There are often situations where connecting or joining concrete surfaces is necessary to create larger structures or make repairs. This requires proper concrete-to-concrete bonding utilizing the right adhesives and techniques.
Why Bond Concrete to Concrete?
Bonding concrete to existing concrete opens up many possibilities that cannot be achieved using concrete alone. Here are some of the main reasons you may need to glue concrete surfaces together:
Repairs
One of the most common reasons to bond concrete is for repairs. Concrete inevitably cracks, crumbles, and deteriorates over time due to factors like weathering, physical impacts, and ground movement. Adhesives allow you to patch small cracks and faults, or overlay larger sections, restoring the integrity and appearance of the concrete.
Extensions
It is often necessary to add new concrete sections onto existing foundations, slabs, or structures. Adhesives provide a seamless way to join the old and new concrete, creating a continuous surface. This might include adding a new concrete patio, path, or driveway extension.
Structural Enhancements
Adhesives can create extremely strong bonds between concrete surfaces. This allows you to improve the structural performance of concrete elements. For example, bonding rebar or post-tensioning cables into existing slabs can strengthen and reinforce them.
Aesthetic Improvements
Overlaying decorative finishes like pavers, tiles, or stone on top of existing concrete can provide an attractive facelift. Concrete adhesives allow these finishes to be bonded seamlessly to the surface.
Connecting Components
Bonding is useful for connecting pre-cast concrete components like bricks, blocks, or retaining wall sections. The adhesive joints replace traditional mortar for a quicker and easier installation.
Versatility
Adhesives allow concrete to be joined to itself as well as many other materials. This tremendously expands the design and construction possibilities with concrete.
So whether you need to make repairs, enhance functionality, or improve aesthetics, gluing concrete opens up many useful applications not possible otherwise. The key is selecting the right adhesive and application method for the specific job.
Types of Adhesives for Bonding Concrete
Choosing an appropriate adhesive is one of the most important factors in achieving effective, long-lasting bonds between concrete surfaces. There are a number of adhesive options, each with their own advantages, limitations, and ideal applications.
Epoxy
Epoxy adhesives are widely considered the top choice for bonding concrete. They are composed of two parts – a resin and a hardener – that must be mixed immediately before use. Here are the benefits epoxy offers:
- Extremely strong and durable bonds
- Resistant to water, chemicals, and temperature extremes
- Allows heavy loads and impact forces
- Versatile for many applications
- Available in fast-curing formulations
Epoxy is ideal for demanding situations like structural repairs that require high strength. It can be used for overlays, injection into cracks, and bonding rebar/posts. The downside is epoxy can lack flexibility. It also requires careful surface prep and proper mixing technique.
Polyurethane
Polyurethane concrete adhesives offer many similar benefits to epoxy but with greater flexibility. This makes them well-suited for bonding dissimilar materials or surfaces prone to movement and vibration. Polyurethane adhesives provide excellent adhesion and are easy to dispense using caulking guns. Popular brands like Loctite PL Premium Max work well for concrete bonding.
Acrylics & Latex
Acrylic or latex-based adhesives are designed primarily for bonding concrete overlays. They are easy to apply, have good flexibility, and are low odor. However, acrylics do not offer the same high strength and water resistance as epoxies and polyurethanes. They are best suited to decorative overlays rather than structural repairs.
Cementitious Grouts
Cement-based grouts are used for repairing cracks, voids, and faults in concrete. They are inexpensive, but slower curing and less adhesive than other options. Cementitious grouts are often used in conjunction with epoxy adhesives. The epoxy bonds and seals the crack, while the cement patch provides bulk and support.
Construction Adhesives
All-purpose heavy duty construction adhesives can also be used as a simple option for concrete bonding. These are one-part adhesives that typically use a polyurethane or acrylic base. While convenient, they may not offer the same performance as dedicated two-part epoxy or polyurethane adhesives.
PVA Glue
Regular PVA wood glue is sometimes used for minor concrete repairs around the home. It offers a decent bond strength and is easy to apply. However, PVA glue is not suitable for structural repairs or exposed areas due to poor water and temperature resistance. Epoxy or polyurethane adhesives are a better choice.
Surface Preparation
Achieving proper adhesion relies heavily on correct surface preparation. The goal is to create a clean, textured surface that enables the adhesive to mechanically grip the concrete. Here are the key steps:
Cleaning
All loose particles, dust, oil, grease, paint and other contaminants must be removed. Use a pressure washer or wire brush to clean concrete surfaces. Solvents or degreasers can remove stubborn oil stains. Allow the concrete to fully dry after cleaning.
Profiling
Creating an irregular, textured surface profile improves mechanical adhesion. This can be accomplished by acid etching, grinding, sandblasting or using a scabbler. Etching with muriatic acid is a common and economical option.
Repairs
Any significant cracks, spalls or deteriorated areas should be repaired prior to bonding. Use cementitious or epoxy patching compounds to fill voids and rebuild surface integrity.
Priming
Some adhesives work best with a primer coat designed to further prepare the surface and create a tacky layer. Primers promote maximum adhesion.
Take the time to properly clean and profile the concrete before attempting to bond it. Rushed surface prep leads to poor adhesive performance or even complete debonding. Testing surface tensile strength is also recommended.
Application and Curing
With the surfaces prepped, the next key factor is proper adhesive application and curing:
- Carefully follow the adhesive manufacturer’s instructions for mixing, pot life, application, clamping, and curing.
- Dispense and spread the adhesive evenly across the surface using the recommended technique – trowel, roller, grout gun etc.
- Maintain the required thickness. Spreading too thin compromises strength. Too thick slows cure time.
- Ensure sufficient adhesive contact by clamping or weighting surfaces together as needed.
- Allow adhesive to fully cure as specified prior to stressing or exposing bonded surfaces.
- Monitor temperature and humidity. Heat accelerates curing while low temps or humidity prolongs it.
- Avoid moving or disturbing joints until adhesive has hardened. Premature loading or movement can ruin the bond.
Proper curing is critical so the adhesive can fully harden and achieve its designed strength. Inadequate curing leads to soft, weak bonds prone to failure. Be patient and allow the recommended cure time before exposing bonded concrete to loads or harsh conditions.
Bonding Fresh Concrete to Existing Concrete
Pouring new concrete against existing concrete surfaces is a common application for concrete bonding. Here are some tips:
- The existing surface must be clean and roughened via etching or abrasion.
- Saturate the surface with water before pouring fresh concrete. This prevents premature drying.
- Right before the pour, brush a cement slurry coating onto the old concrete. This helps integration.
- Tie in the new pour with reinforcing rods epoxied into pre-drilled holes. Mechanical ties boost strength.
- Pour the fresh concrete while the slurry coat is still wet. Work it against the surface.
- After curing, seal the joint with an epoxy or polyurethane adhesive for maximum integrity.
Properly joining existing and new concrete requires paying close attention to surface, preparation, mechanical ties, and finishing to get optimal strength.
Repairing Cracks and Faults
Concrete cracks are inevitable but properly repairing them restores structural integrity and appearance. Here are proven methods:
Minor Cracks
- Etch crack faces and surrounding area then apply epoxy adhesive.
- Pressure inject epoxy for deep penetration then trowel smooth.
- Alternately, fill cracks with polyurethane or acrylic caulk.
Major Cracks
- Use a diamond blade saw to open large cracks into a v-shape.
- Clean and etch inside the crack then vacuum debris.
- Fill the crack with epoxy via ported injection tubes.
- Inject epoxy in stages, allowing each layer to partially cure.
- Finish by over-coating the epoxy with a bonding agent and cementitious patching compound.
Moving Cracks
- Dynamic cracks require flexible sealant like polyurethane.
- Injection ports can be installed to allow re-injecting if movement occurs.
- Alternatively, route a 1⁄2” deep groove over crack then fill with sealant.
Leaks
- Use hydraulic cement or rapid-setting mortar plugs to stop water leaks.
- Inject hydrophilic polyurethane foam designed to seal wet cracks.
- Epoxy injection can also work but requires dry conditions.
Repair success depends on correctly diagnosing the crack type, stabilizing movement, and meticulous adhesive application. Consult concrete repair specialists for large projects.
Overlaying Concrete
Applying a fresh layer of concrete or other finish over existing concrete is an excellent restoration technique known as overlay. Reasons include:
- Improving wear/impact resistance
- Correcting surface imperfections
- Achieving a decorative appearance
- Changing the height or slope
Overlays require thorough surface preparation and proper adhesive selection:
- For thin skim coats, use polymer-modified cementitious toppers.
- For thicker resurfacing, latex or acrylic bonding adhesives work well.
- Epoxy adhesives allow the greatest overlay thickness buildup.
- Always apply a primer coat suited for the overlay adhesive used.
- Smooth and level overlays carefully to prevent delamination.
Overlays can transform old, damaged concrete into a fresh, attractive surface. Pay close attention to prep work, adhesive selection, and proper curing.
Safety Considerations
While invaluable, concrete adhesives also require safe handling:
- Wear gloves, eye protection and respiratory masks when appropriate. Adhesives can irritate skin and eyes.
- Work in well-ventilated areas when using solvent-based adhesives.
- Prevent flame or sparks near flammable epoxy and polyurethane products.
- Follow all manufacturer safety directions for proper use, cleanup and storage.
- Dispose of used containers and waste adhesives correctly.
Bonding concrete provides immense utility but also involves powerful chemicals. Take the necessary safety precautions when working with adhesives.
Conclusion
Gluing concrete to itself or other surfaces opens up many beneficial applications in construction, repair, and restoration work. With proper adhesive selection, surface preparation, application, and curing, concrete can be bonded together to create seamless connections. Epoxy adhesives in particular make joining concrete possible in even heavy load, high strength situations. Paying attention to details and process will ensure you achieve bonds that live up to the design requirements.