What designers need to know about chemical anchoring
1.1 Use an approved adhesive. Choose a chemical adhesive that holds a valid European Technical Assessment (ETA/EAD) for your application — threaded rod or reinforcing bar, cracked or non-cracked concrete, and so on. Warning: some suppliers sell adhesives with no European approval, or with an approval intended only for non-structural use. Do not rely on the brand name; check the technical data to confirm the product is genuinely approved for the intended use.
1.2 Perform the calculation. Size the anchorage using the design software supplied by the adhesive manufacturer, or by hand calculation, in accordance with the relevant European requirements.
1.3 Specify clearly on the drawings. State the adhesive name, rod diameter, embedment depth and required drill-hole diameter (or refer explicitly to the manufacturer’s instructions). Referring only to the manufacturer’s instructions protects the designer but can invite installer errors, so stating explicit values is preferred.
Warning — the drill diameter depends on the rod type. With the same adhesive and the same rod diameter, the required hole diameter can differ according to the rod type and the assessment used in design. For example, a Ø12 mm threaded rod under EAD/TR 029 requires a 14 mm hole, whereas a Ø12 mm reinforcing bar under the same assessment requires a 16 mm hole; a Ø12 mm reinforcing bar designed to EAD/TR 023 requires a 14 mm hole. Always check the adhesive’s technical data or consult the supplier’s engineering department.
1.4 Large diameters and diamond drilling. If the design uses rods of Ø20 mm and above and the calculation did not allow for diamond (core) drilling, state this clearly on the drawings. Diamond drilling is not permitted unless it was specifically approved and documented.
1.5 Record the basis of design. Note the relevant approvals in the documentation. Where a situation is not covered by an approval, or is unusual, consult the engineering department of the anchor supplier.
What installers need to know about chemical anchoring
2.1 Use the specified adhesive. Confirm the adhesive supplied is the one the designer specified, and check its expiry date before use.
2.2 Drill to the correct size. Drill the hole to the diameter and depth required by the design.
Warning: do not use diamond (core) drilling without consulting the designer. Diamond-drilled holes have smooth walls that significantly reduce bond strength, so the design must have allowed for this reduction.
Warning: the required drill diameter depends on the rod type. With the same adhesive and rod diameter the hole size can differ by rod type and by the assessment used — for example a Ø12 mm threaded rod under EAD/TR 029 needs a 14 mm hole, a Ø12 mm reinforcing bar under TR 029 needs 16 mm, and a Ø12 mm reinforcing bar under TR 023 needs 14 mm. Check the adhesive’s technical data or ask the supplier.
2.3 Clean the hole. Clean the drilled hole thoroughly with compressed air and a brush. Warning: do not rely on a simple blow-out tube — it neither cleans the hole properly nor protects the operator, and the drilling dust is hazardous to breathe. Some adhesives are less sensitive to imperfect cleaning, but no adhesive can be installed to standard with reinforcing bar in an uncleaned hole.
2.4 Clean especially carefully in weak substrates. Thorough cleaning is particularly important when the base material is weak or friable — such as aerated concrete (Ytong), very old concrete or sand. These substrates give lower strength; anchoring is still performed to European standards but with a smaller safe capacity.
Injecting, setting the rod and curing
2.5 Inject from the bottom. Inject the adhesive from the deepest point of the hole outward to about the middle, so the hole fills without trapping air. Warning: some companies advise injecting from the bottom toward the opening — this is incorrect and can trap air and leave the hole poorly filled. Warning: the most common mistake in chemical anchoring, and the cause of more than half of all failures, is injecting too little adhesive. Never reduce the specified quantity, for any reason.
2.6 Insert the rod by hand. Push the rod in by hand with a slow twisting motion; a little adhesive should be forced out of the mouth of the hole, which shows the hole is full and the installation is correct. If the rod will not go in by hand, either the rod is bent or the hole is the wrong size. For overhead or upward installations wear protective equipment — every falling drop of adhesive can cause irreversible damage — and use a temporary retainer (a wedge or small cap on the end of the rod) to hold the rod until the adhesive begins to cure.
2.7 Allow the adhesive to cure. Wait for full cure — typically between 1 and 10 hours depending on the adhesive. Warning: low temperatures slow curing; for diamond-drilled holes allow roughly 24 hours more. Keep flame and high heat away from chemical adhesives: less sensitive products begin to weaken around 40°C and the best perform up to about 80°C. Consult the supplier’s engineer where needed.