Makeup – Rebar Foundation

When the plumber has completed the foundation plumbing ‘ground’, the home is ready for foundation make-up. The material for this work consists of 6 mil. Black polyethylene, several rolls of plastic tape and black plastic roofing cement or ‘mastic’ – not oil!

The foundation make-up crew digs out the foundation beams according to the foundation plan. Grades the sand to provide the desired thickness of slab and installs the vapor barrier consisting of 6 mil polyethylene. He seals all slab penetrations with tape and plastic cement.

If the plumber has not dug a drainage trench, the make-up crew will dig a trench from the slab to the street to provide drainage. This protects the make-up contractor’s work from major damage from rain and standing water.

When all beams have been dug, the grade is correct and the poly has been completely installed, the make-up contractor builds ‘cages’ of rebar which are wired to the inside of rebar ‘stirrups’ per the structural engineer’s specifications. Once the rebar cages are built, they are lowered into the beams and supported by bricks so that concrere will flow completely around the rebar cages. The rebar cages are connected using tie wires. Special corner bars should be made and installed per the engineering to form a continuous rebar reinforcement. Then
either welded wire mesh is installed or a rebar ‘mat’ is constructed using rebar rods in a checkerborard pattern. The rebars are wired together and supported by rebar ‘chairs’ to hold them in the center of the concrete. Dowells may be used to reinforce inside corners. Some engineers will have special requirements such as void boxes, etc.

Items that you should check:

  • Address is posted
  • Check Slab Thickness
    • Check with your engineer to confirm your desired slab thickness. Generally engineers design slabs to be from 3-1/2″ to 4-1/2″ thick (not including foundation
      beams). Run a string line across the form from one side to the other. Measure down from the string with a tape measure.
    • Note that when you place your concrete, the weight of the concrete will tend to compact your foundation sand – up to 1/2″. For this reason, your grade on your
      foundation ‘pads’ must be extremely ‘tight’. A difference of 1/2″ on a 3000 Square Foot slab will add over 4-1/2 cubic yards of concrete. That amounts to
      over $500.00!
  • Check Beams – Location, Depth, and Width
    • Confirm that the beam locations, depth, and width correspond to the plans. Confirm the size of the beams using your foundation engineering. Note that
      beams should be ‘centered’ under walls. Many make-up crews do not center their beams under walls and this could be a structural issue.
  • Stub-Outs are Sealed
    • Plumbing and other slab penetrations need to be sealed with mastic and / or duct tape.
  • Poly Splices are Taped
    • All seams in the Poly vapor barrier should be taped. There should be no holes in the poly.
  • Poly Follows Beam Contours
    • Poly must follow the beam contours and rest on the bottom of the beam.
  • Poly Covers the Bottom of Exterior Beams
    • Poly must cover the bottom of the beams at exterior walls.
  • Check Raised or Dropped Areas
    • At raised or dropped areas, sand should be dropped. Allow for slope of 12 inches out for each inch of drop. i.e.: a 4″ drop in slab elevation must be sloped
      4′ from the drop.
  • Check Pipes Crossing Beams
    • Poly should run under pipes crossing beams. There should be 4″ of concrete under all pipes crossing beams.
  • Check Wing walls and Column Footings
    • Maintain beam depth in wing walls and column footings.
  • Check Dropped Areas
    • Confirm that sand graded at raised or dropped areas will allow for the proper depth of concrete under ‘float’ forms. Float lumber dimensions are usually 3-1/2″
      to 5-1/2″.
  • No Lumps or Holes in Sand Under Poly
    • Slab ‘pads’ should be even and contain no lumps or foreign material.
  • Wrap Slab the Same Day
    • Do not allow a ‘made-up’ slab to sit overnight without being wrapped with poly.
    • Damage can occur from weather, vandalism, playing children, etc.
  • Confirm Plumbing was Not Damaged
    • Check with the make-up contractor as to whether his crew may have damaged any underground piping when digging the beams.
    • If there is ANY damage, DO NOT POUR the slab until it has been corrected.
  • Trench Dug for Beam Drainage.
    • Trench should be lower than the foundation beams and run to the street to prevent the beams from holding water.
  • Rebar cages are built per the engineering.
    • Cages are built outside of the form and are dropped in and connected using tie wire or wire ties.
  • Rebar stirrups are manufactured according to dimensions from the engineer.
    • Rebar stirrups are custom-made according to your requirements. Be sure that you order these to allow room for concrete on all sides of the rebar cage.
  • Rebar cages are supported with bricks or as specified by the engineer to keep the steel off of the bottom of the beam.
  • Rebars overlap as specified in the engineering and are wired properly.
    • See the engineering for more on overlap specifications.
  • Rebars used are the correct size and quality and are not touching the sides of the beams.
  • Corner bars are the size and strength specified on the engineering and have been installed as specified.
  • Re-entrant corner bars at inside corners are in place per the engineering.
  • Fireplace areas are reinforced as required on the engineering.
  • Rebar mat has been constructed at the spacing designated by the engineering.
  • Rebar chairs have been installed to support the rebar mat at the spacing
    designated by the engineering.
  • Sight or run a string line across the top of the form to ensure that the steel reinforcement is below the level of the top of the form.
  • All conduits, downdraft vents, raceways, etc have been installed in the slab as needed.
  • Jobsite is clean