What Is the Best Concrete Bonding Agent?

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When your concrete floor is damaged, the less costly solution would be to add a fresh concrete on top of the damaged surface or use concrete to fill gaps created by the damage. However, the two layers will not form a strong, serviceable floor as cement within the concrete mix does not contain any bonding adhesive; thus, the need for a bonding agent. But what is the best one to use?

The best concrete bonding agent should be easy to use and apply, provide excellent adhesion, reduce the permeability of concrete, and enhance the concrete’s tensile and bond strength. Furthermore, the bonding agent should provide excellent workability and resistance against frost and cracking.

The rest of this article is an in-depth guide to help provide answers to the topic question. Read on to get the information you need on the best concrete bonding agent to use to achieve your desired results.

Latex Emulsions

In cementitious compositions, latex emulsions are usually used as the oil in water type emulsions. Latex emulsions are categorized into three, with some compositions containing more than 50% water. Some also have greater resistance to water than others.

The composition of latex emulsions is stable in water and cement systems though not all emulsions are compatible with cement. Therefore, to select the appropriate latex emulsion for your project, you need to understand its chemistry.

Using latex without cement content in the mix will result in a failure plane as there is no film formation at the bond interface. However, there are three ways to modify latex emulsions into useful bonding agents:

  1. Prepare a neat cement slurry with latex forming part of the mixing water.
  2. Use one-part water to one-part latex diluted material.
  3. Use re-emulsifiable latex as it can be rewetted and softened when it gets in contact with water.

Acrylic Latex

Acrylic latex is primarily used in the bonding of fresh concrete to the old one. This milky white latex emulsion consists of 45% solid content, Apply it with either a brush, broom, spray, roller, or a trowel.

Styrene Butadiene (SBR) Latex

SBR Latex is a type of latex emulsions that is a co-polymer and compatible with cementitious compounds. This bonding agent is milky white in appearance and consists of 55% solid content. SBR Latex can be used for the following purposes:

  • Bonding fresh concrete to old concrete
  • Bonding fresh concrete to thin layer toppings
  • As a plaster bond within 45 minutes to an hour

If subjected to severe mechanical action, high or freezing temperatures for extended periods, SBR Latex may coagulate.

Polyvinyl Acetate (PVA) Latex

There are two types of PVA Latex:

  • Non-Re-Emulsifiable PVA – Non-re-emulsifiable PVA Latex is commonly used as a bonding agent because of its compatibility with cement. This latex can also be used as a binder for cementitious water-based paints and waterproofing coatings. When applied, this bonding agent forms a thin layer that is highly resistant to water, aging, and ultraviolet rays.
  • Emulsifiable PVA – When an emulsifiable PVA is applied, it produces a film that can be softened and rewetted with water if necessary. The film can be applied long before the application of a water-based overlay. This latex is used as a bonding agent for plaster. Additionally, emulsifiable PVA is used to bond finisher base-coat gypsum to interior surfaces of cured cast-in-place concrete.

Polyvinyl Acetate Latex use is limited to areas where there is no possibility of infiltration of moisture to the bond line.

Epoxy Resin

Epoxy Resin is known for being the most versatile of all concrete bonding agents. This bonding agent is ideal for high performance and lightweight parts. Characterized as being strong but brittle, Epoxy Resin can be formulated to become more flexible without losing its tensile strength.

Epoxy Resin is a bonding agent widely used in the construction field because of its high compressive strength, chemical resistance, and strong adhesion. Epoxy Resin has an excellent bonding capability, wets out quickly, and can be used for bonding to a variety of materials as long as the surface is well-prepared.

Some of the properties that give Resin epoxies excellent adhesion characteristics include:

  • Cured epoxy resins give tensile and comprehensive strengths higher than concrete
  • Epoxy Resin compounds in liquid forms do not contain any volatile solvent. Liquid resin turns into 100% solids after curing
  • Epoxy Resin can adhere to almost all construction materials
  • During the curing period, Epoxy Resins, do not produce any by-products
  • Shrinkage during or after curing is minimal
  • Once cured, epoxies have dimensional stability

Epoxy Resin is used:

  • For fresh bonding concrete to old concrete
  • For bonding of concrete to steel
  • Can be formulated to cure at room temperature and elevated temperatures, under wet or dry conditions
  • For preparing concrete for repairing spalls and other defects such as cracks in concrete

Epoxy Resins are available in different consistencies, from highly filled pastes to water-like liquids and may contain fillers.Epoxy Resins also classified according to type, grade, and class.

Type

Under this classification, the Resin Epoxy bonding system is classified according to physical requirements.

  • Type I: Used to bond fresh concrete together with the old hardened concrete.
  • Type II: Usually used to bond the freshly mixed concrete together with the cured concrete.
  • Type III: Commonly used for the bonding of skid-resistant materials to the cured concrete.
  • Type IV: Usually used in load-bearing applications. This bonds the already hardened concrete into hardened concrete.
  • Type V: Used load-bearing applications. This bonds freshly mixed concrete together with the hardened concrete.
  • Type VI: Used to bond and seal segmental precast elements with internal tendons.
  • Type VII: Used as a non-stress carrying sealer for segmental precast elements when temporary post-tensioning is not applied.

Grade

This classification of epoxy resins is based on flow viscosity.

  • Grade I: Consists of materials with low viscosity. Grade 1is suitable for injection into the cracks or areas where the flow is needed.
  • Grade II: Consists of materials with medium viscosity. It can be used for general concrete bonding purposes.
  • Grade III: Comprises materials with non-sagging consistency.

Class

This classification, based on the test temperatures, the gel times are determined.

  • Class A: The epoxy systems in this class should be below temperatures of 5°Celsius.
  • Class B: The epoxy systems should be in the temperature range of 5°Celsius to 15°Celsius.
  • Class C: The epoxy systems should be above 15°Celsius temperature range.

Conclusion

Damage on a concrete surface leaves you with two options: to demolish or to re-surface. Removing the old concrete and pouring a fresh one is costly, time-consuming, and wasteful, especially if the concrete was still structurally sound. The better solution would be to resurface the old concrete with a layer of fresh concrete.However, the new layer of concrete will settle on top of the old surface as a separate layer. You should first spread the concrete bonding agent on the damaged surface. The new concrete layer will then adhere appropriately to the old layer, forming a single unit.

Consider the following when applying the concrete bonding agent as they will affect the bonding between the damaged and the new concrete:

  • The cleanliness of the damaged surface. Bonding agents are more effective on clean, dry, and sound surfaces.
  • Condition, strength, and soundness of the old surface.

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