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Cracked concrete and anchoring: frequently asked questions

Anchoring and cracked concrete — frequently asked questions

Is concrete in tension automatically cracked concrete?

Not necessarily. Tension raises the likelihood that a crack will appear, but classifying concrete as cracked depends on the probability of a significant crack appearing at the anchor position after the anchor is installed.

Is old or damaged concrete cracked concrete?

No. Old or damaged concrete is not covered by the European standards at all. It can certainly cause a significant reduction in the load capacity of an anchor fixed into it, but that has nothing to do with concrete being classified as cracked.

Is cracked concrete simply concrete that has cracks in it?

No. Concrete with cracks you can see with the naked eye is unsound concrete, and how an anchor performs in it is not covered by the European standards — we recommend carrying out pull-out tests to assess the anchor's capacity in such concrete. That said, concrete with very fine cracks can be a factor that raises the likelihood of the concrete counting as cracked — because cracked concrete means concrete in which a new crack appears, or an existing crack widens, at the anchor position.

Is concrete in a ceiling cracked?

Not necessarily. Concrete in a ceiling, far from any support, is in tension — which does raise the risk of the concrete being cracked. But in the region of a ceiling close to a support, the concrete is usually in compression. There is also an effect from the length of the anchor relative to the thickness of the concrete: concrete that is in tension on one face is usually in compression on the other, so the zone in which the anchor actually engages, and the type of anchor, both matter.

Is concrete in a floor slab uncracked?

Not necessarily. See the answer about ceilings — a floor can be in tension too.

Is young concrete (less than 28 days old) cracked concrete?

No — there is no connection. Concrete less than 28 days old is not an approved base material for installing an anchor under the European standard at all.

Is Spancrete (spun concrete) cracked concrete?

No. Spancrete is uncracked concrete — but it is better to use anchors designed specifically for it.

If an anchor is approved for cracked concrete, does that make it good in cracked concrete?

Not necessarily. An approved anchor is one that has been tested in cracked concrete. That tells you nothing about how good the anchor is in cracked concrete — only that its capacity in cracked concrete has been measured.

Is concrete in compression always uncracked?

Yes, barring exceptional cases — because concrete in compression generally will not permit a deep crack of the kind that could affect how an anchor performs.

Can the classification of the concrete change according to the type of anchor?

In theory, yes. Once a wedge anchor is installed, its expansion clips create a tension zone at the end of the anchor. That means the region it sits in is in tension even when no load at all is applied to the anchor. A concrete screw (such as the Adit TFE) or a chemical anchor (such as Adit Chemfix100), by contrast, only induce tension in the concrete when tension is actually applied to them. Although the logic is clear — you are better off avoiding a wedge anchor if you want to minimise the chance of a crack forming — we do not in practice distinguish between anchor types. The reason is simply that we have no tools with which to measure the effect of the anchor type on the probability that a crack will appear.

Can an anchor approved only for uncracked concrete be used in cracked concrete?

Under the European standards, no — there is no permission to install an anchor rated for uncracked concrete in cracked concrete. But because the definition of cracked concrete is probabilistic, there are two cases in which we think it is reasonable to disregard the cracked classification: (1) where the load applied to the anchor is in shear only; and (2) where the anchor's pull-out capacity in uncracked concrete is more than three times what is required — because there is no anchor whose capacity in cracked concrete is less than a third of its capacity in uncracked concrete.

Can an anchor's capacity in cracked concrete be tested on site?

It cannot. The case the European standard describes — an anchor installed in a 0.3 mm crack running its full length — is a situation that is almost impossible to reproduce in a standard building. That is also why, in my opinion, genuine cases of cracked concrete are very rare in reality.

Who gains and who loses when concrete is classified as cracked?

Where the concrete is not truly cracked: the supplier gains, because the cost of the detail is multiplied by three; the contractor loses, for the same reason; and the designer loses, because it can force unnecessary complexity into the detail. In the rare cases where the concrete really is cracked, of course, everybody gains.

How do I know whether to design for cracked or uncracked concrete?

“Cracked concrete” does not mean the concrete is visibly broken. It means the anchor sits in a tension zone, where micro-cracks can form around it. As a general rule, slabs and ceilings in tension, and zones subject to dynamic or seismic loading, are treated as cracked concrete; regions in compression are generally treated as uncracked. For the reasoning behind this, see our detailed article on the definition of cracked concrete.

When should I use a wedge anchor rather than a chemical anchor?

The great advantage of the wedge anchor is speed: once the hole is drilled and the nut tightened to the specified torque, the anchor is immediately ready to carry its full load. A chemical anchor, by contrast, requires a wait of hours for the adhesive to cure. So where the installation is dry and clean, in sound concrete, and the programme is tight, the wedge anchor is usually the more economical solution.

Can a wedge anchor be installed in a hollow block wall (pumice or Ytong)?

Absolutely not. A wedge anchor generates very large splitting pressure against the walls of the borehole. Installed in hollow concrete block, or in lightweight aerated block (Ytong), it will burst the block apart from the inside, and the anchor will simply pull out.

Does the borehole need cleaning before a wedge anchor is inserted?

Yes. A mechanical anchor is somewhat more forgiving of dust than a chemical anchor, but drilling dust accumulating at the bottom of the hole will stop the wedge anchor reaching its required embedment depth. Dust can also prevent the expansion clips from opening properly against the concrete. Always pump or blow the dust out before inserting the anchor.

Is the MTP-X wedge anchor approved for seismic use?

Yes. The MTP-X carries the most stringent European approval categories (ETA), including seismic approval in categories C1 and C2. That matters for public infrastructure and engineering projects. Bear in mind that for structural elements under seismic design, a C2 approval is the one required — C1 covers non-structural elements only. See our article on how to interpret seismic approval.

Cracked Concrete and Anchoring — Frequently Asked Questions

The full guide: anchoring and cracked concrete, in a question-and-answer format. What actually counts as “cracked concrete”, when it matters, and how to choose the right anchor for it.

Cracked concreteUncracked concreteWedge anchorMTP-XSeismic C1/C2Micro-cracksFAQ

In short

“Cracked concrete” does not mean concrete with visible cracks, old damage, or young concrete — it means concrete in a tension-stress zone where a new crack may appear, or an old one widen, at the anchor location. Most ceilings, suspended floors and areas subject to dynamic and seismic loads are defined as cracked concrete. Without an explicit instruction from the structural engineer, the safe choice is a cracked-concrete-rated wedge anchor such as the ADIT MTP-X, which carries the strict European ETA seismic approval in categories C1 and C2 — and in Israel every structural design requires C2.

The full guide — anchoring and cracked concrete (FAQ)

Is concrete in tension cracked concrete?

Not necessarily. Tension raises the chance of a crack appearing, but defining concrete as cracked depends on the probability of a significant crack appearing at the anchor location after the anchor is installed.

Is old, damaged concrete cracked concrete?

No. Old, damaged concrete is not covered by the European standards, and although it can definitely cause a significant drop in the capacity of an anchor connected to it, it has nothing to do with concrete defined as cracked.

Is cracked concrete concrete with cracks?

No. Concrete with cracks visible to the eye is not “non-standard” concrete, and the anchor’s function within it is not covered by the European standards — pull-out tests are recommended to assess an anchor’s capacity in it. But concrete with very fine cracks can be a factor that raises the chance of the concrete being cracked, because cracked concrete is concrete in which a new crack appears, or an old crack widens, at the anchor location.

Is concrete in a ceiling cracked?

Not necessarily. Concrete in a ceiling, far from any support, is in tension — a factor that raises the risk of the concrete being cracked. But in an area of a ceiling near a support point, it may not be.

Is concrete in a floor cracked?

Not necessarily. See the answer about the ceiling — a floor can also be in tension.

Is young concrete (under 28 days) cracked concrete?

No, there is no connection. Concrete before 28 days is not an approved substrate for anchor installation under the European standard.

Is Spancrete (prestressed concrete) cracked concrete?

No. Spancrete is uncracked concrete, but it is better to use anchoring designed for Spancrete within it.

Is an anchor rated for cracked concrete good for cracked concrete?

Not necessarily. A rated anchor is one that was tested for cracked concrete. That is no evidence of the bolt’s quality for cracked concrete — only that its capacity for cracked concrete was measured.

Is concrete in compression uncracked?

Yes, with an exception, because concrete in compression generally does not allow the existence of a deep crack that could affect the anchor’s function.

Can the definition of concrete as cracked change according to the anchor type?

Yes, in theory. After a wedge anchor (cone anchor) is installed, its wings create a tension zone at the anchor tip. This means that even when no tension is applied to the anchor, the area where it is installed is in tension. By contrast, a concrete screw (such as the ADIT TFE) or a chemical anchor (such as Adit Chemfix100) apply tension in the concrete only when tension is applied to them. Although the logic is clear — it is better not to use a wedge anchor in terms of the chance of a crack appearing — we do not make it a rule. Under the European standards, you may not install an uncracked-concrete anchor in cracked concrete. But since the definition of cracked concrete is probabilistic, there are two cases where it seemed right to us to ignore the cracked state: (1) if the load applied to the anchor is only in shear; (2) if the anchor’s uncracked-concrete pull-out capacity is 3 times higher than required — no anchor has a cracked-concrete capacity lower than one-third of its uncracked-concrete capacity.

Can you test an anchor’s cracked-concrete capacity in the field?

You cannot, because the case described in the European standard — an anchor installed in a 0.3 mm crack along its whole length — is an almost impossible situation in a standard building. This also explains why the writer of these lines thinks there are very few real cases of cracked concrete.

Who gains and who loses from defining the concrete as cracked?

If the concrete is not really cracked, the supplier gains because the cost of the item is multiplied by 3, the contractor loses for the same reasons, and the designer loses because it can cause unnecessary complexity in the detail. In the rare cases where the concrete really is cracked, everyone certainly gains.

How do I know if I need a “cracked-concrete wedge anchor” or a regular one?

Cracked concrete does not mean the concrete is “broken” to the naked eye, but that it is in a tension-stress zone that can create micro-cracks around the anchor. Under the European standard and the new Israeli standard (T”I), most ceilings, suspended floors and areas subject to dynamic and seismic loads are defined as cracked concrete. If there is no explicit instruction otherwise from the structural engineer, the safe and correct choice is to always use a cracked-concrete wedge anchor (such as the MTP-X) for a maximum safety factor.

When is it better to use a wedge anchor instead of a chemical anchor?

The huge advantage of a wedge anchor (cone anchor) is work speed: the moment you have drilled the hole and tightened the nut to the correct torque, the anchor is immediately ready to carry a full load! With a chemical anchor you must wait hours for the material to cure. So when it is a dry, clean installation on firm, stable concrete with a tight schedule, the wedge anchor is the most economical and efficient solution.

Is it permitted to install a wedge anchor in a block wall (hollow or Ytong)?

Absolutely not! A cone/wedge anchor creates an enormous expansion pressure on the walls of the drilled hole. Installing it in a hollow block, black block or lightweight concrete (Ytong) will cause the block to burst and break from within, and the anchor will pull out easily. For blocks, use a suitable plastic plug (such as the ADIT GX-L), dedicated block Jumbo anchors, or a chemical anchor (such as Adit Chemfix100) with a mesh sleeve.

Must the drilled hole be cleaned before inserting a wedge anchor?

Yes! Although a mechanical anchor is a little more forgiving of the presence of dust than a chemical anchor, an accumulation of drilling dust at the bottom of the hole will prevent the wedge anchor from reaching the required installation depth. In addition, dust can interfere with the correct opening of the expansion clip against the concrete walls. It is always recommended to vacuum or blow out the dust before inserting the anchor.

Is the MTP-X wedge anchor earthquake-resistant?

Yes. The MTP-X model holds the strictest engineering approvals in Europe (ETA), including a seismic (earthquake) approval in categories C1 and C2. This figure is extremely important for public engineering projects and infrastructure structures across Israel. It is important to remember that in Israel every structural design requires a C2 classification, so there is a clear preference for these solutions over other products, such as anchors based on epoxy-acrylate resins, which are usually intended for light-to-medium loads and often come with a C1 standard only.

Sources

  • ADIT MTP-X wedge anchor ETA and seismic (C1/C2) approval data; TFE concrete screw and Chemfix100 data.
  • European anchor design standards and the Israeli standard (T”I) on cracked vs uncracked concrete.