·         Keys

o       A non-wicking pad on which the slab can crawl

o       Tougher moisture and vapor impermeable membrane than commonly applied

o       Deeper sub-base of crushed gravel

o       All the tamping

o       Clean substrates on application 

·         More commonly, substrate application involves one or more of these substandard materials and methods in this home designer's opinion –

o       Thinner subbase of large, crushed rock, thereby reducing the drainage plane

o       Smoother sand in lieu of the crusher run or equivalent, thereby permitting constant wicking and holding of moisture sub-slab and offering a much softer base for puncturing the membrane

o       Dirty or unwashed substrate components less prone to bonding

o       A 6-millimeter or so polyethylene membrane

§         In lieu of the high-density polyethylene for spaces not air-managed, thereby laying down a moisture impermeable membrane much more vulnerable to puncture during both setup and placement

§         In lieu of the InsulTarp or equivalent (if there is one) for spaces managed, thereby laying down a moisture impermeable membrane much more vulnerable to puncture during both setup and placement

o       Closed-cell polystyrene panels in lieu of InsulTarp, thereby offering crawly critters lifetime lodging that deteriorate the thermal barrier, presents no reflectivity, and can't come close to the InsulTarp's PERM rating for moisture impermeability 

·         A house foundation slab-on-grade 

o       Shall be placed preferably by pumping

§         Over rebar on only CRSI (a/k/a Concrete Reinforcing Steel Institute) Class 1 or Class 2 rebar chair supports

§         Over not less than 1-2 linear inches of stone dust (a/k/a crusher run, dense grade aggregate, DGA) to 5/8 linear inch diameter

o       For interior slab-on-ground, exterior patios and paths or

§         Over not less than 2 linear inches of stone dust (a/k/a crusher run, dense grade aggregate, DGA) to 5/8 linear inch diameter

§         Over membrane of cross-laminated high-density polyethylene sheeting (a/k/a high-density polyethylene, or HDPE), if interior space in unheated

§         Or over membrane of InsulTarp, if interior space is heated

o       For driveways

§         Over not less than 4 linear inches of stone dust (a/k/a crusher run, dense grade aggregate, DGA) to 5/8 linear inch diameter

§         Over membrane of cross-laminated high-density polyethylene sheeting (a/k/a high-density polyethylene, or HDPE)

§         Lapped at seams, penetrations, terminations and then sealed to not Less than manufacturer's specifications

o       Where the membrane is

§         Either carried across footings, pile caps, grade beams, and foundations

§         Or turned up to the top of the slab-on-grade or similar and then sealed to manufacturer's specifications

§         Meeting or exceeding the "Class A" performance standards in ASTM E-1745-97 (a/k/a American Society for Testing and Materials, "Standard Specification for Plastic Retarders Used in Contact with Soil Or Granular Fill Under Concrete Slabs")

§         Applied according to the more rigorous of manufacturer's specifications or ASTM E-1643 (a/k/a American Society for Testing & Materials, "Standard Practice of Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs"), or, if thermal insulation is desired, over Insul-Tarp (preferred)

§         Over not less than 2 linear inches continuous layer of coarsest sand

§         Over not less than 8 linear inches continuous layer of crushed gravel to 3 linear inches diameter

§         The top of face of which is not less than flush with the footing top of face

o       Tamped the greater compaction of

§         Not less than 50 beats per square foot and

§         95% density, modified proctor in conformance with not less than ASTM D-1557 (a/k/a American Society for Testing and Materials, "Substrate Tests for Moisture-Density Relations of Soils and Soil Aggregate Mixtures Using 10-Pound Rammer and 18-inch Drop")

§         For each layer, except the 8 linear inch of crushed gravel which shall be tamped in lifts of approximately 4 linear inches each 

§         Over earth substrate tamped damp (not wet) the greater compaction of these two

ü      Not less than 50 beats per square foot and

ü      95% density, modified proctor in conformance with not less than ASTM D-1557 (a/k/a American Society for Testing and Materials, "Substrate Tests for Moisture-Density Relations of Soils and Soil Aggregate Mixtures Using 10-Pound Rammer and 18-inch Drop")

§         In layers, or lifts, not greater than 6 linear inches depth 

Comment: The application of moisture and vapor barrier to exterior slabs-on-grade may appear wasted effort.  And it will be if a drainage plane is not applied in regard to slab pitch, slab substrates, and other subgrade drainage applications.  

·         A slab-on-ground exposed to weather and abutting structure shall slope down, evenly, uninterruptedly, and away from that structure at not less than ¼ linear inches/linear foot overall 

·         Slab-on-grade applications shall involve both control joints, or contraction joints, and isolation, or expansion, joints  

Comment:  The dear reader is encouraged to keep these two types of joints clearly and distinctly defined, since there is considerable cross-over or muddling of definitions in the literature and in practice, particularly in variously defining expansion joints as control joints and confusing construction joints (not addressed hereunder) with contraction joints. 

·         A slab-on-ground shall be thickened

o       To not less than twice surrounding placement and

o       #5 rebar reinforcement

o       At not greater than 16 linear inches on center grids and

o       Not less than 2 patterns of rebars continuous at top and bottom

o       In the following sites, among others

§         Below a fireplace, including chimney and hearth

§         Below a staircase foot

§         Below an interior bearing wall or column

§         Below an island, e.g., as in a kitchen island

§         Below a bathtub or whirlpool

§         Below a pool table

§         Below a major appliance 

·         A pitched slab-on-grade shall not be of excess volume in order to level its top of face;

o       Instead, the pitched slab-on-grade shall be demolished and

o       Removed from the site and

o       Replaced with a new slab-on-ground in a new-construction mode 

Comment: Please note that this last prescript does not prohibit applying an array of self-leveling products in conditions of out-of-true at narrow margins.  

·         Slab-on-grade

o       Compressive strength shall not be less than that of the

§         Principal footing and

§         Foundation stem wall and

o       May be more, e.g., as a garage slab-on-ground

o       Compressive strength shall not be greater than that of the slab-on-grade it extends or repairs

                Comment:  Beware that stucco weep screed is not enveloped in a placement.

[ Home ] [ Up ] [ Foundat'n Plan Design ] [ Foundat'n Plan Close ] [ Foundat'n Plan Closer ] [ Anchor Bolts ] [ Concrete Design ] [ Concrete Joints ] [ Drainage Slopes ] [ Footing Drain ] [ Foundat'n Pad ] [ Foundat'n Speak ] [ Foundat'n Strip ] [ Gas Curb ] [ Grade Beam ] [ Masonry Ledge ] [ Masonry Wythe ] [ Mod'd Grade Beam ] [ Pilasters ] [ Placement ] [ Radon Mitigation ] [ Rebar Reinforced ] [ Reinforced Corners ] [ Scored Concrete ] [ Slab-On-Ground ] [ Stone Water Table ]