The term “fixing cracks” is a bit misleading since there is no way to “fix” cracks in concrete, only fill them. The proper term to use when treating cracks prior to placement of a decorative overlay is “bridging.” This is accomplished by filling or covering the crack with a rigid material so it becomes flush or slightly higher in elevation than the surrounding surface. (Avoid soft, flexible crack fillers.)
There are two types of joints in concrete slabs, Expansion Joints and Control Crack Joints. Every concrete slab, inside or outside are required to have joints every eight feet horizontally and vertically.
Expansion Joints provide space between concrete slabs as a buffer for expansion on hot days and contraction when it is cold. Usually these expansion joints are installed during the initial installation of the concrete and are made of wood or some soft material so they can move with the expansion and contraction of the concrete. These joints vary in size from half-inch to an inch in width and three to four inches in depth. A slab without expansion joints will crack which will reduce the life of the concrete slab. These joints will crack all the way to the bottom of the concrete. If they come open, water will be allowed to run under the bed of the slab, eroding it and creating voids which during harsh winter conditions can heave and cause major cracks and displacement in the concrete. Open joints can also be point of deterioration of the concrete because of the freeze-thaw effect.
Control Crack Joints allow cracking in a controlled area as the slab settles with time. Usually these joints are cut into the slab after the concrete hardens. Control crack joints vary in size from one-eighth inch to one-quarter inch in width and half inch in depth. A slab without these joints will crack in random patterns which ruins the look of the concrete as well as allows for damage from water intrusion and freeze-thaw which will reduce the life of the slab.
Both type of joints will accumulate dirt and debris, allow grass or weeds to grow, and allow water to filter under the slab, etc. Water under the slab accelerates the settling of the concrete slab creating uneven concrete surfaces and cracks. Fortunately, there is a way to repair, and even prevent, these cracks from harming your floor:
- A sealer is soft and able to accommodate the concrete slab’s expansion and contraction. The sealer’s purpose is to prevent water, ice, and dirt from getting into the joint (and into the subgrade) and to prevent intrusion from below the slab-including of radon. Sealers can also improve the appearance of floors and slabs.
- A filler is a rigid material that supports the edge of the joint when heavy traffic crosses. This type of material is only effective with saw-cut joints; rounded tooled edges can’t support the filler.
- Both sealers and fillers should only be installed after the slab has had a chance to shrink as much as possible. Fillers are only effective if installed after the concrete has gone through most of its shrinkage, although that can take a year or more. Fillers and sealers should be checked at the end of the first year of service and repaired or replaced as needed.
- Effective sealant materials must bond to the concrete, be impermeable, and be able to handle the expansion and contraction.
- Before installing a sealant, the joint must be dry and free of dust and debris. Vacuum it thoroughly before sealing. Carefully follow the sealant manufacturer’s installation instructions.
- For sealers, use a bond breaker or backer rod in the bottom of the joint. This prevents the sealer from sagging into the joint and from adhering to the bottom of the joint, which allows the sealant to stretch on both the top and the bottom.
- A backer rod in the joint also keeps the sealer plug thinner, reducing the amount of sealant needed.
- Reduces Cracking
- Prevents water from running below concrete creating voids
- Eliminates the accumulation of dirt, salt, and other foreign materials
- Prevents weed and grass growth
- Prevents breakage from creating trip points
- Humidity Retention – Reduced Ground shifting
- Bonds to concrete for long service life – will expand up to 1″ before breaking
- Prevents water from getting to rebar and creating rust
- Easier to clean
- Improves appearance of property
- Easier to remove ice and snow
- Reduces damage from freeze/thaw expansion and contraction