Editor’s Note: This is the second part of a two-part series exploring stone flooring failure and inspection issues. The first part appeared in the March/April issue.
When discussing sample collection and laboratory analysis, petrographic analysis is the description and systematic classification of rocks, aided by the microscopic examination of thin sections. In other words, a thin slice of stone, setting mortar or concrete is taken and examined under a microscope. A geologist can then identify minerals and other components.
Petrographic analysis can be useful to the stone investigator by providing clues as to what caused deterioration of the stone surface. It can detect foreign materials in the stone and concrete substrate. It is also valuable in identifying the components of the mix of the setting m ortar or slab.
When collecting samples for petrographic analysis, make sure you check with the lab for instructions on what they require. Also include as much information as possible with the sample to give the lab a better idea of the problem.
While I am not a professional photographer, I have learned a few tricks. Avoid using a flash, especially on polished stone. I like using a digital camera so I can preview my shots and avoid having to come back and retake them. You can burn all the photos to a disc and include it in your report.Take photos from different angles. This is helpful in viewing certain types of problems, especially detail. If you’re taking close-ups, place a ruler or scale in the photo for size reference. Make sure to record the frame number so you know where you took the photo. I will sometimes place numbers in the shot so I don’t confuse the location, etc. Make sure to record the date you took the photos.
One reason for a floor installation failure may be that it was not designed in accordance with industry standards or codes. The inspector must be familiar with the proper design standards and codes. In cases where the placement of expansion joints is not specified, the inspector may need to hire a structural engineer or architect to render an opinion. This is especially true if there is a structural issue.
Laboratory vs. Field Investigation
Many experts use laboratory testing to reach misleading conclusions. While laboratory testing is helpful, it should not be relied on without comparing the results to field data. The following case study is an example of how laboratory testing can be misleading.
Project: A black granite wall experienced streaking, which ran down the face of the wall. Most of the streaking occurred at the joints where the panels of the stone met. The joints contained a black silicone caulk.
Investigation: The wall’s owners hired a laboratory that took numerous wipes of the area for analysis. The surface where the streaks occurred were wiped with some clean cotton cloths in an attempt to collect samples of the streaking material.