specs

Geotechnical Investigation South River Place, Gasser Drive, Napa 29 December 2010
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Slab-on-Grade Construction
Interior slabs utilized in conjunction with spread footings and exterior slabs-on-grade should be
constructed in accordance with the following recommendations:
a) All areas to receive slabs should be wetted to seal any desiccation or shrinkage cracks
prior to placing the underslab components. This work should be done under the
observation of the Soil Engineer.
b) Slabs should be underlain by a minimum of 4 inches of ¾” Caltrans Class II
Aggregate Base placed and compacted between the finished subgrade and the slabs to
serve as subbase support.
c) Slabs should be a minimum of 5 inches thick and be reinforced with a minimum of
No. 4 bars spaced 16 inches center to center, each way. The actual slab thickness and
reinforcement should be determined by the project structural engineer in accordance
with the structural requirements. The reinforcement shall be placed in the center of
the slab unless otherwise designated by the design engineer. Thickened edges should
also be constructed adjacent to landscape areas such that the slab rests on grade.
d) A vapor barrier membrane should be installed between the subgrade and the slab to
minimize moisture condensation under floor coverings and/or upward vapor
transmission. The vapor barrier membrane should be a minimum 10-mil extruded
polyolefin plastic that complies with ASTM E1745 Class A and have a permeance of
less than 0.01 perms per ASTM E96 or ASTM F1249. It is noted that polyethylene
films (visqueen) do not meet these specifications. The vapor barrier must be
adequately lapped and taped/sealed at penetrations and seams in accordance with
ASTM E1643 and the manufacturer’s specifications. The vapor retarder must be
placed continuously across the slab area, including closure strips. Therefore, the
membrane must extend beyond the closure strip contact to allow for adequate lapping
and sealing of the seam.
To prevent excessive moisture migration through the slab, and minimize the
occurrence of shrinkage cracking and slab curling, it is recommended that all slab-ongrade
concrete be placed with a maximum water to cement ratio of 0.5 and be
appropriately cured. In addition, the slab should not be subjected to rainfall or
cleaning water prior to placement of the floor coverings. Floor moisture emission
testing may also be required prior to placement of moisture sensitive floor coverings.
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KC ENGINEERING COMPANY Project No. VV3200 Page 21 of 123