Rock Dust Vs. Topsoil When Concrete Lifting: Concrete lifting, as the name implies, deals with portions of previously installed and cured flatwork concrete that has settled below its original elevation. That original concrete purpose may be a driveway, sidewalk, patio, steps and porch for a residential home. Often interior floors of a building or residence are installed as a concrete slab on grade. In all cases prior to installation a sub base is prepared with the purpose to stabilize and support that flat concrete during its expected lifetime. That usefulness is intended to span many decades. A property owner wants it to remain level, without deterioration, or spalling to provide safe and smooth access to the property. Concrete Leveling offers excellent info on this.
Throughout Utah many types of soils dictate how well any flat concrete will wear due to years of traffic and natural exposure. Seasonal freezing and thawing, excess moisture from irrigation systems or rainfall may undermine even the best prepared sub grade. Generally, a soil type has sufficient granular materials to give long term stability; however, some soils are expansive meaning they expand and contract in response to moisture and freezing temperatures. That instability is bad news for concrete on grade. Those surfaces on expansive soils will respond and move due to underlying changes of their grade. In addition, gutter and downspouts come unattached or become clogged with leaves etc and deposit water near the foundation and concrete slabs. This causes reverse drainage and settlement near those concrete features, compounding any damage problems caused by excess moisture.
Slab lifting is an excellent solution to problems aging concrete surfaces experience. This method has been in existence for 50 years or longer. Originally the term mud jacking was used to describe the use of topsoil as the key filler ingredient. Mixed with a portion of Portland cement it provides a pressurized lifting process that would bring a concrete slab back to its original elevation. Although topsoil is cheap and available it has a natural tendency for further deterioration since the average organic material in Utah topsoil is 5%. These soils in their natural state will break down and provide nutrients for plants. Settlement, resulting from this inherent composting process, will normally occur. Many slab lifting contractors recognizing this problem have sought more suitable filler materials.
Rock Dust, a product of ground up limestone and available for safety requirements in the local coal mining industry, is an excellent replacement for topsoil in the concrete slab lifting process. This material is mixed with Portland cement and pumped through 1 ½ drilled holes under the concrete slab. After all voids are filled the dispersed pressurized materials exert and upward pressure and a controlled lift will bring that slab back to its original elevation.
One of the long term benefits of this inorganic material are stable warranty issues. Those slab lifting contractors using Rock Dust experience few call backs. There is no filler material breakdown and therefore no resulting settlement due to their process. Those in the industry using topsoil experience up to 20% warranty callbacks. In new construction supervised by an architect or a licensed engineer, require 6-8″ of topsoil be stripped from the construction site, especially for areas a where concrete surfaces will be installed.