Testing scaffold tie anchors

Scaffolding contractors, supervisors and designers, and the main contractors who check their paperwork: what applies to tie anchors, the two tests, who does them, the records and the kit.

Preliminary tests answer "will this anchor hold in this wall?" They are for when the base material is in doubt, typically brick, stone or timber that the anchor maker has no data for. Five anchors go in for each base material, away from where the scaffold will be, and are thrown away after the test. Each is loaded to twice the tie duty, or three times for nylon anchors unless the maker states otherwise, and passes if it doesn't slip by 1 mm or more. See preliminary tests.

Proof tests answer "were these anchors put in properly?" They are done on every project, on working anchors chosen at random, and the anchors stay in use. See proof testing and test loads by tie class.

At each statutory scaffold inspection. TG4:25 asks the inspector to look at each tie anchor for deformation, damage, rust running from it, and cracks in the wall or its joints. It also says proof tests may be needed again after severe weather or any undermining of the scaffold, testing anchors not tested before where possible and tagging them.

Under the Work at Height Regulations, the scaffold's inspection report is prepared before the end of the working period and a copy given within 24 hours to the person it was done for. It is kept on site until the construction work is finished, then at an office for 3 months. See checking tie anchors during a long job.

Competent people only. TG4:25 asks for competent personnel and a gauge calibrated within the last 12 months to an accuracy of 5%, and NASC's own description of TG4:25 gives trained CISRS scaffolders as an example. Under the Work at Height Regulations, everyone involved in work at height, from planning it to doing it, must be competent; the only exception is a trainee working under a competent person's supervision.

TG4:25 notes that it is common practice to tag each proof-tested anchor with the date and the test load, and says any that failed should be tagged as such, so nobody uses them. Our free scaffold tie test record and tags template has both, or the Staht Connect app records each test with a photo and a map pin.

A brick elevation has 200 standard duty ties, each with a tie duty of 6.1 kN, all put in by one team.

1. Sample. 5% of 200 is 10 anchors, more than the minimum of 3.
2. Load. 1.25 × 6.1 kN = 7.625 kN. TG4:25's own table gives 7.6 kN for this tie.
3. One failure. The rate rises to 1 in 10 for that area: 20 anchors, more than the minimum of 6.
4. Two failures. 1 in 5: 40 anchors, more than the minimum of 12.
5. More than two. Every anchor is tested, and the anchor choice and installation are reviewed.

A failure is serious and is investigated, whatever the count.

A Staht t25 reaches 25 kN, which covers every TG4:25 proof load (4.4, 7.6, 11.4 and 15.3 kN in its table) and preliminary loads up to 24.4 kN for a 12.2 kN tie. Preliminary tests on nylon anchors at three times a 9.1 or 12.2 kN tie are 27.3 and 36.6 kN, beyond a t25: use a t60 for those.

Load the anchor itself through its thread or eye, never through the tie tube. In brickwork, keep the tester's feet off the brick the anchor is in; TG4:25 says the bridge should normally be set vertically to do this. The t25 kit takes threaded and slotted washers from M6 to M16. Hire a t25 for a single job, or buy through Leach's or direct.

• Scaffold tie testing: the kit
• Scaffold tie anchors and anchor types
• Construction: BS 8539 tests by other trades on the same site