In order to highlight fundamental design and construction errors, this paper briefly reviews our firm’s litigation-related evaluation of below-grade waterproofing failures at a university building (Figure 1) located in Northern California.
Consider the front portion with the low-sloped roof: this 70-foot-long area encloses a partially below-grade boiler room (Figure 2) with perimeter cast-in-place (CIP) concrete walls – commencing below-grade underneath the reddish precast masonry panels – that extend down to the concrete footings. Since construction, groundwater leakage had regularly occurred at the floor-to-wall transitions (Figure 3) and, during heavy rain events, this room additionally flooded over the top of the below-grade CIP walls (Figure 4).
Assisted by a preeminent local geotechnical firm, Engineered Soil Repairs, we excavated an OSHA-compliant test hole 13-feet down to the footings in order to evaluate waterproofing failures. Upon commencing this excavation process, we exposed a raggedy, ripped, and poorly terminated sheet waterproofing membrane (see Figure 5) applied atop a layer of bentonite clay: “Bentonite is granulated smectite clay that provides waterproofing capabilities by swelling to nearly 15 times its dry volume when it absorbs water. In hydrated state, under sufficient hydrostatic pressure bentonite becomes a water-repelling gel that will adhere to many different materials – concrete, stone, wood.”
Unfortunately, the lack of a counterflashed, tightly secured “termination bar” (Figure 6) across the top edge of the “shot-pinned” (using a powder-actuated nail gun ) membrane had facilitated rain- and irrigation-water flow behind the sheet waterproofing. Also note at Figure 6, Figure 7, and Figure 8 that we found below-grade holes (allegedly, per the defense, caused by “snails” ) in vertical caulk joints at the reddish precast masonry panels. A test probe inserted into the damaged caulking seen in Figure 8 extended into the boiler room at the area of water staining seen at Figure 4. Further, per the exemplar “blob” seen in Figure 9, note that large portions of the bentonite clay had washed out of the system due the the above-identified deficiencies. Finally, note at Figure 10 that the horizontal caulk joint separating these two wall systems was not bonded to the precast masonry panels – providing yet another route for water infiltration into the boiler room.
Figure 1 – Boiler room has perimeter CIP concrete walls – commencing below-grade underneath the reddish precast masonry panels – that extend down to the concrete footings. (Whitish pre-cast panels extend up from the red panels.)
Figure 2 – This CIP concrete wall encloses at 70-foot-long boiler room that serves the entire campus.
Figure 3 – Even during dry weather, groundwater infiltrated the boiler room at floor-to-wall transitions. The water stains at the lower CIP wall (at left) resulted from leakage occurring at the top of the concrete wall (see Figure 4).
Figure 4 – During rain events, water flooded down from the top of the CIP wall, which commences 20 inches below grade. (The precast masonry panels above are attached to the CIP walls with steel brackets.)
Figure 5 – Upon commencing the excavation process, a raggedy, poorly attached, and extensively torn sheet waterproofing membrane was exposed. (The missing section at the top of this photo had been extracted for sampling purposes.)
Figure 6 – The sheet waterproofing had been “shot-pinned” to the reddish precast masonry panels without a “termination bar” that would have served to prevent the membrane from tearing loose during later backfilling. (Also note at the top of this photo the holes in the vertical caulk joint separating two of these panels – also see Figure 7 and Figure 8. )
Figure 7 – (Same caulk joint seen in Figure 6.) Defense consultants argued that these below-grade holes were caused by “snails”. At the upper hole, light from inside the boiler room can be seen.
Figure 8 – Damaged caulking at transition between the reddish precast masonry panels (atop steel brackets) and underlying CIP wall. A probe inserted into this hole readily extended into the boiler room at the area of water staining seen at Figure 4.
Figure 9 – During excavation, we found this “blob” of bentonite clay directly below the ripped membrane seen at Figure 8.
Figure 10 – The horizontal caulk joint at the transition between the two wall systems did not provide a watertight bond.
Figure 11 – Multiple breaches in the waterproofing membrane were observed at all levels of the excavation.
Figure 12 – Contractor(s) severely damaged the sheet membrane during the backfilling process.
Figure 13 – Near the bottom of the excavated trench, breaches in the waterproofing still remained prevalent.
As evidenced by Figure 11 (near the top of the trench), Figure 12 (halfway down), and Figure 13 (very near the bottom), contractor(s) had extensively damaged the sheet waterproofing membrane during the backfill process. Groundwater infiltration through these numerous breaches certainly contributed to the ongoing leakage at the floor slab-to-wall transition seen in Figure 3.
It also is important to note the absence of any mechanism – e. g. , a prefabricated “drainage composite” such as Miradrain® (or its many competitors) and/or a backfilled layer of 3/4-inch “drain rock” – to: a) promote direct drainage down to the footing drains at the bottom of the trench, and b) thereby, to relieve hydrostatic “head pressure” against the extensively ripped sheet membrane caused by groundwater trapped in the poorly draining backfill.
Alleged “Snail” Damage at the Vertical Caulk Joints
As noted above, the defense argued that the holes seen at Figure 6, Figure 7, and Figure 8 in the vertical caulk joints at the reddish precast masonry panels resulted from post-construction consumption of the polyurethane by “snails”. We observed no such “snails” (or comparable polyurethane-eating gastropods) at the site. Instead, we opined that these joint failures resulted from improper installation of the caulking in a manner inconsistent with industry standard ASTM C1193 (Standard Guide for Use Joint Sealants) and the manufacturer’s installation instructions.
In particular, we noted that: a) the thickness of the applied caulking did not meet the manufacturer’s minimum requirements; and b) the absence of the required foam “backer rod” that would have provided structural support to this polyurethane caulking as these precast masonry panels thermally expanded/contracted on a daily basis. In short, we opined that these failures most likely had been caused by stretching of the undue unduly thin caulking.
During the ensuing litigation process, we highlighted key errors by the contractor and his subcontractors:
We opined during deposition that these egregious errors should have been obvious to any qualified contractor. The defense settled the case prior to trial.
