What is Crack Chasing?

Crack chasing is the preparation stage of a crack repair. A crack in concrete or asphalt is a rough, tapering, contaminated void of no consistent width, and no sealant will bond reliably to that. Chasing cuts it out into a clean rectangular reservoir of known width and depth, which is a shape a sealant can actually work in.

Three reasons, and they are the reasons crack repairs fail. First, the faces are contaminated with dust, oil, water and vegetation, so a sealant has nothing sound to bond to. Second, the width varies along the crack, so the sealant is over-extended in the narrow parts and under-supported in the wide parts. Third, and most importantly, a crack moves. A sealant needs a designed width-to-depth ratio to accommodate that movement without tearing, and an unchased crack does not offer one.

Pouring sealant into a raw crack produces something that looks repaired and fails in the first cold snap. The material has not failed. It was never given a joint to work in.

A chasing machine, essentially a saw with a set of cutting wheels, is run along the crack line to route it out to a consistent width and depth. Depth and width are chosen for the movement expected: the reservoir has to be deep enough to hold sealant that can stretch and shallow enough that it is not wasting material.

The reservoir is then cleaned out, usually by compressed air or vacuum, and has to be genuinely dry before anything goes in. Where the crack is live and moving, backer rod is set to the correct depth so the sealant bonds on two faces only and is free to move on the third. Sealant bonded on three faces tears itself apart.

Chasing is almost never a visit of its own. It is the operation immediately before sealing, and on roads and airfield pavements it is usually followed by overbanding, which lays a band of hot applied material over the sealed crack to waterproof it and take the traffic wear.

Where the chase is carrying a cable rather than a sealant, the technique is similar but the tolerances are not: see what a cable chase is.

We are based at Little Westerhill Farm near Maidstone in Kent. Kent, London, Sussex, Essex and the wider South East are covered from our own yard, and longer programmes are mobilised UK wide. For the service itself see crack chasing.