Case Studies: The Klingler Group

The Leaky Roof and Pitted Clay Tiles: A Closer Look

The homeowners of a single-family home in Scottsdale experienced a roof leak and hired a roofing contractor to evaluate the cause. The contractor determined that the clay tile roof had sustained hail damage and would need to be replaced. The homeowner's insurance carrier contacted The Klingler Group for a second inspection.

In collaboration with the roofing contractor, we went onsite to investigate.

Roof Construction

The roof consisted of two separate gables configured in an "L" shape design, with four primary roof slopes facing every direction. The home is situated with the front elevation facing north. At the back or south elevation, a low-slope patio roof made of hot asphalt is covered with a mineral-cap-sheet surfaced with a white elastomeric coating.

Initial Assessment: Hail Damage

We found the pitting condition of the clay tiles on all four slopes to be consistent with the roofing contractor's assessment of hail damage.

However, we also observed the following conditions:

  • Some replacement tiles at various locations did not show the same level of damage.
  • The roof flashings, consisting of sheet-metal tops with lead skirts, showed only small signs of denting on the soft metal lead; the sheet metal portions were unblemished.
  • No damage was found to the back patio roof.

Hail generally shatters or breaks tile in a splayed pattern originating from the impact location, and the windward roof slopes usually sustain more predominant damage. We suspected that if hail was the culprit, it was a high-density hail with an increased thermal velocity.

Closer Look: Lime Pops

We asked the roofing contractor for two tile specimens, one replacement and one original, so we could conduct a more thorough analysis. Upon returning to our facilities, we examined the clay tile specimens with an electronic digital microscope, which provides real-time imaging through the eyepiece as well as the ability to send the image to a computer, where it can be enlarged for more detailed inspection. The image revealed that what appeared to be simply hail damage onsite was actually a condition resulting from "lime pops", which are caused by impurities in the process of making clay tiles.

Lime pops are the result of white or gray deposits made up of quicklime particles from limestone which have been heated at high temperatures during the process of making the clay tiles. These small particles react when exposed to higher levels of humidity and expand over time, creating pinhead-sized lime pops.

We found quicklime deposits in both the damaged and the new replacement tile specimens. Magnified images provide evidence of the particle expansion and popping.

The underside of the original clay tile exhibits a limited number of lime pops. Since this side of the tile faces the roof deck and is not exposed to the elements, the surface clay material blister has not de-bonded. The surface of the original tile represents that these "blisters" have been knocked loose, exposing the quicklime deposit; in every location the deposit is visible.

The replacement tile images show the same type particles within the clay with no lime pops. Whether this new tile would react the same way as the original tile is unknown, however most likely if the deposits are close to the surface, they would react to humidity in the same fashion.


Based on our initial field assessment, we felt that the roofing contractor's conclusion was reasonable. It was our further belief that the pitting was from an intense hailstorm, and that hail was not the only issue. By conducting a more detailed examination, we reached the conclusion that the clay tiles were contaminated with quicklime particles which expanded and created lime pops. We concluded that the damages to the tile, with a volume of popping greater than what is commonly observed, were the result of "dirty clay". Although a product deficiency, the damage may have been exacerbated over time through various storm occurrences.

With the integrity of the clay roofing product compromised and the life expectancy reduced; it was our opinion that the clay roof should be replaced.

Marginal or unique hail damage is difficult to identify, and the performance implications are not always fully understood. Limited field evaluation, which cannot consider all potential factors, may lead to an inaccurate or incomplete analysis. By taking a closer look, The Klingler Group was able to make a proper assessment and recommend suitable repairs.

  • Water path indicated by arrows
  • Void at deck which allows water to enter soffit cavity
  • Water intrusion at closet behind sheetrock
  • Inferred image at closet lid above metal framing: dark blue indicates water intrusion location
see also:

The Case of the Roof Leak that Wasn't
Roof Collapse
Interstitial Condensation
Damage Caused by Drainage Issues
"Punch List" Inspection Prevents Disaster
The Leaky Roof and Pitted Clay Tiles: A Closer Look