Chemical or mechanical anchor? How to choose by base material

7 min read

The question comes back on every building site: do you choose a mechanical anchor or a bonded system? The answer does not depend on preference, but on the base material and the load. Below you read how the two principles work, why cracked concrete makes the difference and which anchor belongs with which base material.

Two ways to transfer force

Mechanical

A mechanical anchor holds by clamping force or by form fit. When you tighten a through bolt, it pulls a cone into an expansion sleeve, which presses against the wall of the drill hole. An undercut anchor makes a widening in the drill hole and locks into it. You can load it straight away, and you can check the anchor by its installation torque.

Bonded

A bonded system fills the space between the anchor rod and the drill hole with mortar. The force goes through the bond into the concrete or the masonry. This works well with small edge distances, in hollow bricks and where you do not want to introduce expansion force. You do need curing time, and the installation is sensitive: temperature, moisture and a clean drill hole help decide what the connection can carry.

What cracked concrete means

Concrete cracks, mainly in tension zones on the underside of floors, beams and brackets. You usually cannot see these hairline cracks, but they take the clamping force out of an anchor that is not assessed for them.

The ETA of the anchor states for which concrete condition it is approved. For fixings where failure leads to damage, such as sprinkler pipes and load-bearing structures, you choose an anchor that is assessed for cracked concrete. You use an anchor for non-cracked concrete only when it is certain that the concrete is non-cracked and stays that way.

By base material

Solid concrete, non-cracked

For multiple fixing of non-structural systems, such as pipe clamps and cable trays on a concrete ceiling, the EA II hammerset anchor is the usual choice. The ETA applies to non-cracked concrete and the anchor is fire-tested up to R120.

Solid concrete, cracked

Here you need an anchor with an ETA for cracked concrete.

Hollow-core slab floor

Masonry and hollow bricks

In solid brick and sand-lime brick a mechanical anchor can work, provided the edge distances allow it. In hollow and perforated brick, expansion force is exactly the problem: the wall of the cavity breaks. There, a bonded system with a sleeve is the usual solution. In both cases, choose a system with an assessment for exactly that type of brick, and calculate with the values from that assessment. A proof load test on site gives the certainty that documentation cannot give.

Aerated concrete and gas concrete

Aerated concrete is light and porous. A standard plug or an expansion anchor pushes the material away instead of gripping it, and the load that remains is a fraction of what you are used to in concrete. Here, use fixings that are assessed for aerated concrete, keep large centre-to-centre spacings and edge distances, and spread the load over more points than you would in concrete.

Steel structure

On steel beams you do not need an anchor. A beam clamp such as the TKL clamps onto the flange, without drilling or welding; on sloping beams you use the TKLG. Measure the flange thickness first and choose the clamp to suit. In VdS installations, locking plates are required from DN65.

The choice in three questions

1. What exactly is the base material? Solid concrete, cracked or non-cracked, hollow-core slab, masonry, aerated concrete or steel. If in doubt: a core sample or data from the structural engineer.
2. What does it carry and what happens if it fails? The more serious the consequences, the more strictly you keep to an ETA for that base material and that concrete condition.
3. What must it do in a fire? If the fixing must keep carrying load in a fire, choose an anchor with fire data and calculate with the values from the test report, not with the normal values.

What you record

For each project, keep the ETA and the declaration of performance of every anchor type, note the installation torque you used and take photos of the fixing points before they are covered up. At an inspection, that is the difference between proving and explaining.

Not sure which anchor suits your base material? Describe the situation in the Product finder.

This article is general information, not design advice. The text was checked on 21 October 2026 against the sources below. The design of your installation and the certifying body decide what applies in your project.

Sources

• fischer product page bolt anchor FAZ II Plus (in German)
• fischer product page hammerset anchor FZEA II (in German)
• fischer product page hammerset anchor EA II (in German)
• ETA-19/0520 for the FAZ II Plus (DIBt)
• Product data per anchor in our webshop