Choosing an Anchor: Mechanical or Chemical?

Anchor selection and installation quality based on concrete condition, edge distance and load type.

In every application fastening into concrete, the first question is: mechanical or chemical anchor? The choice depends on concrete condition, load type, edge distance and installation conditions.

How does a mechanical anchor work?

In mechanical anchors (wedge, sleeve, hammer-set), a part that expands in the hole transfers load to the concrete through friction and mechanical interlock. Installation is fast, it can take load immediately, and it is economical. However, expansion creates internal stress in concrete; performance is limited near edges and in cracked concrete.

How does a chemical anchor work?

In a chemical anchor, the threaded stud bonds to the concrete through resin in the hole; load is transferred by bond stress. As there is no expansion pressure, it suits near-edge installation, cracked concrete and high loads. Cure time depends on temperature (~60 minutes at 20 °C, several hours at 5 °C).

Selection table

Condition	Recommendation
Uncracked concrete, medium load, fast installation	Mechanical anchor
Cracked concrete, seismic load	Chemical anchor (ETA approved)
Near-edge installation (< 5 × embedment depth)	Chemical anchor
Permanently wet / outdoor	Chemical anchor, A4 stainless
Light load, racking and railing	Mechanical anchor

Installation quality determines capacity

Anchor capacity is given in tables under test conditions; to achieve it on site, pay attention to the following:

Hole diameter and depth: The drill bit must be the correct diameter and not worn.
Hole cleaning: For chemical anchors 3 brushings + 3 blow-outs; dust can reduce capacity by up to 50%.
Edge and axis distances: Minimum values in the table must be respected.
Tightening torque: For mechanical anchors, follow the manufacturer's torque; overtightening causes failure.

Common mistakes

Using the first resin out of the mixer nozzle (the part with uneven color) in chemical anchors
Hammering a mechanical anchor into a hole shorter than the embedment depth
Applying load at low temperature without waiting for the cure time
Placing the anchor without cleaning dust from the bottom of the hole

Which anchor should carry which approval?

For structural and safety-critical applications use ETA (European Technical Assessment) approved anchors; this approval also covers cracked concrete and seismic category performance. Kenet has ETA-optional anchors; we supply the documents with the lot certificate.

For a project-specific load calculation and anchor selection, contact our application engineers.