Settled concrete slab foundation or floor? Concrete Jack’s experienced foam jacking and slab jacking crews are slab foundation repair experts and can raise your settled floor for a fraction of the price and almost none of the disruption associated with slab piers or replacement. Unlike overlays such as self-leveling floor treatments, foam jacking and slab jacking address the cause of floor settlement to help ensure the longest lifetime repair possible. Typical, foam jacking doesn’t require removal of all floor coverings. Concrete Jack has experienced foam jacking and slab jacking crews who have repaired thousands of slab foundations, from single family homes to grocery stores and warehouses.
Causes of Slab Foundation Problems
The most common cause of slab foundation settlement problems is improper backfill placement. The general sequence of floating slab floor construction is to install the exterior walls first, then install any needed plumbing, electrical, HVAC or other utility lines under the slab. After the utilities are run, sand, stone or dirt are spread out to level the surface. If the fill material isn’t compacted or has potential to consolidate over time, it settles over time. This settlement causes voids (air spaces) to develop under the slab foundation. Very few slabs are designed to act long term as bridges over these voids, so the slab will eventually crack and start to settle. After your home is built, the rule of thumb is that it takes about 10 years for the soil placed during construction to settle, which removes support from the floor. Floors generally settle slower than the soil because of the friction against adjacent walls, floors and area of adequate support. Sometimes plumbing, particularly sewer lines, can develop bellies and misaligned joints which can cause further problems. We recommend having an independent plumber check your sanitary sewer lines under your floor as part of a floor lifting project. Sometimes, if there has been extensive settlement of a floor which has ductile iron or other rigid plumbing under it, we will use grout injection first to help protect the plumbing lines prior to foam jacking. Drainage problems can also be the cause of slab foundation problems. A downspout which dumps out right next to your foundation can cause the rainwater to soften the underlying soil, reducing its ability to bear weight. Over time, this allows the foundation to settle (think of the difference of stepping in deep mud instead of onto dry soil). Drainage problems can also cause soil to actually wash away or erode from under your slab foundation. This is quite rare.
Signs of Slab Foundation Problems
There are a few typical signs of slab floor settlement:
Floors are supposed to be installed flat. If you feel like you’re going downhill while walking through your home, your floor’s likely settling. If you have to shim under your furniture to make it sit level, the floor has likely settled. However, some slabs are installed with slope intentionally, such as patios and garage floors, so when they are repurposed to finished space, there will typically be a leaning feeling.
When different slabs next to each other settle different amounts, trip hazards can develop at the joints between the slabs. Trip hazards inside of homes are relatively rare in that usually slab floors are monolithic (one big piece) and reinforced. Old homes without reinforced slabs can sometimes develop large cracks with differential settlement (one side is lower than the other).
Cracks in floors
Sometimes cracks indicate settlement, but cracks are a guarantee in almost all concrete, so just because concrete has cracked doesn’t mean that it has settled or has a structural problem. Cracks form before settlement, so they can be a good leading indicator of problems below your concrete slab foundation. Cracks in floor slabs are often hidden by floor coverings, but will reflect through tile.
Gaps under baseboards
Gaps under your baseboards are one of the surest signs of slab floor settlement. Many homes are designed so that the majority of the structure’s weight rests on the exterior foundation walls, so as the slab starts to settle the floor pulls down from the walls, leaving a gap. Over time, the framed structure of the house will settle down, which can cause gaps under baseboards upstairs in multi-story homes.
Uncharacteristic crown moulding
Crown moulding is frequently installed to cover up gaps at the top of walls which settle with the floor slab. If you’re looking at a house that’s priced at half the comps, it feels like you’re walking down hill coming into it, and there’s crown moulding in every room, the walls have likely pulled down from the ceiling as the floor settled.
As walls settle or are pulled down by settling floors, door frames can twist, causing doors to “rack” or twist, which can bind the door and keep it from opening and closing properly.
Methods for Slab Foundation Repair
Foam jacking is the preferred method for lifting settled slab floors. Foam jacking is a quiet, fast and clean process and most times floor coverings and furnishings can remain in place. We have lifted 800 square foot floors that had dropped more than three inches using just two dime-size holes in less than three hours. In cases where there are exceptionally large voids under floors (more than 16 inches deep), Concrete Jack can install cellular concrete to fill the large voids prior to lifting with high density polyurethane. Occasionally, problems deep in the soil need to be addressed in addition to the slab settlement. In these cases, push or helical piers may be installed, particularly in areas with very heavy loading. Chemical grouting may also be used to treat underlying soils to solidify them into rigid bearing columns, as an alternative to installing piers.
Cost of Slab Foundation Repairs
Slab foundation repair using slab jacking or foam jacking typically costs less than a third the cost of replacement. Foam jacking minimizes the cost of flooring repairs because the injection holes are small (dime-size) and relatively infrequent. For example, for tiled floors, we can drill holes at the four-way intersections of tiles in the grout lines and then patch the holes with stained concrete close to the color of the grout or tile. For carpeted floors, we can cut back small squares of carpet, or you can roll it back for the work. Generally, furniture can stay in place during work. Any baseboards or other finishes which have been adjusted to disguise or accommodate the settlement need to be removed prior to lifting. The amount of polyurethane foam required to fill voids below the floor is one of the primary drivers of cost. For homes that don’t have large voids, foam jacking is usually no more than about $7 per square foot. However, if the area is very small, travel becomes a larger component of the cost, and therefore the square foot price may be higher. Also, if there are large voids, which need to be filled as part of the process, extensive interior finishes, etc, the cost may be higher. Slab piers, which some companies install to stabilize floors, generally cost around $30 per square foot, are very messy, and don’t do a good job of actually lifting the settled floor, and still require filling under the floor with foam or grout afterwards. To see more detailed comparisons between the costs and benefits of various slab foundation repairs, see our page about the cost of slab foundation repair. Concrete Jack offers payment options for most foundation repair projects.