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- Concrete repair: Repair methods and troubleshooting basics
- Read more about foundation repair on FoundationRepairNetwork.com
- Houston Foundation Repair: Answers to common questions about foundation problems in Houston
What is Slabjacking?An overview of how slabjacking fixes sunken concrete
Pictorial Overview of Slab Jacking
A grout mixture is pumped under the slab with our specialized equipment. Once any void is filled, the grout becomes pressurized, hydraulically raising the slab to the desired height.
The holes are patched using a concrete mixture.
Photos Courtesy of Concrete Slab Jacking, Inc. in Maryland USA
If your concrete is sinking, there is a very good possibility that the concrete slab was installed on poorly compacted fill dirt. Sub-surface erosion and shrinking soils are also possibilities.
If you are fortunate enough to have a slabjacker in your area, you should not have to replace the concrete. These individuals can float a slab back to its original position by pumping a mixture of sand, cement, fly ash, and other additives beneath your slab.
They simply drill strategically placed holes into the slab. Using a portable pump and flexible hoses, they fill these holes with the special mixture. Lifting a slab using this method can often be accomplished in a few hours.
Often the cost to perform this sort of concrete leveling is less than half that of replacing a new slab.
There are numerous benefits to slabjacking.
- It can be done in virtually any weather. The material injected beneath the slab provides a strong base.
- There is little or no disruption to landscaping.
- Nothing needs to be moved off the slab, as the pump can lift the weight of the slab and anything you have placed on it.
Why concrete sinks in the first place
Fill dirt is almost always placed along side of house and garage foundations after the foundation work is completed. This fills in voids created during the foundation construction process. Rarely does a builder take the time to compact this dirt.
Soils consist of solid particles and the spaces (voids) between these particles. However, void spaces in soil can cause big problems for buildings and concrete slabs. Concentrated loads, such as buildings or slabs can literally squeeze air and water from soils.
When this happens, the soil sinks and the buildings or slabs follow closely behind.
Avoiding the problem from the start
The problem could have been avoided. Instead of installing fill dirt, a builder should install granular fill such as sand or a sand and gravel mix. These materials can be compacted quite easily with a hand held vibratory compactor.
This material should also be used to fill trenches that cross sidewalks and driveways.
Proper compaction will remove air voids, which if not removed, will later settle and cause the concrete to crack and sink.
Advantages of Slabjacking
Slabjacking has many benefits:
- The grout used to raise the slab provides a stable base, thus strengthening the slab.
- Low cost: The cost to raise the concrete slab to its original position is approximately one third compared to replacement.
- Since slabs are not being removed, there is very little mess or inconvenience.
- No loss of use: Concrete leveling allows the client to use the slab immediately. If the slab is replaced the concrete has to cure for a minimum of 28 days.
- There is no waste involved, compared to slab replacement, where the removed material will end up in the landfill results are better environmentally.
- There is no noisy concrete breaking, with its associated dust and debris.
- Slabjacking can be performed in almost any weather conditions.
- Surrounding grass is not dug up, so there is no reseeding and waiting for new grass to grow.
- Because the old slabs are still there, the color of the concrete remains constant.
Problems/ Solutions When Repairing Concrete Foundations
Problem: Grout doesn't pump into hole, or squirts back out.
Solution: Blow out the hole with air or drill further into the sub-base.
Problem: New cracks form or old ones are enlarged.
Solution: Usually a problem with technique: pumping too much grout into one hole, using grout that is too stiff, or pumping holes in the wrong sequence. Rule of thumb: don't lift a slab more tha an inch while pumping at one hole.
Problem: Slab lifts in wrong place.
Solution: The grout may be too thin. Leave the hole for a while, and come back with a thicker grout.
Problem: Slab binds against concrete and won't rise.
Solution: Grout may be flowing beneath an adjoining slab, use a thicker grout. You can also relieve binding by chipping concrete the edge of the slab, sawing a relief slot all the way through the slab, make sure joints and cracks are clean before starting to pump grout.
Problem: Grout leaks through cracks or joints at the side of the slab.
Solution: Let it set up, then resume normal pumping. Leaks at the slab edge can be stopped by using a thicker grout.