What is a backer rod and why is it used?

Q: What causes expansion joint failure?

Expansion joints fail due to the degradation of the sealant material (from UV or age), 'compression set' (where the sealant loses its ability to bounce back), or 'three-sided adhesion' (where sealant bonds to the bottom of the joint, tearing it apart when the joint moves). Failure allows water and debris to enter, causing damage to the joint edges (arris) and leaking into the structure below. Repair involves removing the old sealant and installing a new system with a bond breaker.

Q: What is a Hypalon bandage system?

A Hypalon bandage (such as the Sikadur-Combiflex system) is a high-performance sealing strip used over expansion joints and large cracks. It consists of a flexible Hypalon tape bonded to the concrete surface on either side of the joint using epoxy adhesive. The central strip remains unbonded, allowing it to stretch and move with the joint while staying completely waterproof. It is ideal for sealing joints with large movement where standard mastics would tear.

Q: What is Shore Hardness in sealants?

Shore Hardness measures the resistance of a material to indentation. For joint sealants, we typically look at Shore A. A low Shore A (e.g., 20) is soft and flexible, good for high-movement facade joints. A high Shore A (e.g., 40-50) is harder and tougher, suitable for floor joints that must withstand foot traffic or trolley wheels. Specifying the wrong hardness leads to either joint failure (too hard) or indentation damage (too soft).

Q: How deep should concrete cover be over rebar?

The 'cover depth' is critical for protecting steel rebar from carbonation and chloride attack. British Standards (BS 8500) typically recommend a minimum cover of 25mm to 50mm, depending on exposure conditions (e.g., marine environments require deeper cover). If the cover is too shallow, environmental agents reach the steel quickly, causing premature corrosion. In repairs, if we cannot achieve the original cover depth, we use specialized coatings or extra-dense repair mortars to provide equivalent protection.

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