Lifting settled concrete with a point load

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Raising settled concrete porches and patios –

One of the most challenging concrete raising jobs we are asked to do is raise a slab with a “point load”

A point load is generally a section of concrete that has a structure on it. Often a beam or pillar supporting an overhead roof or a block wall built on a slab without a foundation, but we’ve seen things like large brick BBQ’s too. Point loads are also created when support structures are attached to the concrete UNDER the slab. Lifting either of these can create problems.

Generally Speaking when concrete settles with a point load on TOP, a crack will develop somewhere near the point load. If it settles with a point load under the slab, a crack may or may not develop. Let’s talk about three different scenarios;

The first will be a very common porch with overhead roof with a pillar for support attached to the porch. As long as there are no sub grade “Sonotubes” we can raise these just fine. Injections will be made right at the point load to reduce the possibility of cracking the porch.

The second type, a block wall built on a converted car-port either for enclosed garage space or converted to living space.  When the weight of a block wall and roof are loaded on the edge of a slab settling can occur, especially if a plan wasn’t made for the elimination of water run off and snow melt. When this happens it is nearly possible to generate lift (Slabjack) only at the edge and not at the crack. If the settling is minor 1/2″ or so, the elimination of water and monitoring the settling may be sufficient. If the settling is more severe, then foundation piering may be necessary. (Look for our foundation piering section in our blog index)

The third type, the under slab supports are also a problem. In theory settling should not occur with a separate support poured to load bearing soil and this is generally true, however the ones that settled weren’t. The challenge of course is that in addition to raising the porch or the patio with these under slab supports we have to drag the support up too and this is where problems arise. Most of the time lifts are attempted without isolating the supporting structure from the slab, the slab will break near the connection between the two. The only way to raise a slab with under slab support is to cut the support away from the slab. This can be done two ways, the easiest is to use a saw and cut around the support. After the slab is raised new concrete will need to be poured to fill that section. The second method is much more time-consuming. An excavation is made so the concrete support is exposed which is then cut off. The hole refilled and the Slabjacking process used. For patios this method is financially impractical but for large porches it may make sense.

Point loaded concrete presents challenges to concrete leveling contractors. Chooses wisely or you may hire someone without sufficient experience or knowledge to successfully raise your concrete or to direct you to where you should go to properly deal with the issue. Call the concrete raising and leveling professionals today,


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