Crack Repairs

Megapoxy categorises concrete cracks by cause and severity not just how the crack looks on the surface. Hairline cracks are minor, surface-level, and typically caused by impact shock or thermal attrition during curing. Megapoxy HX handles these with a simple capillary action repair.

Shrinkage cracks are similar in scale but caused by the concrete shrinking as it cures, treated the same way with Megapoxy HX or H. Settlement cracks run deeper, caused by ground movement beneath the slab, and call for Megapoxy HX or H via capillary repair for surface-level damage, or crack injection for anything deeper.

Structural cracks are the most serious: large, with visible depth, genuinely threatening load-bearing capacity, and they need the full Megapoxy Crack Injection Repair System, with Megapoxy PM handling the balloon bonding and sealing. Whether the crack compromises structural integrity is what differentiates a capillary-action or patching job from a full injection repair.

All concrete cracks need repairing because the size at the surface doesn’t predict what happens underneath. Left untreated, even a hairline crack can spread and lead to more severe damage over time. Whether it’s a fine hairline crack sealed by capillary action or a structural crack filled by full pressure injection, the goal in every case is stopping a small problem from becoming a much larger and more expensive one.

A Concrete Surface Profile is an industry-standard measure of surface roughness, developed by the International Concrete Repair Institute (ICRI), running from CSP 1 (nearly flat, acid-etched) to CSP 10 (heavily scarified and rough). Every repair system from sealers, high-build coatings, self-levelling toppings, polymer overlays to structural repair materials need different surface textures to bond properly, and matching the right CSP to a product is one of the strongest predictors of a durable, long-lasting repair. Megapoxy’s approach is to find the CSP your chosen product requires, then select the preparation method that achieves it.

Mechanical profiling, grinding, shotblasting, or scarification, is the preferred and safest option for roughening concrete ahead of a repair. Acid etching can work for some coatings, sealers and toppings, but it can be difficult to rinse and neutralise completely, it needs a well-ventilated work area, and it won’t touch petroleum-based contaminants or animal and vegetable oils sitting on the surface. More aggressive mechanical methods such as flame blasting, scabbling, or rotomilling can also cause micro-cracking, which then needs its own additional preparation before the repair goes ahead.

The Megapoxy Crack Injection Repair System is a controlled pressure-injection method that fills a structural crack from the inside out, rather than only sealing the surface. Megapoxy PM bonds injection balloons to the concrete along the length of the crack, spaced roughly 200–300mm apart (closer for narrower cracks), and once that’s fully sealed and cured, Megapoxy H or HX (depending on the severity of the crack) gets pumped into each balloon in turn. It’s a highly visual system and every balloon should remain inflated once its section of the crack is completely filled, so a deflating balloon with no visible leak simply means that section needs more resin. The whole process works even in vertical, overhead or hard-to-access areas, and is designed to restore real structural integrity in load-bearing elements, not just stop water getting in.

Down to 0.1mm. Megapoxy HX is the low-viscosity option built for fine cracks and deep penetration, while Megapoxy H handles crack widths from 0.5mm upward. That range allows the injection system scale from hairline structural cracks to much wider damage. Get in touch with our team to discover which solution is right for you.

An injection balloon leaking during the crack injection process can happen and doesn’t mean the process has failed. A small pinhole leak can occur where Megapoxy PM was used to seal the balloons over the crack. If that happens, turn off the balloon, disconnect the injection gun, and release pressure by opening the tap so the balloon deflates. Once any leaked resin is wiped away, a liberal coat of Megapoxy PF (rapid-set paste) over the leaking area sets in around 30 minutes at 25°C, after which injection can resume as normal.

For wide, shallow cracks that don’t threaten structural integrity; the kind you’d find across a floor or wall repair for instance, Megapoxy P1 and HT are the best patching solution. The process starts by cutting a clean V-groove along the crack, roughly 10mm deep on each side and 10mm across, then running a concrete cutting blade along the length to open it up slightly and expose fresh concrete to bond to. Mixed Megapoxy P1 gets worked into the prepared groove with a trowel, small tool or gloved hand, then smoothed level with a lightly moistened trowel. It’s a surface-only repair, not a structural one, but done properly it restores a durable, sealed, flush finish.

It uses the crack’s own capillary action to draw epoxy resin below the surface, rather than trying to force it in. A solvent like methylated spirits or acetone gets painted onto the crack first, and while it’s still wet, a generous coat of mixed Megapoxy H or HX is brushed directly over it; the resin follows the solvent down into the crack as it evaporates. The visible sign it’s worked is a darker, shinier film along the crack line once cured and running the process a second time without solvent, until there’s no visible ridge along the crack edges, confirms the resin has penetrated below the surface to properly bridge and seal it.

Megapoxy P1 is built specifically for this. A minimum 3mm layer of P1 applied directly to grit-blasted steel provides moisture protection roughly equivalent to 50mm of concrete cover when the original cover has been lost to damage or was never thick enough in the first place. The process starts by grinding the concrete back to a fresh, rough finish (typically CSP 3 minimum) and the exposed steel to a bright, shiny finish, before a thin film of P1 is worked into both surfaces and left to cure. A second coat is then trowelled on to a minimum 3mm thickness within 24 hours and smoothed level restoring both the physical cover and removing the immediate corrosion driver. Where spalling is widespread or chloride-driven, a localised patch addresses visible damage but doesn’t necessarily stop corrosion continuing in the surrounding concrete.

Concrete spalling also commonly referred to as concrete cancer starts with corrosion of the steel reinforcement inside a structure. Once moisture, chlorides or carbonation reach the rebar, the steel begins to rust, and rust occupies far more volume than the steel it replaces. That expansion puts the surrounding concrete under tensile stress that it wasn’t designed to resist, eventually cracking and pushing away the cover layer above it. Early signs are worth knowing before the damage becomes structural: hairline surface cracking that tracks the line of the reinforcement underneath, rust staining bleeding through the concrete and a hollow sound when the surface is tapped. By the time concrete visibly spalls away, the corrosion driving it has been active for a while which is why catching it at an early stage means a smaller repair with Megapoxy P1 instead of a larger rebuild.