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12 בJuly 2026What is a chemical anchor, and what types are there?
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Why does chemical anchoring matter so much in construction today?
To make a connection in construction there are two options: a mechanical connection, or a chemical one. As the technology advances, the chemical connection becomes more and more attractive. In this article we will first look at what a chemical anchor is — also called a chemical plug or a chemical adhesive — then at the types that exist and the advantages of each.
What is a chemical anchor?
It is a threaded rod, or a reinforcing bar (a “dowel”), bonded with a chemical adhesive — commonly called “epoxy”, a legacy of the days when these adhesives were epoxy-based only — into a base material, which may be concrete, hollow block, solid block, asphalt and so on. The adhesive normally has two components, which must be mixed to activate the bond. The mechanism relies on adhesion between the base material and the rod, unlike a mechanical anchor, which relies on friction or expansion.
What chemical anchor technologies are available?
1.Hand mixing. Two different components are mixed by hand from two tubs, in the ratio specified by the manufacturer. The adhesive is poured into the hole you have drilled, the rod is pushed into the adhesive, and you wait for it to cure. (An outdated method, prone to human error in the mixing ratio.)
2.Glass capsules. The capsule is placed into the drilled hole. With hammer-in capsules, the rod is driven into the capsule with a hammer. If the capsule is designed for a rotary installation, the threaded rod is fitted into a drill or rotary hammer and screwed into the capsule.
3.Injection chemical anchor. The adhesive is supplied in a rigid plastic cartridge (some suppliers also offer a foil cartridge), together with a dispensing gun and a mixing nozzle. This is the most common, safest and most accurate technology in use today.
Comparing the adhesive types available on the chemical anchor market
Matching the type of adhesive to the application is critical to the success of the anchoring. Below is a table comparing the main adhesive families, followed by a closer look at each type:
| Adhesive type | Main characteristics and curing time | Durability and suitability for extreme cases | Overall rating |
|---|---|---|---|
| Polyester | The cheapest material, but suitable for most applications. Tends to shrink slightly. | Not intended for heavy loads, or for a wet environment over time. | ✗ Light applications only |
| Epoxy-acrylate | Properties and price identical to polyester. Fast curing times. | Similar to polyester — basic durability. Advantage: a less pungent smell. | ✗ Basic applications |
| Vinylester / hybrid | Relatively fast curing (around half an hour to an hour, depending on temperature), with no shrinkage. | Can also suit extreme cases (seismic action, higher temperatures, diamond drilling and more). | ✓ An excellent, versatile choice |
| Pure epoxy | Slower curing — a very important property when installing large chemical anchors. | Bond properties slightly higher than vinylester, particularly at large diameters. | ★ The best for heavy loads |
1. Polyester
Polyester is the cheapest material, but it suits most applications. Despite the attractive price, it is important to understand that it tends to shrink slightly during curing, and it is therefore not recommended for underwater installations or for critical loads. You will find polyester adhesives both with and without European approvals — some carcinogenic, others benign. This is the cheapest category, and also the most unruly.
2. Epoxy-acrylate
This is a material that is frequently confused with epoxy. It is unjustly regarded as the better material, because in practice its properties are identical to those of polyester — as is its price. The main difference is that these adhesives generally give off fewer pungent fumes during injection (styrene-free), but from an engineering standpoint the advantages are few.
3. Vinylester, or “hybrid”
Vinylester (or “hybrid”) is a more sophisticated adhesive, which can also suit extreme cases — seismic action, higher temperatures, diamond drilling and more. Vinylester-based adhesives have excellent chemical resistance and cure quickly, and they do not shrink inside the borehole, which allows a full bond that seals the hole even in wet conditions. These adhesives generally carry approvals and advanced properties. Even so, you should always check the specific figures for each individual product.
4. Pure epoxy
Epoxy is the oldest family of these adhesives. They achieve the highest load-bearing capacity in the industry, and they are the ideal solution for installing rebar dowels at large embedment depths. In terms of properties they are fairly similar to vinylester, apart from their slower curing — which is a very important characteristic when installing large chemical anchors, because it gives the engineer and the installer a longer working time (gel time) before the adhesive sets completely. Some advanced epoxy adhesives offer slightly higher bond properties than vinylester, particularly at large diameters.
A word of caution — approvals and certification (ETA)
The chemical anchor market is full of products of widely varying quality. There are many types of injection epoxy adhesive, and you will also find far inferior adhesives with no approvals at all. The absence of an approval (such as a European ETA, or a seismic approval) can lead to catastrophic failure under significant loads. Always make sure the adhesive you hold is backed by technical documentation appropriate to the intended use — cracked concrete, uncracked concrete, seismic action, and so on.
Common questions about chemical anchoring
How do you install a chemical anchor in a hollow block (such as Ytong or pumice block)?
When installing a chemical anchor into a hollow block, injecting the adhesive directly will simply cause it to pour away and disappear into the internal voids of the block, without gripping the rod at all. In such cases you must use a mesh sleeve, in plastic or metal. Insert the sleeve into the borehole, inject the adhesive into it, and as the rod is pushed in, the adhesive is forced out through the small holes in the mesh, forming a rigid “plug” that locks the anchor into the material.
What affects the curing time of the adhesive?
The two main factors that determine how quickly the adhesive sets are the type of adhesive and the ambient and concrete temperature. As explained, pure epoxy adhesives cure slowly. In general, the higher the temperature (in an Israeli summer, for instance), the faster the chemical reaction and the shorter the working time. In particularly cold temperatures, curing will be slow — sometimes requiring many hours before the anchor can be loaded.
Does the borehole have to be cleaned before injecting?
It does — without exception. One of the most common causes of anchoring failure is boreholes that were not cleaned. You must use a steel brush and an air pump (blower) to clear the drilling dust from the walls of the hole at least twice. Dust left in the borehole will prevent the chemical adhesive from bonding to the concrete, and can reduce the anchor's load capacity by tens of percent.