The width and depth of the crack
Whether the crack is dormant or active
Whether or not appearance is a factor
Whether or not you need to seal against pressure
Concrete cracking is a frequent cause of complaints from homeowners. Cracking can be the result of one or a combination of factors such as shrinkage, thermal contraction, settlement or applied pressures. Cracks can be unsightly and a source of water intrusion. This is where finding the source or cause of the cracking comes into play.
Cracks that occur before concrete is fully hardened are due to shrinkage caused by the loss of water in the concrete mix. This is known as plastic shrinkage cracking.
Settlement cracks generally develop around embeds or around openings. It is not uncommon to first see a crack at the corner of a door or window or even near a beam pocket. Settlement cracks generally result from insufficient consolidation, dry mixes or lack of adequate concrete coverage over reinforcing steel.
Structural cracks in residential foundations usually result from settlement or horizontal loading or pressures. These types of cracks are much more prevalent in block basement walls. Generally hydrostatic pressure from water in the soil is the culprit. As more and more water builds the soil starts moving downward and outward. This outward movement applies great pressure on the wall eventually causing cracks.
Diagonal wall cracks that extend nearly the height of the wall are often a good indication of settlement. If structural cracks are suspected you should contact a professional engineer immediately.
Dormant or Active
Basement wall cracks that are determined to be no longer increasing are referred to as dormant cracks. Traditionally these cracks have been patched with cement grout or mortar. While this can be effective until water build up occurs or any unexpected movement occurs.
Active cracks, those judged to be still moving, require a sealant to be flexible if it is to be effective. Actively moving cracks need to be addressed carefully and completely.
Fine cracks may be sealed by injecting them with either a polyurethane grout or an epoxy resin. In recent years, epoxy resins have become the favored material, on dormant cracks, for this purpose and formulations are available which will penetrate cracks as fine as 0.1 mm in width, or less.
Epoxy grouts are widely used because:
They adhere strongly to both fresh and hardened concrete;
Formulations are available which will adhere to most surfaces and harden even under wet conditions
They have good mechanical strength and low shrinkage
They are resistant to a wide range of chemicals, including alkali’s
Epoxy grouts are normally injected under pressure. Nipples or injection points are fixed along the line of the crack and the surface is then sealed, on both sides of the cracked element. The epoxy is then injected under pressure, using specialized equipment. Once the epoxy hardens the repaired section often becomes stronger than original, hence the term concrete welding.
Wider cracks, i.e. those 1 mm or more in width, may also be sealed by injecting epoxy resin, particularly cracks on vertical surfaces. On horizontal surfaces it may be possible to simply pour the poly grout into the crack.
Other materials, such as polyurethane resins, have also been used satisfactorily to seal fine wall cracks. They can have lower viscosities than epoxies and, hence, can penetrate more easily. However, they generally do not achieve the same bond strengths.
Live cracks must be sealed with a flexible material, polyurethane, which can accommodate the movement in the crack. This is especially so when cyclic movements are anticipated. Flexible epoxy resins are available which will accommodate a small amount of movement but the more usual procedure is to choose a polyurethane, that remains flexible with wall movements.
As the technology of basement wall crack injection has grown the costs to perform this solution has decreased. Today’s crack injection professionals have very specialized equipment and specialized training which allows them to very quickly identify the best repair procedure and perform the injection at relatively low cost. There is no reason to wait any longer, the cracks will not fix themselves.