When fixing items as diverse as simple handrails or structural beams to concrete, brick or stone, you’ll want the right masonry anchor. These are solid and durable fasteners with huge holding strength, ensuring anything that needs to be attached to masonry stays there. Masonry anchors vary in holding strength, where and how they’re used, and the type of masonry they’re best suited to. This ranges from light-duty concrete screws used to attach lighter steel or metal items in solid and cracked concrete to Dynabolt sleeve anchors for medium-duty anchoring in concrete, concrete block and brick. These are just two of the dozens of masonry anchors on the market.
Anchoring heavier items close to edges, at closer spacing distances, or in masonry with questionable holding strength (such as hollow block or brick) requires chemical anchors. These differ from traditional mechanical anchors mentioned above in that they don’t eat into or expand in the substrate. This relieves potential stresses and damage to the substrate, evenly distributes weight across a larger area, and once set, offers considerably better corrosion and heat resistance.
Basics of Chemical Anchoring
Chemical anchoring is a fastening technique in concrete, concrete block, brick and stone. It comprises adhesives acting as bonding agents and fasteners, including anchoring studs or reinforcing bars placed in pre-drilled holes in the base material. The anchoring solution creates a high-strength and lasting bond, able to sustain very high loads. Compared to traditional mechanical anchors like expansion bolts, chemical anchors offer a higher degree of flexibility and the ability to be used in light, medium and heavy-duty applications on different substrates and environments.
Types of Masonry Chemical Anchors
The resin used for anchoring threaded studs or bars comes in three main types – polyester, epoxy vinylester, and pure epoxy resin. These act as the bonding agent between the base material and the fastener. Resins differ in holding strength, curing times and price, leading to different uses in different masonry types. Let’s take a closer look.
Polyester Anchors
Polyester resin is a general-purpose bonding adhesive used in light to medium loads, in solid and hollow brick, concrete, stone and concrete block. Ideal uses are attaching non-structural wood and metal elements, including handrails, electrical conduits, gates, fences, facades, awnings, etc. The resin is quick to cure, is to buy and easy to apply.
Vinylester Anchors
These combine epoxy esters and polyester to produce a versatile and durable anchoring solution. Vinylester anchors have considerably higher holding strength and can be used for structural and non-structural elements in light to heavy-duty applications, and in varying base materials. Ideal uses are for outdoor anchoring, due to the resin’s resistance to water, chemicals and heat, and quick curing times. Additionally, vinylester can utilised in both cracked and untracked concrete, extending its use.
Pure Epoxy
For demanding applications in construction and engineering, pure epoxy anchoring resins offer the highest bonding strength, the best chemical and moisture resistance, and the highest load-bearing capability. The resin is especially suited to anchoring structural elements, including columns and beams in all masonry, but particularly in cracked concrete and hollow concert block. A noticeable advantage is the ability to anchor in both dry and wet settings, in settings with temperature extremes and areas prone to seismic shifts. The long list of positives does come at a cost, with epoxy resins being the most expensive and taking the longest to cure. Ideal uses are anchoring starter and reinforcing bars in foundations, and threaded bars for numerous structural elements.
Other types include acrylic adhesive anchors, favoured for their quick installation, fast curing times and versatility; cementitious anchors used in non-structural anchoring and attaching rebar; and hybrid variants which combine two or more types of adhesives to improve holding strength, curing times or resistance to the elements.
Advantages of Chemical Anchoring
Compared to anchors that are drilled or expand into the substrate on tightening, these anchors show clear advantages:
- Suitability for a range of materials – chemical anchors can be used in all masonry types without the risk of damage or dislodging. They don’t expand or drill into the substrate, risking cracks or fissures that affect load capacities or structural integrity.
- Larger embedding depths – resin can be used with studs in fixed lengths, and bar cut to sizes to suit the application and load. This allows a higher flexibility in embedding depths.
- Close-edge anchoring – securing rails or stairs close to edges can be a challenge with mechanical anchors. Chemical anchors remove risks in base material damage and ensure high load capacities.
- Higher holding strength than the base material – mechanical anchors rely on the base material for holding capacity. Chemical anchors on the other hand offer higher strength, due to the bonding of resin and the metal element covering a larger area, and filling holes in the substrate.
- Better chemical, heat and corrosion resistance – specially formulated resins shield studs, rebar and rods from external factors like moisture, corrosive chemicals and expansion and contraction rates that come with temperature changes. This leads to higher strength and durability.
There are a few reasons that keep builders, contractors and DIY-ers from using chemical anchors in all anchoring jobs. There is more work in applying resins and metal anchoring elements, curing times (especially with high-strength epoxy resin) can impact deadlines, and the higher costs are some drawbacks. They are however suitable for softer materials (hollow brick and block), offer more versatility in placement and spacing, can be used in wet and underwater anchoring, and involve lower stress transfer to base materials.
How It’s Done
Applying chemical anchors is done in defined steps. First, ensure that surfaces are free of debris and dust. Next is the drilling stage. Holes can be drilled using a hammer drill with bits specified in the right diameter. Depths should correspond to anchor lengths and the required embedding depth for the load. Once you’ve drilled the hole, use the range of anchoring accessories (wire brushes and hole-cleaning pumps) to remove any remnants.
Most anchoring adhesives are two-part solutions that need to be mixed to prescribed manufacturer ratios. This means using a container and mixing tool to get the right balance of resin and hardener. If this is too intimidating, premixed, single-use capsules can be used instead. Inject mixed adhesive into the drilled hole using a corresponding applicator gun or cartridge. Insert the nozzle in the hole, and apply adhesive until full.
Follow up by inserting the anchor, This should be done before the adhesive starts to settle. Insert and twist the anchor into the adhesive and ensure it is inserted to the correct embedding depth. Curing or setting times differ, but allow enough time before anchoring. Finish up by removing any residue and clearing holes of excess adhesive.