Concrete Bonding: Methods, Agents, and Applications

Will Concrete Bond to Concrete?

Concrete is a building material with high compressive strength. But it does not have a bonding ability. Concrete will deteriorate over time.  When it does, we either have to repair or replace it. We need a bonding agent if we want to bond dry concrete to wet concrete.

We use Mechanical reinforcement such as rebar or wire mesh to attach concrete structures to each other, but we need a chemical bonding agent to make concrete bonds.

An existing concrete slab Apply a chemical bonding agent to the concrete slab with a roller or brush.  Once the concrete dries, new wet concrete poured onto existing concrete will adhere. When we pour fresh wet concrete over dry concrete, it’ll dry as an independent layer.

Pouring 3 inches of new concrete on a 5-inch slab doesn’t create an 8-inch slab. What we get is two slabs sitting on each other. After using a bonding agent, the two layers stick together. They’ll still be two separate layers but stuck together tightly.

How Concrete Adhesion Works?

Concrete bonding agents are natural materials that join old and new concrete surfaces. Concrete is a building material made from cement, rock, sand, water, and admixtures. Dried concrete doesn’t have any natural bonding agents. 

A bonding agent helps the different concrete layers behave like a single layer, increasing the structure’s strength.  The bonding agent is applied over the former surface of the concrete so the new layer of concrete successfully adheres to the old coating.

Why Do You Need to Use a Concrete Bonding Agent?

The mixture of cement and concrete doesn’t contain any natural bonding agents. When a concrete floor surface is damaged, there is a choice to either demolish the floor or resurface the existing concrete.

If the foundation is still structurally sound, Removing the entire floor and re-pouring is costly and a waste of time and money.  A further solution is to apply new concrete on the surface of an old surface.

When fresh concrete is added to the top of a current layer of concrete, the two won’t join together due to inadequate bonding. Once the top layer is set, it simply sits on the top of the layer as a top layer. Concrete is poured before it gets hard. 

Prepare the Surface for Concrete Bonding

It is mandatory to have a clean surface. Surface preparation for the concrete repair work is important for developing a strong bond with the new concrete.

The concrete surface consists of dust, grease, oil, sand, or grit blasting efflorescence; the bonding agent will not work properly.  Ensuring that the bonding agent works properly on the concrete surfaces is important. In this article, we discuss the different steps for preparing the surface. 

Step 1: Clean the Surface

Firstly it is essential to have a clean surface. The bonding agent will not work correctly if the existing concrete surface consists of dust, oil, grease, or efflorescence. This step ensures the bonding agent works well on the concrete surface.

Step 2: Prepare the Mixture

The container of bonding agent is shaken well before use. The chemical is poured into a separate bowl and diluted with water according to consistency.

Now we can use this mixture as a primer. The concrete chemical might not work properly, so following the instructions mentioned in the container is essential. 

Step 3: Placing the Concrete Bonding Agent

We need to follow standard instructions to produce and place the concrete. After mixing of bonding agent with concrete, we immediately applied it to the surface.

The primary coating dries off and loses its adhesion after some time, so spread the mixture when it is tacky and not dry completely. 

Choose a Bonding Method:-

There are various types of concrete bonding agents used in construction:-  

1. Latex Emulsions

Latex emulsions are commonly used as oil-in-water type emulsions in cementitious compositions.  These emulsions contain more than 50% water in some compositions. Some bonding agents have more resistance to water than other bonding agents.

Latex emulsions contain more than 50% water in some compositions. The constitution of latex emulsions is stable in water & cement systems.  There are three ways to change latex emulsions into helpful bonding agents.

2. Acrylic Latex

This agent is mainly used to bond fresh concrete with a surface of old concrete. Acrylic Latex Bonding Agents are milky white, combining polymers and co-polym45% solid content. Apply it on the surface with either a brush or a roller. 

3. Styrene Butadiene

Styrene Butadiene is a type of latex emulsion agent that is a co-polymers, and it is compatible with cement. It may solidify if SBR latex is at high temperatures for an extended period. It is used for waterproofing roof slabs, basements, hollow slabs, water tanks, sunshades, etc.

It can be used as a plaster bond within 45-60 minutes. It is used for the treatment of leaching and saltpeter action. SBR latex is also milky white, like Acrylic latex.

4. Polyvinyl Acetate Latex(PVA)

Polyvinyl Acetate latex (PVA) is used for repair applications in the construction industry.

There are two types of Polyvinyl Acetate latex.

1. Non-Re-Emulsifiable PVA
2. Emulsifiable

4.1. Non-Re-Emulsifiable PVA

Because of its compatibility with cement, it is used as a bonding agent. PVA latex is utilized as a binder for cementitious water-based paints & waterproofing coatings.  When applied, this bonding agent builds a thin layer highly resistant to water and ultraviolet rays.

4.2. Emulsifiable PVA:

When an emulsifiable PVA is applied on the surface, it produces a film that is getting softened and rewetted with water if necessary.  PVA latex is used as a bonding agent for plaster. Polyvinyl Acetate Latex (PVA) utilization is limited to areas with no possibility of moisture infiltration to the bond line.

5. Epoxy resin:-

Epoxy resin is the most versatile of all concrete bonding agents. It is ideal for lightweight parts & high performance.  Because of their high compressive strength, chemical resistance, strong adhesion, and other unique properties, it is widely used in construction.

Epoxies bond well with almost every material when the surface is properly prepared. Epoxy Resin is classified according to type, class, and grade. 

American Society for Testing and Materials classified the epoxy-resin bonding systems classification based on specific aspects of class type, grade, and color.

Based of Type, It Has Seven Types:-

1. Type 1:- This epoxy resin is mainly used to bond fresh concrete with old hardened concrete.
2. Type 2:- Usually this type is commonly used to bond freshly mixed concrete with cured concrete.
3. Type 3:- It is used as a binder in epoxy mortars and concrete. It bonds with the skid-resistant materials to the cured concrete.
4. Type 4:- Usually used in load-bearing applications. This type of Epoxy resin is used as a binder for epoxy mortars and concrete.
5. Type 5:- This bonds hardened concrete together with freshly mixed concrete.
6. Type 6:- It is used for bonding and sealing segmental precast elements with internal tendons.
7. Type 7:- When temporary post-tensioning is not applied as in span-by-span erection, it is for segmental precast elements used as a non-stress carrying sealer.

Based on Grade:- 

Based on grade classification is as follows: 

1. Grade I: Mainly consists of materials with low viscosity suitable for injection into the cracks and where the flow is required.
2. Grade II:  It is used for general concrete bonding purposes. This type consists of materials with medium viscosity.
3. Grade III: The epoxy resin comprises materials with non-sagging consistency.

Based on Class:- 

It is based on the test temperatures. The classification is as follows:-

1. Class 1:- In this class, temperatures should be below 5°Celsius.
2. Class 2:- In this class, the temperature range should be 5°Celsius to 15°Celsius.
3. Class 3:- In this class, the temperature should be above 15°Celsius.

Liquid Bonding Agents

Polyvinyl Acetate(PVA) offers excellent water resistance, aging characteristics, and ultraviolet stability. For the repair works in concrete, this agent is mainly used.

PVA offers excellent ultraviolet stability, aging characteristics, and water resistance. Liquid bonding agents are the best way to bond dry concrete to wet concrete. 

The Best Concrete Bonding Agent

Concrete is one of the important building materials. The best concrete bonding agents must be easy to apply and use. It provides great adhesion and enhances the concrete and bond strength. 

Different Types of Concrete Bonding Agents Used in Construction:- 

1. Quikrete 1 Gal. Concrete Bonding Adhesive.
2. Quikrete 1 Qt. Acrylic Fortifier.
3. SikaLatex 1 Gal.
4. Loctite PL Premium Polyurethane Construction Adhesive.
5. Liquid Nails – LN-905 Landscape Block Adhesive.

What Will Concrete Stick To?

Concrete usually sticks with Wood, plastics, metal, vinyl, Cloth, and other porous surfaces. Concrete also sticks to porous surfaces, Plastic, and some rough metal. These Materials Will Stick To Concrete:

1. Wood: Generally, concrete will stick to Wood poorly. However, you can do a few things to help improve the bond between the two materials. The roughness and more porous Wood will help to stick with concrete. You can also use a bonding agent or primer before applying the concrete.
2. Plastic: concrete sticks very well with plastics. Use a release agent if you don’t want concrete sticking to your plastic tools and buckets.
3. Cloth: splatter of concrete will stick to cloth and tarps. 
4. Porous Surfaces: If a surface is porous, concrete can stick easily. It works with the pores and forms a bond.

What Will Concrete Not Stick To?

Concrete doesn’t stick with molds, glue, paint, smooth metal, oil, mortar, other concrete, or most masonry products. Concrete doesn’t bond with concrete if you want to bond with concrete, you need to use a bonding agent first. Bricks, stones, and mortar are not great at bonding.

Downsides of Bonding Concrete to Concrete

Although bonding concrete to concrete has some big benefits, there are downsides too.  One of the major disadvantages the weight of concrete is high compared to its strength. When we pour concrete, it does not gain strength we have to wait till it gains strength.

Adding new concrete over existing concrete increases the height of the slab. Usually new layer is thinner than the bottom so it cracks easier. 

Will Cement Stick to Concrete?

No, cement will not stick to concrete. Concrete mix within the cement doesn’t contain any natural bonding agents.  So when fresh concrete is added on the top of an existing concrete, it doesn’t join together. 

FAQ

What is a concrete bonding agent, and why is it necessary?

A concrete bonding agent is a material applied to surfaces to enhance adhesion between old and new concrete layers. It is necessary because fresh concrete does not naturally bond well with cured concrete surfaces, requiring a bonding agent to create a strong connection.

How does a concrete bonding agent work?

Concrete bonding agents contain ingredients that promote adhesion by penetrating pores and creating a chemical bond between the new and existing concrete layers. This helps the concrete layers behave as a single, integrated unit.

What are the different types of concrete bonding agents?

There are several types, including latex emulsions (such as acrylic latex and styrene butadiene), polyvinyl acetate (PVA), and epoxy resin. Each type has specific properties suited for different applications, from general concrete bonding to specialized uses like waterproofing and high-performance bonding.

How do you apply a concrete bonding agent?

Application methods typically involve cleaning the surface thoroughly, applying the bonding agent with a brush or roller, and ensuring the surface remains tacky for optimal adhesion of the new concrete layer.

What are the benefits of using a concrete bonding agent?

Using a bonding agent enhances structural integrity, prolongs the life of concrete surfaces by reducing the need for complete replacement, and allows for efficient repair and resurfacing of damaged concrete without compromising strength.

Can concrete bond directly to other materials?

Concrete adheres well to porous materials like wood, plastic, and cloth, but not to smooth surfaces like metal, painted surfaces, or other non-porous materials. Special techniques or bonding agents may be required for bonding concrete to non-porous surfaces.

What are the downsides of bonding concrete to concrete?

While effective, bonding concrete to concrete can increase the overall weight and height of structures, potentially leading to issues such as increased cracking and longer curing times. Proper preparation and application are essential to mitigate these challenges.

How can I ensure the best results when using a concrete bonding agent?

To achieve optimal results, ensure the concrete surfaces are clean, free of contaminants, and properly prepared according to manufacturer guidelines. Follow recommended application techniques and allow sufficient curing time for the bonding agent and concrete layers.

Can cement be used as a bonding agent for concrete?

No, cement itself does not contain bonding agents that promote adhesion between concrete layers. A separate concrete bonding agent is necessary to ensure a strong bond between old and new concrete surfaces.

When should I consider using a concrete bonding agent?

Use a concrete bonding agent when repairing or resurfacing existing concrete surfaces, adding new layers to old concrete, or ensuring a strong bond between fresh and cured concrete in construction and renovation projects.