BEFORE THE ARCHITECT – CUSTOM HOME DESIGNING BACKGROUND – HOUSE DESIGN ARTICLES
ALL ABOUT HOUSE FOUNDATION PROBLEMS and YOUR HOME DESIGN FOUNDATION PLAN SLAB-ON-GRADE, OR SLAB-ON-GROUND
By Before The Architect Copyright 2009
With other guys, you can get the house plans they sold you. With us, you can get the house plans you know you paid for. Oscar Wilde had it that "a cynic is a man who knows the price of everything and the value of nothing." Oscar, we're not just talking cynics here. We're talking client rejects, too. Before The Architect
QUESTION: WHASSUP WITH HOUSE FOUNDATION PROBLEMS?
ANSWER: PRETTY NEAR NOTHING WITH A GOOD HOME FOUNDATION PLAN.
What About A Slab-on-Ground Home Foundation, or Slab-On-Grade Home Foundation?INTRODUCTION
· Before The Architect recognizes no more abused, less well understood subjects in house foundation concrete design, concrete details, and concrete construction than slab-on-grade design, slab-on-grade detail, and slab-on-grade construction.
· The following article is intended to address the basics of house foundation slab-on-grade design, detail, and construction matters generally. The central aspect of this address is the preparation of slab-on-grade substrates in regard to both materials and methods.
As with many foundation design elements, slab-on-grade is not without synonyms, e.g., (the surprisingly popular) slab-on-ground, slab, concrete slab, ground-supported slab, floor slab, monolithic slab, thickened slab, ground floor slab.
Comment: We are not talking post-tension slabs, a/k/a, among others, raft slab or waffle slab.
HOUSE FOUNDATION DESIGN DETAILS, SLAB-ON-GRADE - THE BASICS
· A slab-on-ground, grade beam, footing, raised curb, column, brick or masonry ledge, pilaster, and any other concrete foundation element
o Shall be applied in the field in a single, or monolithic, placement if at all possible and
o If not then, for foundations separating exterior and interior space
§ There shall be a continuous sheet of high puncture-resistant EPDM (Ethylene Propylene Diene Monomer)
§ Set at all cold joints between footing and wall
§ Before each successive placement
o When between slab-on-grade and pilaster top of face and slab-on-grade and grade beam top of face
§ There shall be a continuous sheet of high puncture-resistant EPDM (Ethylene Propylene Diene Monomer)
§ Set at all cold joints between both pilaster and grade beam and the slab
§ Before each successive slab placement
· A slab-on-ground
o May have a continuous 6 linear inches x 6 linear inches 10/10 welded wire fabric
§ At 2 linear inches below slab-on-grade top of face and
§ Lapped not less than 2 meshes at splices
o Which mesh shall conform to not less than ASTM A-185 (a/k/a American Society for Testing and Materials, "Standard Specification for Steel Welded Wire Reinforcement, Plain, for Concrete")
§ Which mesh may be severed every other strand at a joint
o In lieu, may have fiber pieces, shreds, and the like (but not steel fiber) reinforcement
Comment: This home designer personally objects to seeing little fibers sticking from a curing slab, and is entertained by the notion read somewhere of burning them off with a torch once initial curing is finished.
o Shall have continuous #5 rebar-Grade 50 spaced, unless otherwise noted
§ On a not greater than 16 linear inches grid
§ Which rebar shall be deformed
§ Which rebar shall be smooth or, if deformed, then
ü May be severed
ü Every other one
ü At a joint when crossing a contraction joint
§ Provided at the mid-height of the slab-on-ground and
§ In addition (not in lieu), may include other continuous, reinforcing material, such as, synthetic fiber reinforcement
Comment: Welded wire fabric, or welded wire mesh, or wire fabric, or electric welded wire mesh (a/k/a EWWM), shall not be a sole form of reinforcement. Indeed, many sources identify applications of mesh to slabs-on-grade as assisting against pad shrinking and resultant cracking and otherwise as being without significant reinforcement quality, if any at all. In other words, the mesh won't keep a slab from cracking; it'll only keep it from going to pieces.
Comment: Importantly - 6 linear inches x 6 linear inches 10/10 welded wire mesh or fiber mesh lifted into place approximately 1 linear inch below slab-on-grade top of face and not supported, in flat sheets and not rolls with sheets lapped not less than 1 square, or fiber, or both.
Comment: It's the placement that gets botched more often than not when mechanics stomp on the mesh to the slab-on-grade bottom, which is why, among reasons, that this home designer prefers fiber reinforcement wherewith no amount of stomping can botch the job.
o Shall float to house foundation walls and footings, i.e., shall not be barred or otherwise tied to foundation structure
o Shall have a bond break between it and foundation structure –
o Along the entire length of abut to foundation structure
o Shall include
§ Membrane
§ Isolation joint
§ Backer rod
§ Sealant
· For garage floors
o Shall not be less than 6 linear inches thick
o Shall be not less than 4000 pounds compressive strength 28 days after placement
o Shall be reinforced with
§ Not less than #5 rebar
§ On not greater than 12 linear inches centers
o Which rebar shall be deformed in the field
o Which rebar when crossing a contraction joint–
§ May be severed every other one at the joint crossing or
§ Shall be sleeved or
§ Shall be smooth
o Shall float
§ If wider than 2 bays
§ Shall have a grade beam the entire width (not depth) of the bays at mid-length
· For exterior slabs on grade other than driveways
o Shall not be less than 4 linear inches thick
o Shall be reinforced with
§ Not less than #5 rebar
§ On not greater than 24 linear inches centers
o Which rebar shall be deformed in the field
o Which rebar shall be smooth or sleeved when crossing a contraction, or control, joint
o Shall float
§ If wider than 16 linear feet
§ Shall have a grade beam the entire width (not depth) at mid-length
o Shall not be less than 4 linear inches depth in the field
o Shall be at its edges
§ Not less than 6 linear inches thick
§ For not less than 8 linear inches width
o Shall be reinforced with
§ Not less than #5 rebar at
§ Not greater than 24 linear inches on center both ways
o Which rebar shall be deformed in the field
o Which rebar may be
§ Severed every other one at a joint or
§ Sleeved or smooth when crossing a contraction, or control, joint
o Shall be placed
§ With water-to-concrete ratio of 0.45
§ Which placement shall be air-entrained at 6%
o Shall have cover on the horizontal not less than 3/4 linear inch plus aggregate size
Comment: A 4 linear inch thick slab-on-grade may be challenged for cover when two #5 rebars cross within 5/8 linear inch maximum aggregate diameter further within not less than ¾ linear inch concrete cover to top of face and bottom of face of the slab-on-grade. This home designer knows that foundation crews’ll thicken the slab-on-grade some at such areas. Indeed, reputedly successful foundation contractors customarily place 6+ linear inch thick slabs, even with two layers of rebar webs.
Reinforced Concrete Slab-On-Ground with Substrates, Section
Comment: Note well that this order of layering may not go well with some, particularly in the upper-end arrangement of the cross-laminated poly, the application of it and not regular poly sheeting, the membrane's unbonding to placement by crusher run cover, and sand below the membrane. Both materials and methods are equally important in this designer's opinion.
Comment: Please note, dear reader, that in all instances,
sub-slab-on-grade foundation elements are continuously separated at their top of
face from the bottom of face of a slab-on-grade by a continuous bond break.
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