SlabCalc LogoSlabCalc Concrete Technical Division

Bonding Agent

A liquid compound applied to old concrete to improve adhesion of new concrete patches or overlays

A bonding agent is a liquid compound applied to old concrete to improve adhesion of new concrete patches, overlays, or toppings. Bonding agents create a chemical and mechanical bond between old and new concrete that would otherwise have poor adhesion due to the old surface being smooth, contaminated, or non-porous.

Why It Matters

New concrete bonds poorly to old concrete. The old surface is smooth, carbonated, and often contaminated with oils or sealers. Without treatment, patches simply delaminate and pop off—sometimes within days. Bonding agents bridge this gap, creating reliable adhesion that allows repairs to last.

For DIY repairs, bonding agents are the difference between patches that fail repeatedly and repairs that last years. They're inexpensive insurance—a few dollars spent on bonding agent prevents having to redo work. Application is simple: clean the surface, brush on bonding agent, apply repair material while bonding agent is still tacky.

Technical Details

Bonding agent types:

Latex/acrylic bonding agents:

  • Polymer emulsions that improve adhesion and flexibility
  • Most common type for general repairs
  • Apply and work while wet (milky appearance)
  • Typical cost: $15-30 per gallon

Epoxy bonding agents:

  • Two-part adhesives providing strongest bond
  • Used for structural repairs, high-stress areas
  • Must maintain wet contact time (typically 30-60 minutes)
  • Higher cost: $50-100 per gallon

Cement-based bonding agents:

  • Thick slurry of cement, sand, and water
  • Traditional method, still effective
  • Apply and work while wet/tacky
  • Lowest cost: materials on hand

Surface preparation is critical:

  1. Remove all loose, damaged concrete
  2. Clean thoroughly—remove oil, grease, sealers, curing compounds
  3. Roughen smooth surfaces by grinding or acid etching
  4. Pre-wet porous surfaces (but no standing water)
  5. Apply bonding agent per manufacturer instructions
  6. Place repair material while bonding agent is tacky

Bonding agents don't fix structural problems or fill large voids—they only improve adhesion. Proper surface prep matters more than bonding agent quality. A clean, rough surface with mediocre bonding agent outperforms a contaminated surface with premium bonding agent.

  • Repair - Process bonding agents facilitate
  • Adhesion - Bond strength bonding agents improve
  • Cold Joint - Joint problem bonding agents can help prevent

Learn More

← Browse all glossary terms