Hardiflex boards can be installed over wood or steel framing.  All construction shall comply with local building codes, including the use of vapor barriers where required.  Unheated spaces above ceilings should be properly ventilated.

Framing members and other surfaces must be straight, true, of uniform dimensions and properly aligned.  Petronne steel framing is recommended.  


  1. Hardiflex boards should be installed on the ceilings first.  Application at right angles to the framing is preferable.
  2. Unless specified on fire or sound rated assemblies, horizontal wall application is recommended to give added strength and reduce the number of joints.
  3. Starting in the upper corner of the wall, work across and down.  Ends and edges of sheets should be touching but not forced tightly together.  
  4. Holding Hardiflex board firmly against the framing, begin fastening in the center of the sheet and moved outward toward ends and edges.  
  5. Set fasteners heads slightly indented from the surface without breaking the face paper or damaging the gypsum core.
  6. Installed sheet in a brick pattern with the ends staggered and supported by framing members.  Joints shall not fall on the same studs as those directly on the opposite side of the wall.
  7. Cut openings out of full sheets or lay out joints to fall on the studs nearest the center of the doors and windows.  Where possible, position full sheets to extend completely above and below openings and avoid piecing.   

Control Joints

Control joints, as specified and detailed by the architect, shall be installed in the following situations:

  • In ceilings exceeding 2500 sq. ft. in area and where the framing or furring changes direction.  The distance between control joints shall not be greater than 50 ft. in either direction.
  • In partition, wall and wall furring runs exceeding 30 ft. in length.  Distances between control joints should not be greater than 30 ft..  Wall  or partition height door frames may be utilized as control joints.
  • Opposite of where a control joint occurs in the exterior base wall construction.
  • To coincide whenever possible with construction joints of the building. 

When partitions are erected to span the full height of the slabs between floors as required for fire or STC rated assemblies, a perimeter relief joint shall be used at the top to accommodate normal structural slab or beam movement without loading partition.

Joint, Corner and Surface Preparation

These areas should be finished in accordance with ASTM S 840, the GA - 216 and the joint compound manufacturer's instructions.

  1. No treatment of joints shall be done until the interior temperature has been maintained at a minimum of 50F for at least 48 hours prior to application of compounds and until all materials have completely dried.  Adequate continuous ventilation must also be provided.
  2. Fill and level joints with joint compound.
  3. Embed tape into the wet compound and allow to dry.  For inside corners, crease the tape and work it into joint.
  4. Apply a second coat of compound across the joint, feather to approximately 4 inches on each side.
  5. Apply a third coat of compound and feather to approximately 6 inches.
  6. Allow each coat of compound to dry before proceeding.
  7. Attach corner bead to outside corners and apply three coats of compound.  Feather out each coat as described in steps 4 - 6.
  8. Spot cover all fastener heads with three coats of joint compound applied in different directions.
  9. Lightly sand the last coat of all treated areas, taking care no to rough the surrounding gypsum board paper.  Smoothing can also be accomplished with a damp sponge.    


  • Gypsum board must not be used in areas that are continuously or repeated exposed to excessive moisture or steam such as saunas, gang shower rooms or swimming pool enclosures.
  • Gypsum board should not be exposed to sustained temperatures exceeding 125F.
  • The weight of ceiling insulation shall not exceed 2 pounds per square foot.
  • Sheets should not come in direct contact with concrete masonry or other surfaces that have a high moisture content.
  • Not recommended for use with radiant heat ceilings.

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