Rebar hangers are 2-inch square thin steel base plates with a wire welded perpendicular in the center and barbs protruding the opposite side from the wire. These barbs are pressed into the initial 1.5 inches of foam – before the additional layers of foam are applied. Refer to Polyurethane Foam Application. Rebar hangers are part of the Airform package. If more are needed, contact Monolithic.
Attach one rebar hanger at the top center of the dome. To secure the center top hanger, spray a thin layer of foam over the hanger. If rebar hangers are not covered with enough foam, they will not be secure enough to hold the rebar. Sometimes we place two hangers at the top in case one breaks.
The top center hanger is now used as a marking guide. To mark placement of other hangers, tie a non-stretching string or wire to the top center hanger. Attach a marker/chalk to opposite end of the string. Begin marking for hangers at the dome’s base as noted below and work upward.
Rebar Hanger Placement Specifications
Rebar is spaced and placed per engineering. The rebar steel in the dome can be divided into four categories. The hanger location is different for each category of steel.
Footing to Building Connection Steel: This is the steel rebar in the footing that has been bent down. The footing uprights do not require rebar hangers, however, horizontals that cross the uprights do. Rebar hangers should be placed in rows about 12-inches apart vertically beginning at the base and staggered every 3 to 4 feet apart horizontally.
Opening Perimeters: The concrete should be reinforced around any door, window, or other opening. Precisely place these hangers. Rebar is often used to outline the openings. The extra steel is tied to the face of the other steel.
From the base of the dome: 3/8" bars are placed on a 12-inch horizontal grid, 12-inches apart vertically, starting at the floor and continuing to the top of the dome approximately three feet apart horizontally, depending on engineering.
After the rebar hangers are placed, secure the hangers by completing the foam spraying job with 1/2 to 3/4 inch of foam at a perpendicular angle to prevent excess foam buildup on the hangers. When foaming is complete, begin tying the rebar.
Note: These are general instructions and measurements for rebar hanger placement. Always refer to specified engineering for exact placement.