Scaffold anchor testing proves that the ties holding a scaffold to a building will carry the loads the design relies on, and in the UK it is carried out in line with NASC Technical Guidance TG4:19, Anchorage Systems for Scaffolding. There are two kinds of test. A preliminary test establishes whether a chosen fixing is suitable in the base material and what load it can carry, and it is essential where the anchor manufacturer cannot provide load data for that substrate. A proof test is then carried out on a predetermined proportion of the anchors as the scaffold is erected, applying a defined load to confirm that each one has been installed correctly. Testing is done with a calibrated hydraulic pull tester by a competent person, ideally someone other than the installer, and the results are recorded fixing by fixing. Together, the two tests give documented evidence that the anchorage system is fit for purpose before the scaffold is loaded and used.
Ties are one of the components that keep a scaffold stable, so an anchor that has not been proven is a genuine safety risk. This guide explains what TG4:19 asks for, the difference between the two test types, and the loads involved.
Why scaffold ties are tested
A tie transfers wind and stability loads from the scaffold into the structure it is fixed to. If the fixing pulls out or the base material fails, the scaffold loses restraint, and the consequences can be severe. Because a fixing is only as reliable as the material it is set into and the quality of its installation, and neither can safely be assumed, TG4:19 sets out a testing regime to verify the anchorage on site rather than trusting to specification alone.
This matters most where the substrate is uncertain. Older buildings, mixed masonry, soft or perished brick and unknown mortar all behave differently from the strong concrete an anchor might be rated against. Testing removes the guesswork and produces a record that stands up to review.
Preliminary testing
Preliminary testing is carried out to determine how suitable a fixing is within the base material and to establish its loading capability. It is the step you take when you do not yet know what a given anchor will hold in a given substrate, typically because the manufacturer has no load data for that material.
A sample of anchors is installed and loaded, often to a higher multiple of the intended duty, so that a safe working load for the fixing in that specific base material can be established. The results inform anchor selection and the tie pattern for the rest of the job. Where an anchor and substrate combination is already well documented, preliminary testing may not be needed, but on an unknown or variable structure it is the foundation the whole anchorage design rests on.
Proof testing
Proof testing is different in purpose. Rather than establishing what a fixing can hold, it confirms that installed anchors have actually been fitted correctly. As the scaffold is erected, a predetermined number of the installed ties are tested by applying a defined proof load and checking that the anchor holds without movement.
Under TG4:19, the proof load is commonly set at 1.5 times the required tie duty, meaning the design load the tie has to carry, as Hydrajaws describes for standard fixings. Some fixing types carry different requirements: for nylon anchors, TG4 guidance sets the test load at three times the required tie duty. The load is applied and held rather than taken to failure, so the working anchor is proven without being destroyed. The specific proof load and the sampling proportion are set for the job and should be confirmed before testing begins.
Preliminary versus proof testing
| Preliminary test | Proof test | |
|---|---|---|
| Purpose | Establish suitability and safe load of a fixing in the base material | Confirm installed anchors are fitted correctly |
| When | Before or at the start, on a sample, where no manufacturer data exists | During erection, on a proportion of installed ties |
| Destructive? | Anchors may be loaded to higher multiples to establish capacity | Load applied and held, not taken to failure |
| Outcome | A safe working load for the fixing and substrate | A pass or fail on each tested anchor |
Who should test, and keeping the record
TG4:19 is clear that testing should be carried out by a competent person, and good practice is for this to be someone other than the person who installed the anchors. That may be a colleague at the scaffolding contractor or an independent third-party inspector. In practice, an independent inspector whose sole job on site is testing is often more effective at catching a poorly installed fixing.
Anchors should also form part of the ongoing scaffold inspection regime. If a scaffold needs re-inspecting after an event that could affect its stability, such as high winds or a vehicle impact, the anchors should be checked too. A visual inspection looks for deformation, damage, rust seeping from the joint between fixture and substrate, and cracks in the brickwork or mortar. Results are recorded, ideally as an appendix to the scaffold inspection report, so there is a documented history of the anchorage.
The formal test record is the deliverable that proves the work was done. It sets out the anchor type and size, the base material, the test load applied, the calibration of the equipment used and a clear pass or fail against each fixing, so the data can be reviewed by the principal contractor or a client engineer without ambiguity.
Common questions
What is NASC TG4:19?
NASC TG4:19, Anchorage Systems for Scaffolding, is the technical guidance from the National Access and Scaffolding Confederation covering how scaffold ties and anchors should be selected, installed and tested. It defines the two on-site test regimes, preliminary and proof testing, and is the reference the UK scaffolding industry works to for anchorage.
What is the difference between a preliminary and a proof test?
A preliminary test establishes how suitable a fixing is in a particular base material and what load it can safely carry, and it is used where there is no manufacturer load data for that substrate. A proof test is carried out on a proportion of the installed anchors to confirm they have been fitted correctly, applying a set load and holding it rather than pulling the anchor to failure.
What test load is used for scaffold anchors?
For standard fixings, the proof load is commonly 1.5 times the required tie duty. Some fixing types differ: nylon anchors are tested to three times the required tie duty under TG4 guidance. Preliminary tests may load a sample to higher multiples to establish a safe working load. The exact loads and the sampling proportion are agreed for the specific job before testing.
Who is allowed to test scaffold ties?
Testing should be carried out by a competent person, and good practice is for that to be someone other than the installer, whether a colleague at the scaffolding contractor or an independent inspector. An independent third party focused solely on testing is often more effective at identifying a faulty or poorly installed anchor.
If you need scaffold ties, cavity wall ties or other fixings proven on site, our anchor pull testing is carried out in line with NASC TG4 guidance and BS 8539, with a full test certificate for every fixing. For the wider method, see our guide on what an anchor pull test is, and if your works also involve loading the ground, our guide on plate bearing tests explained covers in-situ load testing.