Sikadur epoxy is a family of two-part structural adhesives made by Sika, one of the largest construction chemical manufacturers in the world. If you are staring at a cracked garage slab, a loose piece of rebar, or a concrete step that has separated from its footing, Sikadur epoxy is often the product a contractor reaches for because it bonds concrete to concrete, steel to concrete, and rebar into drilled holes with genuine load-bearing strength.
Unlike hardware-store epoxy putty, the Sikadur line is engineered for structural repair. That means it has published bond strengths, tensile values, and pot-life ratings you can actually design around. This guide breaks down the main variants, how to mix and apply them, what they cost, and when the job is realistic for a DIYer versus a case for a professional.
What Sikadur Epoxy Is Used For
Sikadur products are moisture-tolerant, high-modulus epoxies that cure to a bond stronger than the concrete around them. In most structural repairs, when the joint fails again it fails through the concrete, not through the epoxy line. That is exactly the behavior engineers want.
Typical residential and light-commercial applications include:
- Crack injection in foundation walls, slabs, and columns to restore monolithic strength and seal against water.
- Anchoring and doweling rebar, threaded rod, or bolts into drilled holes in concrete.
- Bonding fresh concrete to hardened concrete, such as pouring a new curb or step against an existing slab.
- Grouting baseplates and filling voids where structural contact is required.
Because these are structural products, they are not the right choice for cosmetic surface coating or decorative flooring. Sika sells separate coating lines for that purpose.
The Main Sikadur Epoxy Variants
Three products cover the vast majority of home-scale work. Choosing correctly comes down to viscosity, which controls how the epoxy flows into a gap.
Sikadur 31 Hi-Mod Gel
This is a thick, non-sag paste, roughly the consistency of stiff peanut butter. Because it will not run, it excels at vertical and overhead repairs, patching spalls, bonding pieces back together, and setting anchors where you do not want the material draining out of the hole. It typically comes in a 1-gallon unit (Part A and Part B combined) for around $70 to $110.
Sikadur 32 Hi-Mod
A medium-viscosity bonding agent designed specifically to bond plastic (fresh) concrete to hardened concrete and to bond hardened concrete to steel. If you are pouring new against old, this is the intended product. Expect roughly $90 to $140 per gallon unit.
Sikadur 35 Hi-Mod LV
The “LV” stands for low viscosity. This thin, water-like epoxy is formulated for pressure and gravity crack injection because it wicks into hairline cracks a thicker product could never reach. It is also used as a pre-mix binder for epoxy mortars. A gallon unit runs about $100 to $160.
Mix Ratio, Pot Life, and Cure Time
Every Sikadur product ships as a pre-proportioned Part A (resin) and Part B (hardener). The mix ratio is fixed by the packaging, most commonly around 2:1 or 3:1 by volume, and you should never guess or “eyeball” a partial batch. Mixing off-ratio is the single most common cause of a repair that stays tacky and never fully cures.
Key working numbers to plan around at roughly 73 degrees Fahrenheit:
- Pot life: approximately 20 to 40 minutes depending on the product and batch size. Larger masses generate more heat and kick faster.
- Tack-free / initial set: several hours.
- Full structural cure: about 7 days for maximum strength, though many products reach serviceable strength in 1 to 3 days.
Temperature matters enormously. Below about 40 to 50 degrees Fahrenheit, cure slows dramatically or stalls; in hot weather pot life shrinks, so mix smaller batches. Always read the specific product data sheet (PDS) for the exact figures, because they differ between Sikadur 31, 32, and 35.
How to Mix and Apply Sikadur Epoxy
- Prep the surface. Concrete must be sound, clean, and free of dust, oil, curing compounds, and loose material. Roughen smooth surfaces to a sandpaper-like profile. The epoxy can tolerate a slightly damp surface, but standing water must be removed.
- Combine Part A and Part B. Pour the entire hardener into the resin (or the full pre-measured portions) and mix with a low-speed drill and paddle for about 3 minutes until the color is completely uniform with no streaks.
- Apply within the pot life. For bonding, scrub a thin coat onto the substrate. For anchoring, fill the hole and insert the rebar with a twisting motion to eliminate air pockets. For injection, use ports and a pump for Sikadur 35.
- Protect and cure. Do not disturb the repair, and keep it within the recommended temperature range until it reaches structural cure.
Wear nitrile gloves and eye protection. Uncured epoxy is a skin sensitizer, and repeated unprotected exposure can cause allergic reactions.
Sikadur Epoxy Cost and Coverage
Pricing varies by variant and retailer, but a single gallon unit of Sikadur epoxy generally falls between $70 and $160. Coverage depends entirely on the job. As a bonding agent brushed at a thin coat, a gallon can cover well over 100 square feet. Used to fill anchor holes or a deep crack, the same gallon disappears quickly because you are filling volume, not coating area.
For a small home repair, such as setting two or three anchors or bonding a single cracked step, one gallon or even a smaller cartridge is usually plenty. Buy the correct viscosity rather than the cheapest option, since using a gel where you needed a low-viscosity injection product will simply fail to penetrate.
DIY Versus Hiring a Professional
Straightforward tasks are within reach of a careful DIYer: bonding a broken concrete step with Sikadur 31, anchoring a railing post, or patching a spall. The materials are forgiving as long as you respect the mix ratio and pot life.
Call a professional when the repair is genuinely structural, such as active foundation cracks, load-bearing columns, or any situation where an engineer’s stamp may be required. Crack injection in particular is easy to do badly; a pro has the pumps, ports, and experience to fill a crack completely rather than just capping the surface. If the failure could affect the structural integrity of your home, the cost of doing it once, correctly, is far lower than doing it twice.
Common Mistakes to Avoid
Even with a forgiving product, a handful of errors cause most failed Sikadur repairs. Avoiding them costs nothing and saves you a do-over.
- Skipping surface prep. Epoxy will not bond to dust, laitance, oil, or a curing compound. A quick pass with a wire brush and a vacuum, or a grinder on smooth concrete, is the difference between a permanent bond and a peel-off patch.
- Splitting a unit off-ratio. If you only need part of a kit, you must measure Part A and Part B by the exact ratio on the label using separate containers. Guessing leaves a rubbery, uncured mess.
- Under-mixing. Streaks of un-blended resin never cure. Mix a full three minutes and scrape the sides and bottom of the container.
- Ignoring temperature. Applying in the cold or in direct summer sun changes cure and pot life dramatically. Work in the 50 to 85 degree Fahrenheit window when you can.
- Trapping air in an anchor hole. Inject epoxy from the bottom up and twist the rod as you insert it so trapped air escapes rather than creating a weak void.
Storage and Shelf Life
Unopened Sikadur components have a shelf life of about two years when stored in a cool, dry place between roughly 40 and 95 degrees Fahrenheit. If the resin has crystallized or thickened in storage, gently warming the container to room temperature usually restores it. Never mix components from different product lines together, and once Part A and Part B are combined there is no pausing the reaction, so plan the whole job before you open the kit. Keep partially used kits tightly sealed and away from moisture, which can compromise the hardener over time.
Final Thoughts on Sikadur Epoxy
Sikadur epoxy gives homeowners access to the same structural-grade adhesives contractors rely on, provided you match the product to the job: gel (Sikadur 31) for vertical and overhead patching and anchoring, medium viscosity (Sikadur 32) for bonding new concrete to old, and low viscosity (Sikadur 35 Hi-Mod LV) for crack injection. Respect the fixed mix ratio, work inside the pot life, and give the repair a full week to reach maximum strength. Match the viscosity to the gap, follow the product data sheet, and you will get a bond that outlasts the concrete around it.
