Construction joint are a weak point in building design and a common entry point for termites. Protecting these joints is a must in pre-construction termite treatments.
Australian Standard 3660.1 New Building Work identifies that a concrete slab constructed to AS 2870 or AS 3600 can be used as a component of the termite management system. When built to Australian Standards concrete is a hard and durable material.
It can withstand all kinds of weather conditions, is easy to maintain, and will last the life of the building. Unfortunately, its strength can also be its weakness. Concrete cannot stretch and bend because it is not flexible. When the concrete expands and contracts because of external pressures, it may unavoidably crack under the pressure and can become weak. The only way to avoid this is to add joints to the concrete.
Concrete joints are engineered and placed strategically in the concrete to compensate for the expansion and contraction of the material. Concrete joints may also be installed to isolate the concrete slab from other types of wall systems thus the concrete slab will be independent of the structures surrounding it, so any expansion and contraction will not have an impact on them.
Types of Construction Joints in Concrete
Contractors can install different kinds of joints based on the engineer’s requirements. A concrete slab can have different kinds of joints.
• Construction joints, which includes keyed joints, dowelled joint and butt joints, are placed to keep new concrete in place and are essentially screed rails made from wood, metal, or plastic and are placed during the pouring and finishing of concrete. The construction joints will allow you to pour the concrete in steps and control the slab placement according to your requirements.
• Saw cut joints or trowelled joints – are a sawed, formed, or trowelled tooled groove in a concrete slab that creates a weakened vertical plane. It regulates the location of the cracking caused by dimensional changes in the slab. They are added to the surface as the concrete settles and before it has a chance to form cracks. The contractors will create cracks in the direction they desire to control it and preserve the structural integrity of the concrete. The saw cut joints are typically 6 mm wide and a minimum of 25 mm deep
• Isolation joints – As the name suggests, this joint exists to isolate the concrete slab from the surrounding constructions. When the concrete slab expands or contracts, the isolation joints will ensure the slab does not crack or cause any problems to nearby pipes, pillars, walls, and columns.
Obviously, joints in slabs may result in concealed termite entry points, therefore all types of slab joints require termite proofing. The method of termite proofing is usually dictated by the joint type itself.
Termseal have various methods in preventing termite ingress through slab control joints. The preferred option is to address the top of the joint using Termseal Prime Coat, Sealant Active, Multi-Purpose and Reo-Band.
This method can only be installed if there are walls or floor coverings such as tiles or carpet to cover the construction joint and treatment. When dealing with saw cut joints which are typically exposed or joints that are not able to be concealed, such as polished concrete floors, are easily addressed by the application of Termseal Prime Coat and Sealant Active in the joint
Butt Joints or Cold Joints, where new concrete is poured up to existing concrete or existing walls can also be treated in various ways using Termseal products and methods. One such application is the use of Termseal Ura-Fen TWB which is nailed and adhered to the existing structure and placed under the new concrete slab. Pest managers could also use one of the other methods described above.
Termseal do not recommend the use of sheet materials that are placed on the builders plastic directly below the construction joint especially on in fill slabs due to the possibility that the in fill soils will subside over time and thus create a void between the termite barrier material and the underside of the concrete slab, thus allowing termite entry. Selecting the appropriate product for the type of construction joint is critical. With five products capable of protecting all types of construction joints, all developed and manufactured here in Australia, Termseal has you covered.
Barry Quon, National Technical and Training Manager, Termseal