Adhesive and epoxy anchor installation field guide

What an adhesive anchor is, and why the install is everything

An adhesive anchor is a threaded rod or a length of rebar set into a drilled hole and bonded to the concrete with a structural adhesive, either an epoxy or an acrylic. There is no wedge, no sleeve, no expansion. The element holds because the cured adhesive grips the wall of the hole on one side and the rod on the other. Pull on it and the load passes through that bond into the concrete.

That single fact is what makes the install the whole job. With a mechanical anchor, a sloppy hole still gets some bite from the expansion. With an adhesive anchor there is nothing else holding it. The strength you designed for exists only if the hole was drilled to the right size and depth, cleaned to bare concrete, and filled with properly mixed adhesive that was allowed to cure before anyone loaded it. Miss any of those and the anchor that looks identical to a good one pulls out at a fraction of its rating.

This guide covers adhesive anchors specifically. For the broader choice between cast-in and post-installed anchors and the mechanical types, see the concrete anchor and fastener guide. For setting rebar in fresh concrete and the cover that protects it, see the rebar placement guide. Here the focus is the bonded install and the handful of steps that decide whether it holds.

Adhesive vs mechanical anchors: what is the difference?

A mechanical anchor holds by force. A wedge anchor flares against the hole wall, a sleeve anchor expands, and the friction of that expansion against the concrete is what resists pullout. An adhesive anchor holds by bond. The cured adhesive transfers load along the full embedded length, with no outward force pushing on the concrete.

That difference decides where each one wins. Because an adhesive anchor puts no expansion force into the concrete, it works close to an edge and at tight spacing where a mechanical anchor would split the concrete or break out a cone. It fills an oversized or slightly wandering hole, and it seals the rod against water. The trade-off is the install: a mechanical anchor is set in minutes and loaded right away, while an adhesive anchor demands clean-hole discipline and a cure before it carries anything.

The rule of thumb in the field is mechanical when you need it loaded now and the geometry is generous, adhesive when you are near an edge, in close, doweling into existing concrete, or you need the higher bonded capacity. The concrete anchor and fastener guide lays out the full menu and the cracked-concrete question for both families.

Epoxy or acrylic: which adhesive?

Two chemistries cover most of the work. Epoxy is the high-capacity, slow option. It develops the highest bond strengths, holds up under sustained load and heat better than the alternatives, and is the usual choice for deep embedments, large-diameter rod, rebar doweling, and anything carrying sustained tension. The cost is time and temperature sensitivity. Many epoxies want the concrete at or above 40°F and can take several hours to a full day to reach load capacity, longer as it gets colder.

Acrylic, including the vinylester and hybrid products the trade lumps in with it, cures fast and works in the cold. Where an epoxy might need most of a day, an acrylic can be ready to load in a few hours, and some are formulated to set in concrete down near or below freezing for same-day bolt-up. The trade-off is generally lower sustained-load and high-temperature performance than a true epoxy, so it tends to land on lighter and medium-duty work.

Do not pick by the family name on the tube. The number that matters is the bond strength and the conditions in the product's evaluation report and MPII for the concrete temperature, the hole condition, and the embedment you actually have. A fast acrylic is the right call on a cold morning with a deadline. An epoxy is the call when the load is sustained and the temperature allows the cure. Match the adhesive to the job, the temperature, and the listing, not to habit.

The bond is the anchor

Load in an adhesive anchor travels through two bonded surfaces in series. The adhesive grips the rod, and the adhesive grips the wall of the drilled hole. The weaker of those two interfaces sets the capacity. On a clean install the rod-to-adhesive bond is rarely the problem, because the rod is solid and consistent. The hole wall is where it goes wrong, because that surface is whatever the drilling and the cleaning left behind.

When the concrete wall is coated in drilling dust, the adhesive bonds to the dust instead of the concrete, and the dust shears off the wall under a fraction of the design load. The anchor does not break. It slides out with the adhesive still stuck to the rod and a sleeve of powder lining the hole. That failure surface is the single most common adhesive-anchor postmortem, and it traces straight back to the hole cleaning.

The bond also depends on the full embedded length working. An air void or a partially filled hole means the load that should spread over the whole embedment piles onto whatever length is actually bonded. So the bond mechanism comes down to three things you control on site: a clean hole wall, a rod fully wetted by adhesive, and adhesive that filled the hole with no voids. No bond, no anchor.

Why do you have to clean the hole for an epoxy anchor?

Because the adhesive bonds to whatever lines the hole, and drilling fills the hole with concrete dust. Bond to clean concrete and the anchor reaches its rating. Bond to a film of dust and the dust lets go, taking the anchor with it. Dust left in the hole is the number one cause of adhesive-anchor failure, and it is the easiest one to prevent and the easiest one to skip when the crew is rushing.

Drilling does two things to the hole. It cuts the hole to size, and it packs the wall and the bottom with fine powder. Hammer-drilling with a carbide bit is the common method and the one most MPII are written around. Core drilling leaves a smoother, glazed wall that some adhesives are not rated for or that needs a roughening step, so check the listing before you core a hole for an anchor.

The cleaning is not a wipe and a glance. It is a defined sequence of blowing the loose dust out, brushing the wall to knock the packed powder loose, and blowing again to clear what the brush freed. The exact number of passes, the brush, and the air come from the MPII for that product. Treat the cleaning as part of the structural work, because it is. The hole that looks clean to the eye still has a powder film on the wall that only the brush removes.

Blow, brush, blow: the cleaning sequence

The standard routine is blow, brush, blow, and most MPII spell out how many of each. Blow the hole out with oil-free compressed air to clear the loose dust. Run a stiff wire brush, sized to the hole, in and out the full depth to scrub the packed powder off the wall. Then blow it out again to remove what the brush loosened. Many instructions call for two full cycles of this, and some specify a vacuum drill system instead. Follow the product's instructions, not a generic count.

The brush size is not a detail. A brush too small for the hole spins without touching the wall and leaves the film exactly where the bond has to form. The MPII names the brush diameter for each hole size for that reason. Brushes wear, so a brush that has cleaned a hundred holes may have dropped below the hole diameter and stopped scrubbing. Check it against the gauge the manufacturer provides or replace it on a schedule.

Compressed air has to be clean and dry. Air carrying compressor oil leaves a film worse than the dust, and that contamination kills bond the same way. Use the nozzle and extension that reach the bottom of the hole, because blowing at the mouth leaves the dust packed at the back where the embedment ends. Brush and blow, then brush and blow again, exactly as the MPII reads. This sequence is the most important thing you do on the whole install.

Follow the MPII

The manufacturer's printed installation instructions, the MPII, is the document that governs an adhesive anchor install, and ACI 318 Chapter 17 points to it by reference. The MPII is the folded sheet in the box, and it is not marketing. It is the procedure the product was tested and listed under, so the published capacity is only valid if the anchor went in the way the MPII describes.

The MPII fixes the hole diameter and depth for the rod size, the cleaning method and the number of brush and blow passes, the brush diameter, the dispensing and mixing steps, the gel or working time, the cure time at each concrete temperature, and any torque applied after cure. Change one of those and you are outside the listing, which means the capacity the engineer used in the design no longer applies to what you built.

Treat the MPII as the spec on the wall, not a suggestion. Pull it out before drilling, keep it at the work, and where the install carries sustained tension overhead or horizontally, the inspection regime expects the installer to read and execute it precisely. ACI 318 Chapter 17 sets the design framework and leans on the MPII for the install, so when the two are in front of you, the MPII is the step-by-step the code is requiring you to follow.

Dispensing and mixing the adhesive

Structural adhesive comes in a dual cartridge, two components held apart until they pass through a static mixing nozzle that blends them as you dispense. The mix is what cures. If the two parts are not fully blended, the adhesive sets soft or not at all, and you cannot see it from the outside, which is what makes the first pull through the nozzle the most common quiet defect.

Discard the first part of every nozzle. The lead of the cartridge is always under-mixed, so squeeze several full strokes onto cardboard until the bead runs a single uniform color with no streaks, then start the hole. The MPII gives the amount to discard, often a few strokes or a set length of bead. Use a fresh nozzle on a new cartridge, and use a fresh nozzle any time the work stops longer than the adhesive's gel time, because adhesive setting up in the nozzle will not mix the next pull.

Watch the cartridge temperature too. Cold adhesive is stiff and hard to push and mixes poorly, while hot adhesive gels fast and steals your working time. Most products want the cartridge conditioned to around room temperature before use, separate from the concrete temperature that drives the cure. Condition the tubes the night before on a cold job rather than fighting a stiff cartridge in the field.

Fill from the bottom, leave no air voids

Fill the hole from the bottom up so the adhesive pushes air out ahead of it instead of trapping it. Put the nozzle tip to the bottom of the cleaned hole, start dispensing, and withdraw slowly as the adhesive rises, keeping the tip below the surface of the adhesive the whole way. Fill to roughly two-thirds to half so that inserting the rod brings the level to the mouth without overfilling. A hole filled from the top traps air at the bottom, and that void is unbonded embedment you cannot see.

Set the rod with a slow turning push to the marked depth, which spreads the adhesive around the full circumference and wets the threads. Adhesive should rise and weep slightly out of the mouth around the rod, which is the field sign the hole filled. No weep means the hole was underfilled, so pull the rod, add adhesive, and reset before it gels.

Overhead and horizontal holes will not hold adhesive by gravity, so they need a piston plug or a screen tube and a nozzle extension to deliver adhesive to the back and dispense as the plug is pushed out. The MPII tells you the hole sizes and depths that require the piston plug, commonly the larger and deeper holes. Overhead is also exactly where a void hides, because the adhesive wants to run back out at you, so the delivery method matters more here than anywhere.

How long does an epoxy anchor take to cure?

Cure time depends on the concrete temperature, and the colder the concrete, the longer it takes. The MPII gives a table of full cure times against concrete temperature, and that table is the only number to trust. As a rough sense of scale, many structural epoxies reach full load capacity in the range of several hours to a full day at around 70°F, stretching well past that as the concrete drops toward 40°F. Fast acrylics cut those times and run colder.

Two different clocks are in play and people confuse them. Working time, also called gel time, is the short window after dispensing during which you can still set and adjust the rod, often only minutes and shorter when it is warm. Cure time is the long wait, hours, before the anchor can carry load. You set the rod inside the working time. You do not touch the anchor for load until the cure time has passed.

Do not load before the cure. A rod tightened, a bracket bolted, a line tensioned, all before the adhesive has cured, drags the rod while the bond is still soft and you never get the rated capacity back. On a cold pour the cure can run far longer than the crew expects, so read the table for the actual concrete temperature, not the air temperature, and hold the load off until the time has passed. That patience is the cheapest insurance on the job.

Wet, damp, and water-filled holes

Water in the hole changes everything, and not every adhesive can handle it. A hole can be dry, damp, water-saturated, or standing full of water, and each condition bonds differently. Many products are rated only for a dry hole. Some are listed for damp or water-saturated concrete, and a few are listed for a water-filled hole. Use an adhesive rated for the condition you actually have, at the capacity the listing gives for that condition, because the same product holds less in a wet hole than a dry one.

The trap is assuming the hole is dry because the surface looks dry. Concrete holds water below the surface, holes drilled outdoors or below grade fill from the surrounding concrete, and a hole that was dry yesterday can be wet after rain. Check the hole, do not guess.

When the condition allows it, the cleaning still has to happen, and a water-filled hole may need the water blown or flushed and the cleaning done per a wet-specific procedure in the MPII. The capacity for the wet condition is usually lower, so the design has to use the wet-hole number from the evaluation report, not the dry-hole headline value. Pick the wrong adhesive for a wet hole and the bond never develops, whatever the cure clock says.

Sustained tension, overhead, and creep

The most dangerous adhesive-anchor application is sustained tension in a horizontal or overhead hole, and it earned that reputation the hard way. Adhesive is a polymer, and under a constant pull at temperature it can creep, slowly deforming over months and years until the anchor walks out of the hole. A short-term pull test can pass while the anchor is quietly failing under the load it sees every day.

This is the failure behind the 2006 Boston Big Dig tunnel ceiling collapse, where adhesive anchors holding heavy concrete ceiling panels in sustained tension crept and let go, killing a motorist. The investigation pushed the industry to treat overhead and horizontal sustained-tension anchors as a special case, and the codes followed.

The result is a specific set of requirements that kick in for adhesive anchors installed horizontally or upwardly inclined that support sustained tension load. ACI 318 Chapter 17 requires those installs to be performed by a certified installer and requires continuous special inspection. If your anchor is overhead or horizontal and carries a sustained pull, this is not an ordinary install, and it does not get treated like one. Get the certified installer, get the inspector, and use an adhesive listed and designed for sustained load at the temperature it will see.

Do epoxy anchors need a certified installer?

For adhesive anchors in a horizontal or upwardly inclined hole carrying sustained tension, yes. ACI 318 Chapter 17 requires the installer to be certified, and the recognized program is the ACI/CRSI Adhesive Anchor Installer Certification. That credential is the one inspectors and engineers ask for on those installs, and the requirement is also written into the building code through the IBC.

The certification is not a class you sit through. It is a written exam on adhesive anchoring plus a hands-on performance test, where the candidate has to read a generic MPII and install an anchor correctly both vertically down and overhead, including a blind overhead install where you cannot see the hole fill. That overhead blind test exists because that is the install that killed someone, and the certification is built around proving the installer can do it right where it counts.

For ordinary anchors set vertically into a floor or a wall carrying short-term load, the certified-installer mandate generally does not apply, though a project spec can still require it. The hard line is the overhead and horizontal sustained-tension case. If you are running that work without a certified installer, you are outside ACI 318 Chapter 17, and an inspector who knows the trade will stop the job.

Do epoxy anchors need special inspection?

Adhesive anchors in horizontal or upwardly inclined holes supporting sustained tension load require continuous special inspection under the IBC, meaning the inspector watches the install as it happens rather than checking it afterward. For an adhesive anchor that is the only way to verify it, because once the rod is set you cannot see whether the hole was clean, whether it filled, or whether the adhesive mixed.

Continuous inspection on these anchors means the special inspector confirms the hole diameter and depth, watches the cleaning sequence, checks the adhesive and the rod against the listing, verifies the cartridge is in date and conditioned, and watches the dispensing and the set. The inspector is checking the install against the MPII and the approved evaluation report. The proof of a good adhesive anchor is the process, since the finished anchor hides everything that matters.

Other adhesive anchors usually fall under periodic special inspection per the IBC and the project's statement of special inspections, with the continuous requirement reserved for the overhead and horizontal sustained-tension case. The exact triggers and frequency come from the adopted IBC edition, the approved evaluation report, and the project documents, so confirm what the job actually requires rather than assuming. The one rule that does not move is continuous inspection for overhead sustained tension.

Doweling rebar into existing concrete

Adhesive anchoring is how you tie new concrete to old. Drilling and bonding rebar into existing concrete, called doweling, lets you extend a slab, add a wall, or connect a new pour to a structure that was finished years ago, developing the bar through the adhesive bond instead of a hooked or lapped bar cast in place. A doweled bar can reach close to the strength of a cast-in bar when the embedment, the adhesive, and the install are right.

The embedment depth is the design number here, and it is usually deeper than a simple anchor, because the bar has to develop enough bond length to act like reinforcement. The engineer sets that depth and the bar size from the adhesive's evaluation report, and you drill and clean to it like any adhesive anchor. Everything from the hole cleaning to the fill to the cure applies the same way, and a doweled bar is just as ruined by dust in the hole as a threaded rod.

Watch what the new hole runs into. Drilling deep into existing concrete you will hit the existing reinforcement, and cutting through it weakens the structure you are tying into. Locate the existing bar before drilling and adjust the hole, rather than grinding through rebar. For how that existing bar was placed, the cover that protects it, and how reinforcement develops, see the rebar placement and cover guide.

Edge distance, spacing, and embedment

Three geometric numbers set the capacity alongside the bond: how deep the rod goes, how far it sits from a free edge, and how close it sits to the next anchor. All three come from the design, drawn from the adhesive's evaluation report, and none of them are field calls. Drill shallower than the specified embedment and you have cut the bonded length and the capacity. Set the anchor closer to an edge or to its neighbor than the design allows and the concrete can break out before the bond is even tested.

Adhesive anchors do better near edges and in close than mechanical anchors, because they put no expansion force into the concrete, and that is a real advantage when the layout is tight. It is not unlimited. There is still a minimum edge distance and a minimum spacing in the listing below which the concrete cone or the edge governs and the capacity drops, sometimes sharply.

Mark the embedment depth on every rod with tape or a paint line before you set it, so you can see it reach the bottom and so the inspector can see it too. Hold the drilled layout to the design dimensions for edge and spacing. When the field condition will not allow the specified geometry, that is a question for the engineer, not a number to fudge at the hole.

The evaluation report and cracked vs uncracked concrete

Every listed adhesive anchor carries an evaluation report, commonly an ICC-ES ESR, and that report is where the real numbers live. It gives the bond strengths, the approved rod and bar sizes, the hole and embedment ranges, the temperature limits, the wet and dry conditions, and whether the product is qualified for cracked concrete, all derived from testing under the acceptance criteria for adhesive anchors. The design uses the ESR values for the actual conditions, and the install has to stay inside the ESR and the MPII for those values to hold.

Cracked versus uncracked concrete is the question that catches people. Concrete in tension zones cracks under service load, and a crack running through an anchor hole cuts the bond where it crosses. An adhesive qualified and designed for cracked concrete accounts for that with reduced values. One qualified only for uncracked concrete cannot be used where the concrete will crack, because the rating assumes a continuous bond the crack destroys. Most structural locations have to assume cracked concrete unless analysis shows otherwise.

This is the engineer's call, not the installer's, but the field has to install the specific product the design was based on. Substituting a different adhesive on site, even a similar one, voids the design, because the new product has a different ESR with different numbers. Install what the drawings and the submittal called out, and if the product on the truck is not that one, stop and get it approved.

Proof and pull testing

Where the project or the engineer calls for it, installed adhesive anchors get proof-load tested, pulled to a specified load to confirm they hold without movement. A proof test is not pulled to failure. It applies a defined load, often a multiple of the service load or a fraction of the design capacity, and the anchor passes if it carries that load without slipping or displacing beyond a small allowance.

Proof testing is common on doweled rebar, on anchors where the existing concrete is unknown, and as a quality check on a sample of production anchors. The engineer sets the test load, the acceptance criterion, and how many anchors to test, since pulling all of them is rarely practical or necessary. A sampling plan with a defined load is the usual approach.

Understand what a short-term proof test does and does not prove. It confirms the anchor was installed well enough to hold that load right now. It does not prove the anchor will resist sustained tension over years, because creep is a long-term behavior a quick pull cannot see. That gap is exactly why overhead sustained-tension anchors lean on the certified installer and continuous inspection rather than on a proof pull alone.

Shelf life and storage

Adhesive has an expiration date printed on the cartridge, and expired adhesive does not cure to its rated strength. Check the date before you open the box. Expired product gets thrown out, not used up to save a tube, because an anchor set with dead adhesive looks identical to a good one and fails the same way dust does.

Storage drives whether the adhesive lasts to that date. The products want a cool, dry place within a temperature range on the label, and heat in particular shortens the life and can start curing the components in the tube. A cartridge that cooked in a truck cab all summer may be no good well before its printed date. Store the cartridges the way the label says, and rotate stock so the oldest goes first.

Condition the cartridge to working temperature before use, which is a different step from storage. Cold adhesive mixes poorly and pushes hard, so a tube pulled from a cold trailer needs to warm to roughly room temperature before it dispenses a proper mix. Keep that conditioning separate in your head from the concrete temperature that controls the cure. One readies the adhesive to dispense, the other sets how long until you can load it.

Anchoring equipment into an existing slab

Setting equipment on an existing slab is where adhesive anchors earn their place, because the slab is already poured and cast-in anchors are not an option. Generator skids, transformers, switchgear, racks, and mechanical units all get anchored to existing concrete after the fact, and the adhesive anchor is the common way to do it near the edges and in the tight bolt patterns that equipment bases come with.

On a data-center or industrial floor the slab may already be crowded with conduit, post-tension cables, and reinforcement, and the layout has to dodge all of it. Locate what is in the slab before drilling, because hitting a post-tension tendon is a serious event and cutting reinforcement weakens the floor. Scan, then drill. The equipment base also tends to be heavy and sometimes vibrating, so the design accounts for the sustained and dynamic load, and that can push you toward an epoxy and toward the inspection requirements rather than a quick set. Match the anchor to the load the equipment actually delivers, not just its weight at rest.

Common mistakes

• Leaving dust in the hole, the number one failure, by skipping or shortcutting the brush-and-blow cleaning.
• Not following the MPII, which puts the install outside the listing the capacity was based on.
• Trapping air voids by filling the hole from the top instead of from the bottom up.
• Loading the anchor before the adhesive has cured for the actual concrete temperature.
• Running overhead or horizontal sustained-tension anchors without a certified installer or continuous special inspection.
• Using expired adhesive, or product that cooked in storage and lost strength before its printed date.
• Using a dry-hole adhesive in a wet or water-filled hole, or a cold-sensitive epoxy below its temperature range.
• Dispensing without discarding the under-mixed lead of the nozzle, so the adhesive sets soft.
• Substituting a different adhesive than the one the design and ESR were based on.

Field checklist

What to document

An adhesive anchor hides its own quality once the rod is set, so the record is the only evidence the install was done right. The inspector signs off on what was watched and recorded, and six months out when something is questioned, the record is what answers whether the anchor was ever sound.

Capture the product and the cartridge lot number, the expiration date, the concrete temperature, the hole condition, the rod or bar size and the embedment, the cleaning method used, the cure time allowed before loading, the installer and whether they were certified, the inspection that covered it, and any proof-test loads and results. On a sustained-tension overhead install the continuous inspection record is the proof the code wanted.

Standards and references

ACI 318 Chapter 17 is the design framework for anchoring to concrete, adhesive anchors included, and it references the manufacturer's printed installation instructions for the install itself, which is why the MPII carries the weight it does. Chapter 17 is also where the requirements for adhesive anchors in horizontal or upwardly inclined holes under sustained tension live, including the certified-installer and special-inspection mandates. The exact section numbers move between code cycles, so confirm them against the adopted edition before citing them on a submittal.

The installer credential is the ACI/CRSI Adhesive Anchor Installer Certification, required by ACI 318 Chapter 17 and by the IBC for the overhead and horizontal sustained-tension case. Special inspection of adhesive anchors is governed by the IBC, continuous for that sustained-tension case and periodic for others, with the specifics in the adopted IBC edition and the project's statement of special inspections.

Product qualification and the design values come from an ICC-ES evaluation report, an ESR, developed under the ICC-ES acceptance criteria for adhesive anchors, AC308. The test methods behind anchor qualification trace to ASTM standards such as ASTM E488 for the strength of anchors in concrete and ASTM E1512 for testing bonded anchors. Cite the document that controls the point, hedge the section numbers to the adopted edition, and let the ESR and the project specification override any rule of thumb. The three things that decide an adhesive anchor, every time, are the hole cleaning, following the MPII, and the certified installer where the code requires one.

Units, terms, and conversions

Adhesive anchoring carries a few terms and unit forms that read differently across a drawing set, a product sheet, and an evaluation report, so it helps to keep them straight.

An adhesive anchor is also called a chemical anchor, a bonded anchor, or an epoxy anchor, though epoxy is only one of the chemistries. Embedment depth shows up as h-ef in the design and reports, given in inches on US drawings and millimeters on metric sheets. Bond strength is a stress, pounds per square inch or megapascals. Hole diameter and rod diameter track the rod size, in inches or millimeters. Concrete temperature, which drives the cure, is the temperature of the concrete itself, not the air, and reads in °F or °C.

Adhesive / chemical anchor

A rod or rebar bonded into a drilled hole with structural adhesive; strength is the bond, not expansion

MPII

Manufacturer's printed installation instructions, the install procedure ACI 318 Chapter 17 references

Bond strength

The stress the cured adhesive transfers between the rod and the concrete wall, in psi or MPa

Embedment (h-ef)

The bonded depth of the rod or bar in the concrete, set by the design from the ESR

Gel / working time

The short window after dispensing during which the rod can still be set and adjusted

Cure time

The longer wait, dependent on concrete temperature, before the anchor can carry load

ESR / AC308

The ICC-ES evaluation report and its acceptance criteria, where the design values and conditions live

Cracked concrete

Concrete in a tension zone that cracks under load; an adhesive must be qualified for it to be used there

Related tools

Calculators and readiness checks for this work

Compare your options

FAQ

People also ask

• What is the difference between a mechanical and an adhesive anchor?
• What is the minimum concrete cover for rebar?
• Cast-in vs post-installed anchors: which should I use?
• Why do data centers need seismic anchoring?
• What is architectural millwork?