- Concrete slabs home
- Before you begin: Avoid these 7 common mistakes
- Make sure the subgrade is compact
- Use a low water-cement ratio: How to calculate
- Subgrades and subbases for concrete slabs: Tips for ensuring good support
- Concrete Slab Finishing Tips
- How to Prevent Cracks
- Important guidelines for preventing cracks in concrete slabs
- Be active in deciding where control joints will be placed
- Proper Curing of Concrete Slabs
- Properly curing concrete slabs: Why and how
- Allow enough time to water cure
- Related Information:
- Concrete fasteners
- Concrete forms
- The three types of concrete foundations
- Aggregates in ready-mix concrete
- Vapor barriers for concrete slabs
- Post-tensioned concrete slabs
- Concrete slabjacking
- Concrete testing
Build a High Quality Slab on Grade
Why build a high quality slab on grade is best answered with, "what happens when you don't!"
If the concrete is out of level (greater than ¼" in 10') it causes expensive shimming or cutting of framing. If corrections are not made during framing lid lines (where the wall meets the ceiling) may be noticeably out of level.
If the water cement ratio is above .50 the concrete can be overly permeable causing adhesives for vinyl flooring to loosen, mold or mildew to form under vinyl, vinyl to yellow, and grout in tile to become wet. Excessive cracking can cause further problems with flooring materials and water permeation through the slab. Learn more about using a low water to cement ratio.
If air entrainment is not used in the mix in cold weather climates, water inside the concrete can expand when freezing temperatures hit and fracture the concrete.
If control joints are not used with the proper spacing and placement unsightly cracks can develop, telegraphing through vinyl or breaking tile grout. Learn more about control joint placement.
If wire mesh is used in the slab but blocks to support the mesh are not used the mesh can end up on the ground-not in the concrete, thus cracks that develop may widen causing problems with flooring or water permeability. Consider fibers in the concrete mix instead.
If the subgrade is not compacted and the ground becomes saturated after a good rain, the plumbing trenches under the house may collapse or the utility trenches connecting to the street may collapse under the driveway or other concrete flatwork-leaving no support for the concrete.
If the concrete is not properly cured the concrete may develop cracks that would not otherwise have occurred. Proper curing delays the drying shrinkage until the concrete is strong enough to resist shrinkage cracking. Concrete which is moist cured for 7 days is about 50% stronger than concrete exposed to dry air for the same period.