When it comes to concrete projects, you can’t simply pour new concrete over an old slab and expect it to bond properly. Without the right preparation, the two layers remain separate, leading to major issues down the road. So, what do you put between old concrete and new concrete to make sure it all holds together? The answer: a concrete bonding agent.
In this article, we’ll break down why bonding is crucial, how a concrete bonding agent guide can help you choose the right materials, and how proper preparation can even set the stage for beautiful concrete floor polishing once the project is complete.
Why Proper Bonding Matters
Concrete may seem like it should easily stick to itself, but the truth is, it doesn’t naturally bond when you pour new material over old. If you skip the bonding step, you’re risking serious problems later, including cracks, delamination, surface unevenness, and general structural instability.
According to the American Concrete Institute (ACI), bond strength between concrete layers can be up to 80% lower when no bonding agent is used. That’s a massive risk to take, especially for floors in high-traffic or critical-use spaces.
Ensuring the old and new concrete layers fuse properly is not just a recommendation — it’s essential for a long-lasting, quality finish.
What Is a Concrete Bonding Agent?
A concrete bonding agent is a specially designed material that promotes adhesion between new and existing concrete surfaces. Think of it as the critical middleman that forms a strong, lasting bond.
There are several different types of bonding agents available. Epoxy-based products are known for their strength and are often used in heavy-duty applications like industrial floors. Latex-based bonding agents are a bit more flexible and are popular for residential or decorative overlays. Acrylic bonding agents offer great resistance to moisture and UV exposure, making them a smart choice for outdoor projects.
Choosing the right bonding agent depends on factors like your environment, the condition of the existing concrete, and the kind of finish you plan to apply afterward, such as concrete floor polishing.
A Practical Concrete Bonding Agent Guide
When asking, what do you put between old concrete and new concrete, it’s important to think about the process from start to finish.
First, evaluate the condition of your old concrete. If it’s dirty, greasy, cracked, or coated with sealants or paint, you’ll need to properly clean and prep the surface.
Pressure washing is usually a good starting point, but in some cases, mechanical profiling techniques like grinding, scarifying, or shot blasting may be necessary to achieve a roughened surface that encourages strong bonding.
Once the slab is clean and prepped, you’ll need to select the right bonding agent. For structural repairs or heavy-use floors, an epoxy bonding agent is often the best choice because of its high strength. Latex bonding agents work well for lighter applications like decorative overlays, while acrylic options are versatile enough for indoor and outdoor use.
Always check the product’s specifications to ensure it matches your needs, especially if you plan to move on to concrete floor polishing later.
When it’s time to apply the bonding agent, most products can be brushed, rolled, or sprayed onto the surface. Some require a “wet-on-wet” approach where you apply new concrete while the bonding agent is still tacky, while others might call for letting it fully dry first. Reading and following the manufacturer’s instructions carefully is vital to avoid adhesion failures.
Understanding the Difference: Bonding Agents vs. Bond Breakers
It’s important not to confuse bonding agents with bond breakers. While bonding agents are used to make new concrete stick to old concrete, bond breakers are designed to do the opposite — they prevent adhesion. Bond breakers are commonly used in tilt-up construction or when pouring concrete forms that need to be removed later.
If your goal is to seamlessly unite old and new concrete into a single, durable surface, you’ll need a bonding agent, not a bond breaker.
The Role of Concrete Floor Polishing After Bonding
If you plan to upgrade your space further, you might be considering concrete floor polishing once your bonding and overlay work is complete. Properly bonded and resurfaced concrete provides the perfect foundation for polishing, giving you a floor that is not only smooth and beautiful but also durable and easy to maintain.
Polished concrete floors are highly reflective, meaning they can boost natural and artificial lighting in a space by as much as 30%, according to studies. This makes polished concrete an energy-efficient and visually striking option for homes, offices, and retail environments.
Additionally, by creating a properly bonded surface first, you minimize the risk of cracks, lift spots, or surface imperfections disrupting your polished finish later. Bonding well from the beginning ensures a more uniform, professional result that lasts for years.
Best Practices for Successful Concrete Bonding
If you want to avoid future problems, surface preparation is everything. The old concrete must be clean, roughened, and free of any contaminants that could interfere with adhesion. It’s also important to consider environmental conditions during your project.
Ideally, work in moderate temperatures between 50°F and 85°F, and be cautious of working on extremely dry slabs, which can pull moisture out of the new concrete too quickly.
Using a moisture-wetted (but not saturated) surface often leads to better bonding results. And if you’re using specialized overlays or toppings, make sure your concrete mix is compatible with the bonding agent you’ve selected.
Taking your time during prep and bonding ensures a much stronger, longer-lasting final product, whether you’re simply resurfacing a slab or planning for a polished showpiece.
Concrete’s Surprising Strength
You might not realize it, but concrete is one of the strongest construction materials in existence. Properly placed and cured, concrete can reach compressive strengths of 5,000 psi or more, and specialized mixes can even exceed 20,000 psi.
This strength, combined with proper bonding techniques and finishing processes like concrete floor polishing, can create incredibly resilient, beautiful floors that stand the test of time.
Start Strong with the Right Bond
So, what do you put between old concrete and new concrete? A high-quality concrete bonding agent — and a little bit of know-how. With the right preparation, product choice, and attention to detail, you can create a seamless surface that looks great, holds up to wear, and serves as the perfect canvas for modern finishes like polished concrete.
Investing the effort into proper bonding today means fewer repairs, lower maintenance costs, and a more polished final result tomorrow.
Ready to Ensure a Seamless Concrete Bond?
Contact Custom Concrete Prep & Polish today to get expert help with surface preparation, bonding, resurfacing, and beautiful concrete floor polishing. Our team is ready to transform your old concrete into something strong, stylish, and built to last.
