Concrete Adhesives & Sealants

Most failed bonds aren’t a product problem. They’re a chemistry-matching problem. Concrete adhesives bond concrete to itself or to other materials — steel, glass, wood, and plastics. The trick is matching the adhesive to what the joint has to carry, how much it’ll move, and how wet it gets. Pick wrong and you’re chiseling out a failed repair next spring.

Here’s the short version for a contractor or serious DIYer standing at the counter: epoxy for rigid structural strength, polyurethane for flexibility and moisture, hybrid (MS polymer) when you want one product that does most things, acrylic for fast light-duty interior work, and silicone strictly for sealing. That’s the whole decision tree. Everything below is detail.

The Five Chemistries and What Each Does Best

Five families cover nearly every concrete job. They sort by how much they flex and how much load they hold.

Epoxy is the heavy hitter. Known for high strength and excellent resistance to harsh environmental conditions, epoxies are ideal for bonding concrete to concrete or concrete to other materials such as steel and plastics. They’re typically two-part systems, consisting of a resin and a hardener. The bond strength is high, often exceeding 30 MPa in shear strength. They also offer excellent resistance to water, chemicals, and temperature fluctuations, making them suitable for both indoor and outdoor applications. The catch — epoxy adhesives tend to be rigid once cured.

Polyurethane trades some raw strength for flex. Polyurethane adhesives offer flexibility, which is essential when bonding materials that expand and contract at different rates, such as concrete and steel. They’re also resistant to moisture, making them ideal for outdoor or submerged applications. Unlike epoxy, polyurethane adhesives are more flexible and can absorb shock and vibration. That flex matters in Montana, where freeze-thaw cycling pulls joints apart and back together all year.

Hybrid (MS polymer) splits the difference. Hybrid adhesives combine the best qualities of both epoxies and polyurethanes, offering the strength and durability of epoxies with the flexibility and resilience of polyurethanes. They’re particularly useful when bonding concrete to materials that undergo frequent thermal expansion or contraction, and offer excellent resistance to moisture, UV rays, and chemicals.

Acrylic is the fast worker. Acrylic adhesives provide a fast-curing bonding solution and are particularly useful for applications that require quick assembly or turnaround. They bond concrete to metals, plastics, and glass with quick setting time, and resist UV degradation well — though they may not offer the same tensile strength as epoxies or polyurethanes. Good for interior decorative work, not load-bearing.

Silicone seals. It doesn’t bond structurally. Use it for joints, period.

Chemistry	Strength	Flexibility	Best for
Epoxy	Highest (30+ MPa shear)	Rigid	Structural loads, anchoring, concrete-to-concrete
Polyurethane	Moderate	Flexible	Movement joints, damp/submerged work, porous surfaces
Hybrid (MS)	High	Flexible	All-around bonding across temperatures
Acrylic	Light-medium	Moderate	Fast interior decorative tasks, UV exposure
Silicone	Sealing only	High	Joint sealing — not structural bonding

Structural vs. Non-Structural — Know What the Joint Carries

This is the line that separates a safe load-bearing repair from a decorative one. Get it wrong and the joint fails under load.

Structural adhesives give at least 5 to 8 MPa tensile shear strength. They’re required for structural parts — bonding concrete to concrete, ceramic tiles to concrete, masonry, construction panels, outside doors, sealing metal parts into concrete, composite bonding, metal bonding, and structural glass. These adhesives may be epoxy adhesives, structural polyurethanes, silicones, and structural acrylics.

Non-structural is the lighter side. Non-structural adhesives bond decorative materials, such as floor and wall coverings, and other materials which don’t need very high strength — panels, fibers and particle boards, trim, some interior doors.

When the spec sheet matters, look for verified numbers. The serious structural epoxies conform to ASTM C-881. To put real-world strength in perspective: Euclid’s DURAL 617NS tests at “Breaks concrete” for concrete bond strength under ASTM D4541 — meaning the concrete itself fails before the adhesive lets go. That’s the standard you want for a load-bearing bond.

Matching the Task to the Right Adhesive

Most folks show up with a job, not a chemistry. Here’s how common concrete tasks map to products.

Anchoring rebar, bolts, and dowels. Reach for a high-viscosity, non-sag epoxy gel. W.R. Meadows’ REZI-WELD GEL PASTE is a high viscosity, rapid setting, thixotropic, structural epoxy anchoring/bonding adhesive. It provides high mechanical properties and bond strength to concrete, is moisture-insensitive, and can be troweled, brushed, injected, or pumped. It’s used to secure metal anchors, bolts, rebar, and dowels in hardened concrete. On embedment depth, DURAL 617NS gives the rule of thumb: embedment depth 10 to 15 times bolt diameter.

Injecting non-moving cracks. Use a low-viscosity injection epoxy. REZI-WELD LV is a very low viscosity, two-component, moisture insensitive, high strength, high modulus structural injection epoxy resin, designed for gravity feeding or pressure injecting into non-moving cracks in hardened concrete to reinstate structural integrity. It can be applied by pressure injecting using two-component metering systems, hand-held bulk guns, or pressure pots, and is suitable for fine, non-moving structural cracks for long-term repairs.

Paver caps, masonry veneer, faux stone, door sills. This is flexible polyurethane territory. SikaBond Construction Adhesive is a one-component, durable and flexible exterior polyurethane adhesive with excellent adhesion on all cement-based materials, brick, ceramics, glass, metals, and wood. It runs 225 psi tensile strength (ASTM D-412) and handles paver caps, masonry veneer and faux stone, submerged applications like ponds, net tile installation, floor moldings and door sills, lightweight construction materials, and wood or metal window and door frames. It also can be used to fill in gaps.

Bonding fresh concrete to hardened concrete or steel. A moisture-insensitive epoxy applied while tacky. DURAL 617NS is a multi-purpose, moisture insensitive, solvent-free epoxy structural adhesive used to bond concrete to concrete, steel to concrete, and fresh concrete to cured concrete. The method matters here: apply onto solid surfaces and place fresh concrete while adhesive is still tacky. If adhesive becomes glossy and loses tack, remove and recoat. And keep that bond line tight — glue line not to exceed 6mm.

A note on the Montana angle: that SikaBond polyurethane is rated waterproof and water immersible after cure, remaining flexible to absorb movement. Its service temperature runs -40 to 170 °F. For damp foundations, ponds, and anything seeing snowmelt, that flex-plus-moisture combo beats a rigid epoxy that’ll crack under repeated freeze-thaw.

Surface Prep, Mixing, and Temperature

The right adhesive still fails if the prep is sloppy. This is the most preventable cause of a blown bond.

Prep clean, prep rough. Surfaces have to be sound and contaminant-free. For DURAL 617NS: surfaces must be clean, sound, dry or damp, but free of standing water. Exposed concrete must be sandblasted or chipped to show well-bonded aggregate. Steel should be grit blasted clean, free of rust, paint or foreign matter. Sikadur-31 says the same in different words — surface must be clean and sound, may be dry or damp but free of standing water and frost. Remove dust, laitance, grease, curing compounds, and any other contaminants. Frost on the surface is a non-starter.

Mix it right. Two-part epoxies need real mixing, not a quick stir. Mix thoroughly for a minimum of 3 minutes with a low-speed (400–600 rpm) drill fitted with a mixing paddle until uniform color is achieved. Scrape down the sides and ensure there are no streaks of unmixed epoxy before applying.

Respect the pot life. Mixed epoxy is on a clock. DURAL 617NS runs a pot life of 60–90 minutes. Do not mix more material than can be placed in 30 minutes. Mix only what you can place in the window — the rest is wasted in the bucket.

Watch the temperature. Most of these products want roughly 40 to 100 °F ambient air temperature to apply. DURAL 617NS lists an application range of +4°C to +35°C. For shoulder-season work in a Montana spring or fall, that’s the number to confirm before you open the kit. Some epoxies are sold in cold-weather temperature grades — Sikadur-31 SBA, for instance, comes in three temperature grades, with a separate cold-weather data sheet for the 20°–45°F range. Match the grade to the day.

Tools. Cartridges run through a caulking gun. Bulk systems get troweled or pumped.

Frequently Asked Questions

What’s the difference between a structural and non-structural adhesive? Strength. Structural adhesives give at least 5 to 8 MPa tensile shear strength and are meant for load-bearing joints like concrete-to-concrete, masonry, and metal bonding. Non-structural adhesives bond decorative materials — floor and wall coverings, panels, trim, some interior doors — that don’t need very high strength.

Should I use epoxy or polyurethane for a joint that moves? Polyurethane. Unlike epoxy, which tends to be rigid once cured, polyurethane adhesives are more flexible and can absorb shock and vibration. Epoxy’s rigid strength is built for static structural loads, not joints that expand and contract.

Can I bond concrete in damp conditions? Yes, if the product is rated for it. DURAL 617NS is moisture insensitive during and after curing. The universal rule across products: the surface may be dry or damp, but free of standing water and frost. Standing water and frost both kill the bond.

Is silicone a structural adhesive? No. Silicone is for sealing joints, not load-bearing bonding. If the joint has to carry weight, reach for epoxy, structural polyurethane, or a hybrid.

How long do I have to work with mixed two-part epoxy? Depends on the product and temperature, but it’s limited. DURAL 617NS gives 60 to 90 minutes of pot life. Mix only what you can place in that window — once it starts to set in the bucket, it’s done.

Does temperature affect application? Significantly. Most products apply in roughly the +4°C to +35°C (40–95°F) range. Some epoxies offer dedicated cold-weather grades for shoulder-season work — confirm the temperature range on the data sheet before applying in a Montana spring or fall.