Concrete Settlement 101

Have you noticed your driveway sinking? Is your sidewalk uneven? These may be signs of concrete settlement.

Concrete floor slab settlement is often the result of changes in moisture content or density of the supporting soils. For example, soils beneath a concrete slab can dry and shrink over time due to extended drought-like conditions, leaking HVAC systems, etc. Loosely-compacted fill soils can also consolidate beneath the weight of the slab or fill layers above. A different condition, plumbing lines under the slab can leak, in turn, piping soil out and away from under the concrete slab. Each of these conditions creates a void under the concrete slab. If the concrete slab is not strong enough to span the void, the slab will crack, break, and settle into the void. 

Options for repair that are less desirable, alternative methods that don't work:

Concrete slab replacement- Very expensive, very disruptive, and does not address the problem (slab likely to settle again)

Mudjacking- Messy, high-pressure grout spews out of other holes and cracks in the slab, does not address the problem (slab likely to settle again)

Re-leveling grout on top of slab- Adds additional weight, potentially making the problem worse, additional grout may dislodge if it doesn't bond well to existing slab, does not address the problem (slab likely to settle again)

Helical Slab Piers- Heavy equipment needed on site, relies on the empirical formula to calculate capacity, difficult to install in areas of limited access.

Author: Foundation Support Works 2014 "Slab Pier System" Brochure

Here are a few causes of concrete settlement:

Drying and Shrinking of Soil Under the Slab

Settlement occurs if the soil underneath a concrete floor slab has dried and start to shrink.

Poorly Compacted Fill Soils

When homes or buildings are being constructed, often layers of soil are spread out to lift the grade to a desired level. After the structure is built, the footings may extend below the fill soils, but the slab could remain on top.

 Washout of Soil from Plumbing Leaks

It is common during the construction of a home or building to install plumbing lines below concrete slabs. Soil can wash away if those plumbing lines beneath a slab start to leak. The displaced soil can create a void beneath the slab, causing the slab to crack and settle.

Redeemers Group offers solutions to your home’s slab settlement issues. Give us a call today to take care of your slab settlement needs.