7 Best Epoxy Injection Kits for Void Filling

Structural voids in concrete—whether in foundation walls, slab-on-grade floors, or load-bearing pillars—compromise the long-term integrity of any building. Choosing the wrong epoxy for an injection repair often leads to material rejection, incomplete fill, or bond failure under thermal stress. Selecting a high-performance system requires matching the resin’s viscosity and mechanical properties to the specific geometry of the crack. This guide evaluates seven industry-standard kits to ensure the repair lasts as long as the concrete itself.

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Sika Sikadur 35 Hi-Mod LV: Pro’s Choice for Voids

Sikadur 35 Hi-Mod LV is the standard-bearer for gravity-fed or pressure-injected repairs in narrow cracks. Its extremely low viscosity allows it to penetrate hairline fissures that thicker epoxies simply bridge over.

This material excels where structural integrity is non-negotiable. When dealing with deep, vertical crack stabilization in foundation walls, the low viscosity ensures the product travels the full depth of the crack before curing.

The tradeoff lies in its runniness. Without proper surface sealing along the face of the crack, this epoxy will bleed out of every pinhole, leading to significant material waste and mess.

Simpson Strong-Tie ET-HP: Best for High Strength

Simpson Strong-Tie ET-HP earns its reputation in anchoring and high-load repair scenarios. It offers superior adhesive strength, making it the preferred choice when structural restoration requires high tensile and shear resistance.

When retrofitting a structure where seismic activity or high wind loads are a concern, structural-grade epoxies are non-negotiable. ET-HP cures into a high-modulus material that effectively bridges the gap and transfers loads across the crack.

Be aware that this is a high-strength epoxy, not a thin injection resin. It is best suited for wider voids or anchoring bolts where high viscosity is an advantage rather than a hindrance to flow.

PC Products PC-Concrete Gel: Best for Vertical Work

PC-Concrete Gel is designed for the reality of vertical surfaces. Its thixotropic properties ensure it stays put in a crack, even when working on a wall or a sloped soffit, without slumping or running.

This is the go-to solution for cosmetic repairs and sealing narrow gaps where gravity works against the installer. It functions like a thick paste, allowing the applicator to fill the void completely without worrying about the material exiting the bottom of the crack.

Because it is a gel, it is unsuitable for micro-cracks where deep, capillary penetration is required. Use this for surface-level repairs and structural patches where high flow is not a design requirement.

West System 105/205 Kit: Most Versatile System

West System is ubiquitous in marine construction for a reason. The 105/205 combination allows for an adjustable mix, enabling the user to tailor the consistency by adding fillers like silica or wood flour.

For a contractor managing varied repairs, this kit offers unmatched flexibility. Whether filling a hollow spot in a concrete masonry unit (CMU) or stabilizing a rotting timber header, the ability to control viscosity is a massive advantage.

The downside is the lack of pre-measured, high-pressure injection convenience. This system requires a more hands-on approach and is better suited for pourable voids rather than tight, pressure-injected crack repairs.

Abatron LiquidWood: Best Kit for Wood Restoration

While many epoxies are concrete-focused, Abatron LiquidWood is specifically engineered for wood fiber saturation. It penetrates deep into decayed wood, turning punky, soft fibers back into a rigid, structural material.

Use this when the structural void is located in a rotting window sill, a header, or a timber beam. It bridges the gap between a standard wood filler and a high-strength structural epoxy.

This is not for concrete. Using wood-specific resins in masonry voids will lead to bond failure, as these products are formulated to expand and contract with the natural movement of timber.

Crackbond LR-321 LV: Best Low-Viscosity Option

Crackbond LR-321 LV is formulated to be moisture-insensitive, which is a major benefit in damp basements or high-humidity environments. It remains liquid enough to travel deep into wet or damp cracks where other products might fail to adhere.

This low-viscosity resin is optimized for ease of use with standard pressure-injection pumps. It flows predictably, ensuring that even complex, winding crack paths are fully wetted out.

Reliability in damp conditions makes this an excellent choice for foundation repairs where external groundwater is a factor. Always ensure the crack is clear of loose debris, as even a moisture-tolerant epoxy cannot bond to loose dirt or standing sludge.

TotalBoat Thixo Fast Cure: Best for Quick Repairs

TotalBoat Thixo is the choice for time-sensitive jobs where a long cure time would hold up the rest of the project. Its fast-cure cycle allows for sanding, painting, or finishing within a few hours.

The nozzle system is specifically designed for ease of application, making it highly accessible for smaller, precise repairs. It is the perfect tool for finishing off punch-list items on a renovation site.

Do not expect this material to handle massive structural loads in the same way as an industrial-grade Sikadur or Simpson product. It is a high-performance adhesive, but it is not intended for heavy-duty structural pier injection.

Epoxy Viscosity: Low Medium or Gel for Your Job?

Understanding viscosity is the difference between a successful repair and a wasted day. Low-viscosity epoxies are for narrow cracks that need to be filled from the inside out; they flow like water to ensure full penetration.

Gel or high-viscosity epoxies are for structural patching or vertical work where you need the material to stay in place. Using a thin resin for a large, open void will result in the material running right through the crack before it ever begins to set.

If you are unsure of the crack width, start by performing a test pour or checking the crack with a feeler gauge. An incorrect viscosity choice leads to massive waste, as the material will either refuse to enter the gap or pour straight through it.

Surface Prep: The Key to a Permanent Epoxy Bond

Epoxy will not stick to dust, oil, or loose concrete. A pressure-injected repair requires a clean surface, which means using a wire brush, vacuum, or compressed air to remove all contaminants from the crack path before the injection ports are set.

If the surface is oily, use a degreaser and allow for complete drying. If the concrete is dusty, the epoxy will bond to the dust, not the concrete, leading to a “peel-off” failure under load.

A common oversight is neglecting the face of the crack. You must seal the entire exterior of the crack with a surface-sealing paste before injecting; otherwise, the pressure you apply will simply force the epoxy out the front, defeating the purpose of the injection.

Injection Ports and Technique for a Full Fill

Injection ports must be spaced correctly based on the depth and width of the crack, usually every 6 to 8 inches. Always begin injecting at the lowest port and move upward.

Injecting from the bottom up allows the epoxy to displace air as it fills the void, ensuring there are no air pockets or “dry” spots inside the concrete. Once the epoxy begins to emerge from the port directly above the one being filled, cap the lower port and move the nozzle up.

Maintain steady, consistent pressure rather than sudden bursts. Sudden pressure spikes often cause blowouts in the surface seal, which forces the contractor to stop, re-seal, and wait for the paste to cure before continuing.

The effectiveness of any injection kit is entirely dependent on proper crack preparation and an understanding of the material’s flow characteristics. By matching the viscosity to the crack geometry and respecting the curing process, you ensure the repair is a permanent, structural fix. Always prioritize clean, dry surfaces and a bottom-to-top injection sequence to avoid trapped air and incomplete fills. Investing in the right system up front prevents the cost of repeat repairs later.