Case of the Month: Crumbly Concrete

Jan 2, 2018 by

The homeowner’s kitchen floor seemed to have soft spots. The vinyl flooring was pulled back to reveal “crumbly” concrete. The concrete in the hallway under that same kind of vinyl flooring seemed okay and the concrete garage slab was okay. The client needed to know the cause of the “crumbly” concrete in the kitchen.

GEI was assigned to inspect the home to identify and determine the predominant cause and approximate age of the damage observed.

Front of residence

 

Our expert inspected the residence in the presence of the homeowner. The property was a single-family, single story, wood-framed, constructed circa 1989, slab on grade home with a concrete driveway and sparse (desert) landscaping.

The kitchen and dining room measured 11 feet by 22 feet. They were located on the east side of the house next to the carpeted living room and adjacent to the garage, which was at a slightly lower elevation.

The vinyl flooring was removed from the kitchen at the time of the investigation. The finish surface exposed remnants of a mastic or glue over some leveling compound. This was over some Portland cement topping, which was on top of the concrete slab.

Slab under kitchen floor

The slab had a minor crack across the middle of it, which is where a crack would normally be expected to occur. The surface of the concrete exposed a “pump mix” matrix of small aggregate, sand, and Portland cement paste in most areas, which would be expected for a pumped-in concrete product, but pockets of the concrete slab surface showed a lack of Portland cement, which allowed the finish surface to appear sandy in texture.

Slab under kitchen floor slab showing crack

The sand in these pockets was easily scraped off, giving a shallow crater appearance.

Slab showing rough surface

 

A 10 foot long straight edge was placed on the slab. The slab was straight, indicating that the sub grade had not settled.

Slab showing sledgehammer strike

The expert used a small 5-pound sledgehammer to strike the center of the concrete slab near the existing crack. This test did not break or crack the slab. This indicated that the concrete slab was generally strong, and of a proper thickness.

Based on the foregoing, it was the expert’s opinion that the predominant cause of the flooring damage was that when the concrete slab was originally poured, there was an inconsistent mix of Portland cement. Some areas received the proper proportion of Portland cement in the concrete mix, such as the garage floor and the hallway. Other areas lacked the proper proportion of Portland cement, which caused the sandy, rough surface that was crumbing under the kitchen floor. The observed damage was caused by an inconsistent mix of materials in the original concrete mix.

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