Concrete Specialties - Expansion Joint
All concrete, once placed, will contract slightly during the curing process; this is the primary cause of small surface cracks that appear during the curing process. When set, concrete will expand and/or contract slightly with ambient temperature. It is therefore advisable to incorporate some form of movement joint within larger slabs.
The usual spacing recommendation for joint in a non-reinforced slab is a separation of approximately 30 times the slab thickness. For example a 4” thick slab x 30 = 120” or a joint every 10’ 0”. Joints can be positioned within a slab for aesthetic reasons or can be centered.
Expansion Joints allow expansion AND contraction of a concrete slab without generating potentially damaging forces within the slab itself or the surrounding structures.
Hamilton Builders’ Supply Inc supplies 2 types of Expansion Joint fillers:
- A fibrous, compressible, flexible board, such as 'Flexcell' or “Fibre Expansion Joint” is readily available in pre-cut strips ½” thick x 4”, 5”, 6”, and 8” widths x 10’ 0” long.
- DECK-O-FOAM Expansion Joint Filler is a flexible, lightweight, non-staining, polyethylene, closed-cell expansion joint filler. It is a chemical-resistant, ultraviolet stable, non-absorbent, low density, economical, compressible foam. Crack Control Joints are most commonly used on Concrete or Stamped Concrete Paving, particularly residential driveways and patios.
Crack control joints are designed so that when the concrete does crack, it cracks in a predictable manner at a precise location. Sawn joints are normally cut between 25% and 33% of the depth of the slab and one week or more after sealing, so that the concrete will have had a reasonable amount of time to cure and avoid 'spalling' at the cut edges, and for the sealant to protect the surface from the concrete dust.
Joints Sealants are used for caulking and sealing joints subject to concrete movement to provide a firm, flexible, weather-tight seal.
* See the Hamilton Builders’ Supply web page on SEALANTS for choices on premium grade, high performance sealants.