What Is a Chemical Anchor?
A chemical anchor is a post-installed connection system that uses a reactive adhesive — typically epoxy, vinyl ester, or a hybrid blend — to bond steel elements (threaded rods, rebar, bolts) into holes drilled in hardened concrete, masonry, or natural stone. The adhesive fills the annular gap between the steel element and the hole wall, creating a structural bond that transfers load through shear along the bonded surface.
Chemical anchors are the preferred solution when mechanical expansion anchors cannot meet the load, spacing, or edge distance requirements of the design.
Three Main Chemistries Compared
Pure Epoxy
Our standard epoxy anchors (XQ-ZJ-E585, XQ-ZJ-360) use a two-component epoxy resin with no styrene content.- Strengths: Highest ultimate bond strength, excellent gap-filling capability, no shrinkage during cure, no styrene odor
- Limitations: Longer cure time than other chemistries, temperature-sensitive curing, not suitable for damp holes without special formulation
- Best for: Maximum load applications in dry conditions at moderate temperatures
Vinyl Ester
Our vinyl ester anchors (XQ-ZJ-V390, XQ-ZJ-VF650) use a methacrylate-based resin with peroxide hardener.- Strengths: Fast cure (even in cold weather), approved for cracked concrete, wet-hole capable, good chemical resistance
- Limitations: Contains styrene (requires ventilation), slight shrinkage during cure
- Best for: Seismic applications, cracked concrete, cold weather installation, wet conditions
Hybrid (Epoxy + Vinyl Ester)
Our hybrid anchor mortar (XQ-ZJ-HM) combines benefits of both chemistries.- Strengths: Moderate cure time, styrene-free, good performance in damp conditions
- Limitations: Intermediate performance — not the best in any single metric, but good across all
- Best for: General-purpose applications where versatility matters
Selecting the Right Chemical Anchor
The selection process follows a decision tree based on project conditions:
1. Is the concrete cracked? If yes → Vinyl ester or hybrid formulation required. Pure epoxy products are typically only approved for uncracked concrete unless specifically tested and certified for cracked concrete performance. 2. What is the ambient temperature? Below 5°C → Use fast-set vinyl ester (XQ-ZJ-VF650) or cold-weather epoxy. Standard formulations may not cure reliably. 5-35°C → Any chemistry works; choose based on other factors. Above 35°C → Working time becomes very short. Use extended working time formulations. 3. Is the hole wet or dry? Wet or submerged → Vinyl ester or hybrid only. Standard epoxy will not bond reliably to wet surfaces. Dry → Any chemistry works. 4. Is seismic performance required? If yes → Vinyl ester with seismic qualification (check certification for your seismic performance category). 5. Is overhead installation required? If yes → Use thixotropic (non-sag) formulations that will not drip from overhead holes.Rebar Anchoring: The Most Common Application
Post-installed rebar connections account for the majority of chemical anchor usage in structural applications. Typical scenarios include connecting new structural elements to existing concrete, extending floor slabs, adding shear walls, and seismic retrofit work.
For rebar anchoring, embedment depth is critical. Most design codes require a minimum embedment of 10 times the bar diameter (10d) for tension connections and 6d for compression-only connections. Our technical team recommends verifying embedment requirements against the applicable design standard for your project.
A properly installed M20 rebar at 200mm embedment in C30 concrete using our epoxy anchor adhesive provides a characteristic bond strength that typically exceeds the yield capacity of the rebar itself — meaning the rebar will yield before the adhesive bond fails.
Quality Control and Testing
Every batch of our anchor adhesive undergoes internal testing for:
- Bond strength (pull-out test in C20 and C40 concrete)
- Gel time and cure time at reference temperature
- Rheology (flow characteristics for injection)
- Shelf stability