone have also been examined by APS.