• Concrete bases should be carefully measured and constructed.Jupiterimages/Photos.com/Getty Images
  
  When creating a garage or patio (or larger structures for commercial buildings), workers must pour the concrete slabs on site, since they are too large and too heavy for moving and positioning. Pouring on site allows workers to prepare the ground properly and make sure the slab is level. This also requires several important steps. If the slab is not poured correctly and leveled immediately, it can develop structural problems over time.
  
  

Measuring and Marking

• Proper concrete pouring begins with accurate measurements. If the first measurement for the slab is off, workers cannot level the slab once it is poured. Measurement typically begins with planting stakes and using string and plumb lines to measure the exact distance from corner to corner of the slab area, along with diagonal measurements. Workers mark the outline with chalk when they have the precise measurements.
  
  

Ground Preparation

• Once the ground is properly marked off, workers can begin digging into the soil itself. If the slab is poured in colder climates, workers will dig deep to create a firm base that extends beneath the frost line. At least several inches is a common depth. The workers then line the space with a moisture barrier to separate the soil from the concrete, and create a gravel base to pour onto.
  
  

Mixing Options

• With the area measured, dug and supported for pouring, workers need to decide how they will mix and pour the concrete. There are two general types of mixing strategies. If the concrete slabs are large and require a lot of mix, then workers will typically hire a cement truck to come out to the site and pour directly onto the base, or use a concrete pump to draw the mixture over the base. If the project is small, then workers will mix and pour the concrete using a wheelbarrow and shovel.
  
  

Leveling

• Once the concrete is poured, workers must spread it using shovels and other tools, moving it out evenly across the base. Workers then use a screed pole or board, a level plan that they rest on the wooden borders of the base and pull back and forth across the slab. This flattens and levels the concrete, showing where more concrete needs to be added to create a fully level surface.