A
One-Piece Wood Cap
Two-Piece Wood Cap
Stucco Cap Metal Cap rowlock brick or paver cap maSonry tieS at 2 ft. o.c. concrete-block or concrete wall weather-reSiStant wood Seat nailed or Screwed to SupportS p.t. 2x or 4x SupportS bolted perpendicular to wall at 2 ft. oc. or per capacity of finiSh Seat material
concrete-block or concrete wall rounded Shape promoteS drainage. Stuc co or wall continuouS over cap. for Stuc co detailS
See 118−119
malleable or other large waSher weather-reSiStant wood cap beveled on top for drainage drip cut in underSide of cap anchor boltS at 6 ft. o.c. minimum. concrete-block or concrete wall malleable or other large waSher weather-reSiStant two-piece wood cap; top piece beveled & with drip
anchor boltS at 6 ft. o.c. minimum.
Silicone coating for moiSture protection concrete-block or concrete wall
continuouS metal cap with drip edge faSten metal cap to wall at Side to prevent moiSture penetration of top flat Surface. concrete-block or concrete wall Masonry Cap Wood-Bench Cap anchor boltS at 2 ft. o.c. & receSSed fluSh into SupportS concrete-block or concrete wall
noteS
theSe detailS are for the topS of retaining wallS, which are uSually expoSed to the weather. wood capS will ultimately decay, So they are deSigned for relative eaSe of replacement. there iS not much point in moiSture barrierS, Since they will only trap rainwater againSt the wood. retaining- wall SurfaceS Should be protected from moiSture penetration to prevent damage from the freeze- thaw cycle. Seal with clear acrylic or Silicone, or waterproof with modified portland-cement plaSter or bitumen-modified urethane.
Preparation before pouring a slab is critical to the quality of the slab itself. The primary goals in preparing for a slab are to provide adequate and even support, and to control ground moisture.
Soil—Soil is the ultimate support of the slab. Soil must be solid and free of organic material. Some soils require compaction. In termite areas, the soil is often treated chemically. Verify compaction and soil treat- ment practices in your local area.
Gravel—Gravel is a leveling device that provides a porous layer for groundwater to drain away from the slab. A minimum of 4 in. of gravel is recommended. Gravel must be clean and free from organic matter. Crushed and ungraded gravels must be compacted. Graded gravels such as pea gravel composed entirely of similar-sized round particles cannot and need not be compacted.
Moisture barrier—Moisture barriers prevent mois- ture (and retard vapor) from moving upward into a slab. Six-mil polyethylene is common and works well in Detail A. Overlap joints 12 in. and tape the joints in
areas of extreme moisture. A more substantial
concrete-rated moisture barrier is necessary for Detail B because the moisture barrier is in direct contact with the concrete slab. Polyethylene may deteriorate within
Slab footingS at bearing wallS & columnS
See 23 & 24
expanSion jointS & control jointS
See 21b
radiant-heat Slab
See 25c
plumbing through Slab
See 25b Slab/baSement wall See 21c & d turned-down Slab footing See 22 & 23c garage Slab
See 24a & b, 25a
Slab reinforcing
See 21
Slab with deep footing
See 23a, b & d
slabs
A
Detail A Detail B concrete Slab Sand moiSture barrier gravel Sub-Soil Slab perimeter inSulation See 22ba very short period in this situation, and it is easily punctured during slab preparation and pouring. A more substantial concrete-rated barrier is a fiber- reinforced bituminous membrane, sandwiched between two layers of polyethylene.
Sand—Sand (shown only in Detail A), allows water to escape from concrete in a downward direction during curing. This produces a stronger slab. The American Concrete Institute recommends a 2-in. layer of sand below slabs.
backfill & drainage See 18b waterproofing See 18c baSement wall baSement wall expanSion joint if Slab poured in cold weather
Welded wire mesh—Welded wire mesh (WWM) is
the most common reinforcement for light-duty slabs. The most common size is 6x6 (w1.4 x w1.4)—adequate for a residential garage, which requires a stronger slab than a house. One disadvantage to WWM is that the 6-in. grid is often stepped on and forced to the bottom of the slab as the concrete is poured.
Rebar—Rebar is stronger than welded wire mesh. A grid of #3 rebar at 24 in. o.c is also adequate for a residential garage.
Fiber reinforcement—Fiber reinforcement is a re- cent development in slab reinforcement. Polypropylene fiber reinforcement is mixed with the concrete at the plant and poured integrally with the slab, thereby elim- inating difficulties with placement of the reinforcing material. The addition of 1.5 lb. of fiber per cubic yard of concrete produces flexural strength equal to WWM in a slab. The appearance of the slab is affected by the presence of fibers exposed at the surface.
Expansion joints—Expansion joints allow slabs to expand and contract slightly with temperature changes. They also allow slabs to act independently of building elements with which they interface. Expansion joints are appropriate at the edges of slabs that are not heated (not in the living space) or that, for some other reason, are expected to change temperature significantly over their lifetimes. Expansion joints are also used to isolate building elements that penetrate slabs such as struc- tural columns, walls, or plumbing (see 25B).
Control joints—Control joints induce cracking to occur at selected locations. They are troweled or cut into the surface of a slab to about one-quarter of the slab depth and at 20-ft. intervals. Cold joints, which automatically occur between sections of a slab poured separately, can act as control joints.