Essential guide to concrete screws
Concrete screws secure medium-to-high load applications into concrete, solid brick, and stone surfaces. People often refer to them as concrete anchors, concrete bolts, or concrete screw anchors.
They deliver a strong, secure hold while enabling quick and efficient installation, even in tough substrates. You can also install them close to the edge of the concrete without causing deformation.
They are available in different styles for use in different applications.
How do concrete screws work?
Concrete screws are held in place by mechanical interlock. As they are screwed into pre-drilled holes, the saw-tooth threads cut into the concrete and form the mechanical interlock between the screw and the base material. Once installed, they can be adjusted if required, but only in accordance with the installation instructions in the ETA.
When should you use concrete screw anchors?
Concrete bolts or anchors are suitable for all building services applications. For example, for fixing pipe support bracketry or installing fixings for plant and machinery.
Most concrete screw anchors are suitable for use in cracked and non-cracked concrete. In certain cases, they are suitable for dynamic loading such as seismic, fatigue and shock, making them very versatile. Many also have a fire rating, which gives added safety and versatility.
Cracked and non-cracked concrete – what is the difference?
A common question asked is how to choose the right anchor for a specific category of concrete. Concrete is commonly distinguished as either ‘cracked’ or ‘non-cracked’ concrete.
Non-cracked concrete – Concrete zones affected by compressive load, e.g. walls or columns, are generally considered as non-cracked. This means the probability that cracks will form in the concrete after installation are generally considered to be low.
Cracked concrete – Zones affected by tensile load, such as lower member parts of ceilings, are considered to be cracked. This means that over time, cracks may develop through the concrete. Cracks can develop even in reinforced concrete zones affected by tensile loads. Although concrete cracks have widths of around 0.3mm and may be invisible to the human eye, they can have a significant effect on the loading capacity of an anchor. With this in mind, when anchoring into cracked concrete, only anchors that have been tested and approved for use in cracked concrete should be used.
In cases where it is difficult or impossible to confirm that the concrete is non-cracked and will remain non-cracked throughout the service life of an anchor, the rule of thumb is to consider the concrete as cracked. This conservative approach helps ensure a safe and reliable anchor installation.
Types of concrete screw
There are several types of concrete screw anchors, designed for use in different types of applications. Walraven offers the 3 main types shown below.
Hex Head (W-HLX-H)
A concrete screw with a hex head is a heavy-duty self-tapping screw with a pre-pressed washer. It can cut through concrete and stone. The hex head allows firmer tightening than some other options. For solid through-fixing of channel, wall plates and more.
Rod Hanger (W-HLX-N)
A concrete screw anchor suitable for hanging threaded rods from ceiling installations. With a female M8/M10 internal thread and a hexagon drive. For easy fixing of pipe routes, channel fixing, ventilation ducts and more. These self-tapping rod hangers offer a fast alternative to traditional drop-in anchors and are installed in less than half the time.
Pan Head (W-HLX-P/PX)
Pan head anchors are more versatile in application but commonly have lower strength than the hex head alternative due to the lack of head tightening. However, with the flatter head, you receive a flush fix against the surface of the attached material, ideal for fastening channel directly to the ceiling for the installation of pipes or ventilation ducts in concrete and hollow core slabs.
Should I use an ETA approved anchor?
Anchors are often used in safety-critical applications. But what is a safety-critical application, and how important is it to use ETA approved anchors?
The European Technical Approval guidelines define safety-critical applications as being: “Applications in which the failure of an anchor could result in collapse or partial collapse of a structure, cause risk to human life, or lead to a significant economic loss”
Over the past decade or so, there have been several major installation failures resulting in serious injury and death. The most common reasons these occur are:
- Incorrect anchor selection
- Incorrect installation
- Specification changes
These failures have reinforced the need for a controlled and traceable approach to the specification, selection, design and installation of anchors, particularly in safety-critical applications. Under the European Construction Product Regulation (CPR), this approach is based on established assessment and design procedures. Where applicable, anchors should preferably be selected from products covered by a valid European Technical Assessment (ETA), based on the relevant European Assessment Document (EAD). Structural design should follow the applicable European provisions, including EN 1992-4 for anchorages in concrete, where applicable, and installation should strictly follow the manufacturer’s ETA and installation instructions. In the United Kingdom, a comparable approach is addressed by the British Standard BS 8539:2012+A1:2021, with significant industry input from the Construction Fixings Association (CFA).
Selecting the right concrete screw
Choosing the right concrete screw is essential for ensuring a safe, secure and long-lasting fixing. Different concrete substrates, load requirements and installation conditions demand different screw types and sizes. Using the correct concrete screw helps achieve the required load performance, reduces the risk of fixing failure and can speed up installation by providing reliable anchorage without the need for additional components. Selecting an unsuitable fixing can lead to poor performance, costly remedial work and potential safety risks, making it important to match the screw specification to the application and substrate.
We’ve created a 10 point checklist to help you select the right concrete screw anchor for your needs. Download it below!
Concrete screw checklist
What should you consider when choosing a concrete screw for your project? This guide will help you choose the right concrete screw anchor for your needs.
How to install concrete screws
As already mentioned, incorrect installation of anchors, including concrete screw anchors, is one of the main causes of installation failure, which can lead to serious problems and even loss of life. Therefore, it is imperative that manufacturer installation guidelines are followed when installing concrete screws. Full installation instructions can be found within the ETA documentation, but here are some top tips for anchor installation.
5 tips for installing concrete screws
1. Anchors always require a drilled hole. Even though concrete screws have threads, for safe installation, they should always be screwed into a drilled hole.
2. Do not anchor into a bad hole. The drill hole should be created according to the specifications in the ETA. For example, it must be perpendicular to the surface, the correct diameter and depth, avoid any reinforcement and spaced correctly.
3. Ensure the hole is dust-free. If drill dust remains in the hole when you install the concrete screw, you risk being unable to insert the anchor fully into the hole and subsequently causing it to break. For some brands of concrete screw, you should use a special pump to clean the hole. With Walraven’s HLX range of concrete screws, hole cleaning isn’t always necessary. If you use a dust-free drill bit, simply give the drill 3 quick in-and-out actions – no pump required. Always check the ETA for the brand of screw you are using for clear instructions on hole cleaning requirements.
4. Use tools with an appropriate amount of torque and do not overtighten the screws. The ETA will give you specific torque values to guarantee the performance of the screw anchor. If you overtighten the screw or use a tool which is too powerful, you risk breaking the concrete screw.
5. Always take time to plan the installation. Take time to read the ETA installation instructions and brief your team to ensure the concrete bolts or anchors are installed safely and according to the guidelines.
What is Walraven’s concrete anchor product offering?
Walraven’s concrete anchor range includes concrete screws, throughbolts, drop-in anchors, chemical anchors and more. Alongside our product range, we offer technical support and advice to help you at every step of the way if you need it.
In summary, Walraven offers:
- A range of high-load, high-performance mechanical and chemical anchors
- ETA approved range offering peace of mind and compliance with BS 8539:2012+A1:2021
- Fire-rated options
- Seismic options
- Documented installation guidance
- Technical advice available over the phone at any time
- Free anchor design software download to help you carry out anchor calculations specific to your installation and select the right anchor for your needs
