Assembly for chemical anchors - description of the technique

Most of our wall masts are installed using chemical anchors and threaded rods. This is a very convenient and robust technique, nevertheless vulnerable to execution errors. The reactions on the pins especially in the case of taller and more heavily loaded masts reach values counted in tons, so the quality of fastening is crucial.

A general note - if you are not a professional installer or structural engineer - consider ordering a mast statics and anchoring method study tailored to the specific wall you will be working with. The significant forces that can be generated on the mounts can result in scratching or, in extreme cases, tearing out a chunk of the wall along with a properly made anchorage. Some walls are not suitable for the installation of larger wall masts at all, while others require other techniques (e.g. screwing the wall with the "sandwich" technique, i.e. from the inside of the building a channel is installed facing the room with the shelves, a similar one is placed on the outside and the whole thing is screwed through with threaded pins - without the use of anchors). This method of installation bypasses problems with unstable walls (such as damp aerated concrete) or unpredictable walls (various types of hollow blocks and bricks made of pressed or cement-bonded slag - a technique popular in the 1970s). C-rails distribute the load over a much larger area without accumulating point loads.

However, if it can be determined that the wall meets the minimum strength requirements for a given mast and chemical anchors - what remains is the correct anchoring, which is apparently easy - but requires knowledge of techniques and diligent workmanship.

Below you will find a practical guide to installing wall masts using chemical anchors (injection resins) in masonry and concrete. The text takes you "from A to Z," through the preparation of the holes, the selection of accessories, discusses setting times in the context of outdoor temperature and mentions quality control.

Legal Notice: "The Construction Law," on the other hand, requires the use of products with a declaration of performance (CE/DWU) and installation in accordance with technical knowledge and manufacturer's instructions (ETA/EAD, EN 1992-4). Minimum distances and depths are derived from the approvals/ETAs of specific anchoring systems. AluPro does not recommend the use of solutions from any specific manufacturer. The following text is a compilation of practical knowledge, and information from the product sheets of various chemical anchor suppliers. Please note that in the event of a conflict of opinion between the anchor manufacturing instructions included with the product and this guide - the anchor manufacturer's instructions always take precedence.

• System and fixture selection, basic implementation guidelines

The most common distinction is between solid walls (concrete bricks) and those that have different free spaces, e.g. planned - like hollow bricks, or chaotic - like rubble masonry (a mix of brick rubble with unvibrated concrete - often used just after the war in Poland). In the first case, we use impact drilling of a hole larger by about 2 mm than the diameter of the pin to be inserted, in the second case we OBVIOUSLY use baskets for chemical anchors (plastic or metal from a meter). In general, AluPro recommends not to use pins shorter than 150 mm for lightly loaded connections and 250 mm for heavily loaded connections. This is more than the catalog values - but workmanship practice shows that the beginning of the pin (near the wall surface) is rarely properly glued with the mass with the hole, and only from 2/3 of the depth the connection is complete. It is important to remember about the stock of the pin, i.e. after the attachment, washer and screwing the nut - there must be a minimum of 3 turns of thread (or more, it's a matter of aesthetics) sticking out beyond the nut. It is recommended to use self-locking nuts, especially if there is a risk of vibration (e.g., agitation of the truss structure in the wind).

In most cases, we drill the holes with impact drills with an SDS chuck, however, in the case of hollow blocks (especially MAX), we avoid using a hammer. Percussion destroys the internal structure of the hollow block to the point where the anchor may not hold even with the use of a cage, as the internal partitions of the hollow block are broken/crushed.

The key thing is to clean the bottom of the borehole well of dust. Dust in the hole is the most common cause of failed inserts (the situation in which the anchor, despite the passage of time when the nut is tightened, begins to rotate in and out of the hole). The hole should be cleaned by inserting needlepoint all the way to the bottom of the hole, and through this needlepoint the hole should be blown out with a portable compressor - until the dust stops completely.

After inserting the chemistry into the hole, insert the pin in a rotary motion (as if you were screwing it in) - this significantly improves the metal-corner connection. You can "dirty" the pin before screwing it in by rubbing the chemistry into the thread - this will further improve the connection. During screwing in, a situation can occur in which existing air bubbles push the pin out despite being pressed in (the effect of a syringe with a clogged exit). This is the result of a workmanship error of injecting the chemical not from the bottom of the hole but, for example, from the middle of its depth. The situation can be improved by removing and inserting the pin into the hole several times with the hope that the air pocket will find an outlet, or possibly injecting the chemistry deeper.

When conducting anchoring work, there are two things to keep in mind. Anchors are equipped with special two-component anchor mixers. The first several milliliters of anchor is not well mixed and will not form a correct bond. It should be dropped outside the hole. The amount is easy to know by the color. At first you see a predominance of one component, after a while the color stabilizes - this is the moment when you can start injecting.

When the injection is finished, put another few milliliters of the mixture on a bit of cardboard like a so-called "witness". From it we can observe the solidification process of the anchor. At the moment when the witness fully hardens - we can think about the initial loading of the joint. The target load is possible, as a rule, after about 12 hours after anchoring. The outside temperature strongly affects this time, especially the hardening of the witness. Accordingly, the market provides "summer" anchors for working at temperatures above about 10 degrees Celsius and "winter" anchors for working below this threshold. It is worth paying attention to this aspect because the use of a winter anchor in the summer is problematic, the process of setting can and, as a rule, begins to happen already at the time of "screwing in" the pin which disturbs polymerization and reduces the quality of the final connection, in extreme cases does not allow to finalize the installation of the pin. A side aspect is the very rapid setting of the anchor in the mixer, which precludes the use of a single mixer for several holes.

To summarize the key aspects:

Substrate:

• Hollow masonry (hollow block, hollow blocks, blocks with holes): chemical anchor + basket (mesh sleeve). Drilling strokeless (rotational mode).
• Solid masonry (solid brick, cellular concrete, solid blocks): chemical anchor, usually without basket. Rotary percussion drill acceptable (according to manufacturer's recommendations).
• Concrete (ordinary): Chemical anchor without basket; percussion drilling or drilling with dust extraction / pipe drill, according to the instructions.

Resin (example):

• Vinylester/hybrid - Fast setting, wide temperature range, installation in masonry and concrete.
• Epoxy - highest load capacities and longer setting times, less often chosen for applications in wall-mounted mast installation.

Bars/pins:

• Threaded M10-M16 (typically M12 for mast supports), grade 8.8 or stainless steel A2/A4 outdoors. The class and thickness of the pin is part of the development of the anchoring technique - requires consultation with a static engineer
• Wall mast mounts manufactured by AluPro have holes made for pins, these holes are usually 2 mm larger than the suggested pin size, i.e., for example, for an M12 pin the hole is 14 mm, and so on.
• A practical note - it is a good idea to use the mast mount as a template for drilling holes in the wall. After introducing the chemistry into the holes - you can screw in the pins already with the mount in place - which guarantees no spacing problems, but is nevertheless troublesome insofar as the mast mount must be held until the initial solidification of the mix.
• If the mast mount is removed from the wall before pasting the pins, and the pins do not hold the spacing correctly (pasting at an angle, too large holes in relation to the diameter of the pin), it may be difficult or impossible to attach the mount. There are two solutions: not recommended, i.e. reaming the holes in the mast mount to a larger one, or, after the anchor is fully set, bending the rods with a hammer so that they fit into the holes of the mount. In the case of bending, it is worth remembering to do all hammering through a nut screwed onto the end of the pin - which protects the thread of the pin from damage Damage to the thread is a serious problem, because the pasted pin can not be removed, possible re-threading (if possible) will destroy the galvanizing, which will lead to accelerated corrosion. In summary: it is worth avoiding the situation requiring bending of pasted pins, if necessary - only after securing the thread with a nut.

Accessories:

• Mesh sleeves (baskets) for substrates with voids (length adjusted to the depth of the hole). We recommend metal mesh bushings cut from a meter. Plastic bushings, as a rule, have too little depth in relation to the suggested standards. In a metal cage, be sure to plug the outlet of the sleeve either by a special plastic plug or by creasing and rolling the end. It is worth taking care not to distort the roundness of the sleeve during crimping as this makes it difficult to insert it into the hole.
• Portable compressor, compressed air blowing tip, needlepoint or long steel tube
• Bore cleaning brushes - not recommended, although they do exist. Use if the hole cannot be cleaned with compressed air.
• Cartridge gun and a supply of so-called mixers - as a rule, it is possible to introduce chemistry to several holes with one mixer, but the safety rule says - one planned hole = one mixer.

• Spacing and distance planning (s, c, hef)

 In most cases, the mast mounting made dictates the spacing of the holes, so the only issue is to decide how close to the edge of the wall the last hole can be made to have its load-bearing capacity - if applicable and relevant in a given situation. In special cases, the installer must take care of both the minimum distance between holes and the distance from the edge. This matter is regulated by the recommendations of the European Technical Assessment, and it is worth knowing about the proposed minimum values. Their observance guarantees the full strength of each anchor without interdependence of strength with neighboring anchors.

 Definitions:

• hef - The effective anchorage depth of the bar.
• s - spacing between anchor axes.
• c - Anchor axis distance from the edge.

General rule: use ETA (European Technical Assessment / European Technical Evaluation). and manufacturer's tables for a specific resin and rod diameter. Below are typical starting values (for concrete - examples, indicative):

Thread	Bore diameter d0	s_min (min. spacing)	c_min (min. distance from the edge)
M8	10 mm	40 mm	40 mm
M10	12 mm	70 mm	70 mm
M12	16 mm	90 mm	90 mm
M16	20 mm	150 mm	150 mm

 

Masonry (brick/bricks): values often larger than in concrete and depend on the type of block and cage. Accept to start: c_min ≥ 100-200 mm, s_min ≥ 200-250 mm, unless the ETA of a particular system allows less. Always check wall thickness And the arrangement of voids.

Tip: Mount the mast supports so that the holes missed into joints or chambers of hollow blocks with very thin walls. If this cannot be avoided - use a longer basket or change the spacing (if possible).

• Calculation of the length of the rod (pin)

Generally, the length of the bar is determined empirically and AluPro's recommendation is described in the practical advice section. In general, we recommend a minimum value of 150 mm for M10-M12 pins and low loads and 250 mm for M16-M20 pins and high loads. Nevertheless, the problem is described in the literature - below is a brief summary of the theory.

Practical design:

Where:

• hef - according to the manufacturer's tables (typically: M10 ≈ 60-90 mm, M12 ≈ 70-110 mm, M16 ≈ 80-125 mm depending on the system and substrate).
• t_ucht - The total thickness of the base/support + any spacers.
• t_washers+nuts - accept ~15-20 mm For M12 (nut + washer).
• supply - min. 2-3 thread turns Outside the nut (about 5-8 mm for M12).

Example (M12): hef 100 mm + plate 10 mm + (nut + washer) 18 mm + stock 6 mm ⇒. L ≈ 134 mm → we order M12×140.

• Determination and drilling of holes

Here the matter is intuitive and already partially described above. If possible, use the mounts as a template to make the holes, use a level to ensure that the structure is vertical during the fitting, remember to apply the level in two perpendicular planes along the edge of the ballast mast main tube.

1. Routing holes on the wall (following the level). If you have two supports (top/bottom), route both of them once the mast is in place vertical.
2. Drilling:
   • Hollow/hollow wall: concrete drill bit, rotary mode (without impact), so as not to rag the thin walls. Diameter d0 = diameter from the table for the resin/bar/basket in question.
   • Solid masonry/concrete: acceptable impact. Keep perpendicularity; do not "pump" the drill.
3. Hole depth h0 ≥ hef (For baskets - according to their length). Mark the desired depth on the drill with a marker.

• Cleaning the hole - the key to carrying capacity

Dirty hole = poor connection. Perform cleaning just before injection. We partially discussed the problem above - this is one of the most important steps on the road to success. Remember that the hole must be dry, adherent and non-oiled. Some compressors can mix compressed air with oil mist through their leaks, and/or with mist from condensed water in the pressure accumulator. Avoid both of these situations. Check if they occur by blowing compressed air on a dry tissue from a distance for several seconds. Check if it has become damp or oily. Another common problem is that the hole gets wet in the rain. If water gets into the hole-especially in solid concrete-it precludes the correct insertion of the pin until it is fully dry.

Procedure (universal):

• Compressed air: insert tube to the bottom of the hole and blow 2-4× full length (air oil = ban). Typical parameters: ≥ 6 bar, ≈ 6 m³/h. You blow until the dust from the air coming out of the hole is gone
• Brushing: brush matched by diameter to d0; 2-4× Full depth "screwing/unscrewing" motion. If you do not feel the "resistance" - brush too small. Brushing alone is not recommended and is not sufficient to clean the hole, it can be used as a supporting method for cleaning with compressed air
• Re-blow: until no dust flies out.

Hollow/hollow wall + basket: The hole is also cleaned (dust weakens the adhesion of the basket to the wall). Then insert the basket Flush with the face of the wall.

Tip: A hand pump is enough for small diameters (≤12 mm and shallow holes), but for larger diameters and depths, it is necessary to use a compressor.

6) Preparation of resin (cartridge)

1. Set up new mixer, never shorten it.
2. Throw away the first portions (several "shots") until the color of the mixture is homogeneous.
3. If you are installing multiple anchors - keep the cartridge in the operating temperature (e.g., a thermo box) to have a repeatable gel time.

Tip: Any pause = risk of resin freezing in the mixer. After a long pause replace the mixer. The mixer in which the chemistry begins to gel puts an unexpected, greater than normal resistance. If you notice this - replace necessarily.

• Injection and rod embedding

1. Filling from the bottom: you slide the mixer into the very bottom hole/basket and you withdraw it along with serving Resin, without blisters. Usually the filling ≈ 2/3 hole volume. Do a test (as long as you have many holes) and measure how many full shots with the squeeze trigger provides you with the amount of chemistry that does not leak in excess after guiding the threaded rod. Note this value and repeat for subsequent holes.
2. Embedding: enter rod rotation tag hef - Excess resin is supposed to flow out at the inlet (remove it cleanly when it solidifies - you can also pound it with a hammer, if you don't, the mast mount will not sit flush on the wall).
3. Stabilization: if the hole is vertical upwards - use plugs/pistons or temporary support of the bar until gelation (in the practice of AluPro installation, the situation does not actually occur, but this technique is worth mentioning).

Tip: Mark a line on the bar hef - You can see whether the rod has entered the full depth (quality control).

• "Witness" - when you can incriminate
  
  
  • After injection drop a portion resin on painter's tape (or a piece of tin) and describe the time/temperature.
  • Wait until the "witness" reaches hardness close to target (it can not be scratched with a nail or screwdriver). If this happens - you can preload the connection, for example, by lightly tightening the mount to the wall (with your fingers, or a wrench with feeling)
  • Target load permissible only after the binding time specific to substrate temperatures (according to the technical sheet).

Tip: In winter, the "witness" may harden more slowly than the resin in the depths (warmer there). Don't speed up with a heater with a very hot jet - risk of shrinkage and cracking.

• Winter vs. summer - working and binding times (approximate)

Sample scale (typical vinylester resins):

• • +20 °C: working time ~10-15 min, full load after about 60 min.
  • +5 °C: working time ~40-60 min, full load after 2-3 h.
  • 0...-5 °C ("winter" systems): uptime several dozen minutes, full load after 7-20 h.

Check the manufacturer's chart for the resin used. The time depends on temperatures of the construction material, not air.

•  Installation of brackets and wall mast on thermal insulation

For insulated walls, the matter of installation is somewhat complicated. You have two solutions - the preferred one is to remove the insulation (cut for fixings), install directly to the wall, plaster the remaining hole and restore the facade layer. If this mode is not possible for whatever reason - for smaller masts can be used sleeves spacers passing through the insulation layer with a length that corresponds exactly to the thickness of the insulation (never crush Styrofoam or mineral wool).

• Baskets (mesh sleeves) - when yes and when no
  • Apply (mandatory): at all substrates with empties (bricks/hollow blocks, cellular blocks, etc.). The basket converts "chemical" adhesion into mechanical hitch In the walls of the hollow block. There are many illustrations of this mechanism in the product materials of anchor manufacturers.
  • They are not needed: in concrete and masonry full, as long as the ETA/manufacturer so specifies.
  • Basket material:
    • Plastic/plastic - Standard for masonry fixings; lightweight, quick installation, base models are quite shallow for the purposes of wall-mounted masts - we do not recommend their use unless the specific system allows the channel to be extended to the suggested values.
    • Metal mesh - recommended by AluPro due to the fact that the length of the channel can be shaped quite arbitrarily.

Length selection: basket should fill out zone of effective anchorage, which in practice translates into a borehole depth minus a few millimeters.

• Quality control and documentation
  
  • Record: resin batch number, expiration date, installation temperature, diameters and depths, nut tightening torques - provide this information to the Investor with the as-built documentation.
  • Take photos of the "witness" and outflows at the holes (proof of filling).
  • For higher loads - perform a load test of the anchor for pulling out, for example, using a hook scale and a hand chain winch. Obtain the maximum working moment of the anchor load (according to the statics of the mast) Naturally, perform the test at least 24 h after anchoring.
• Most common mistakes

1. 1. No cleaning Or cleaning "half a whistle". You end up with low strength, or the threaded rod "leaves" the hole when you try to tighten it. It may also begin to rotate in the hole along with the nut.
   2. Impact drilling in hollow block - jagged walls, poor load-bearing capacity. To be verified by load test.
   3. Lack of basket in hollow masonry. A very dangerous mistake. Anchoring ostensibly "holds something" but under real load has a high chance of breaking off. An indirect problem is pouring anchor in absurdly large quantities into brick voids (low cost effectiveness)
   4. Too short a rod (no thread on the nut) or too aggressive tightening.
   5. Load before The expiration of the time of full bonding. This is not a big problem, as long as the fastening does not "let go" - the replacement of broken anchoring is quite difficult. As a rule, we lose the ability to redo the hole of the set diameter, there is a need for a thicker pin.

• Quick download (assembly checklist)
  
  
  • System and documents: selected system with ETA/DoP for a given substrate; write down lot number and expiration date cartouche.
  • Substrate: identified (concrete / solid masonry / hollow masonry with block type). For hollow - provided baskets/mesh sleeves appropriate length.
  • Parameters of anchors: matched M (e.g., M12), hef From the manufacturer's tables, s/c (spacing and edge distance) according to ETA.
  • Drilling: diameter d0 and depth h0 ≥ hef; drilling mode selected (rotation in hollow masonry, percussion allowed in concrete/full masonry); mark with marker hef On the rod and depth on the drill bit.
  • Avoiding weak spots: do not hit the joints and thin walls of the blocks; correct the routing if necessary.
  • Cleaning the hole: blow - brush - blow (min. 2-4×), tube to the bottom, air oil-free; at baskets additionally dedusting the walls. Prohibit gluing on a wet hole.
  • Basket assembly (if required): set flush with the face of the wall; for greater depths, connect segments (plastic).
  • Resin injection: from bottom of hole/basket, fill in approx. 2/3; control discharge at the inlet; new mixer; discard the first portions until uniform in color.
  • Embedding the rod: screw in motion to the marker hef; at the "up" holes, use a plug/support until gelling time.
  • "Witness.": a little resin on the tape/blotch with a temperature description; watch the curing.
  • Setting time: wait to fully solidify the sample (different time depending on the temperature of the wall and air) - only then load/tighten.
  • Twisting: foot/support assembly, washer + nut; tightening torque According to the universal tables of screw tightening torques.
  • Documentation: photos of outflows and "witness", record of batches, mounting conditions, applied moments.

 

A brief guide to commercially available versions of chemical anchors:

 1) Polyester (UP)

• Pros: cheap, fast setting, good for light to medium loads in solid wall and in hollow blocks (with basket).
• Minuses: Weakest of the "chemistries"; inferior temperature/fluid resistance; usually no approvals for cracked concrete.
• Variants: from styrene (intense odor, health and safety/fire restrictions) and styrene-free (in use).

2) Vinylester / Epoxy-Acrylate (VE/EA) ← "primary choice".

• Pros: very good carrying capacity, fast binding, wide temperature range, approval for Cracked concrete, seismic C1/C2; it tolerates moisture well.
• Minuses: More expensive than polyester;

3) Pure epoxy (EP)

• Pros: highest load capacities and best flow resistance, great for deep anchorages (rebar), high repeatability; approved for holes damp.
• Minuses: long gelation/curing time (hours, and days in cold weather), highest price; requires temperature discipline.

4) Methyl methacrylate (MMA)

• Pros: extremely fast binding, also works at low temperatures (even
• Minuses: Very intense smell, short working time (it is easy to "miss" the optimal moment of pasting),

5) Hybrids

• Blends (e.g., VE + mineral additives). They behave like vinylester -. treat as VE, see ETA of a particular product, not the name.

6) Injection cement mortars (mineral)

• Niche. Used mainly for rebars in concrete at great depths and high temps. They are not "resin" in the chemical sense; to threaded bolts and hollow masonry/bricks used rarely.

What to choose for wall masts

• Hollow wall/plaster + basket: VE (styrene-free) → fast, strong, predictable.
• Solid masonry/concrete, standard loads: VE.
• Cracked concrete / heavy loads / high working temp. / rebars: EP.
• For winter: MMA or VE (winter version).
• Budget, lightweight fixings in solid masonry: polyester