What to Consider When Selecting an Anchor
All anchors do the same thing—fasten together two pieces of material. But there are different anchors for different projects, fabricated from different materials, to fasten different kinds of base materials, and how they are installed differs. With so much to consider and so many choices, selecting the right anchor can be a challenge.
White Cap is here to make choosing the right anchor easy so you can focus more on your business, your jobs, and your crew.
Consider these major factors when selecting an anchor:
The age, type, and strength of your base material determines how an anchor is installed.
- Concrete - The most common base material. If working with lightweight concrete (and masonry), consider age and hardness. Anchors fastened in lightweight materials have 40% less load capacity.
- Masonry - Less strong than concrete, and its consistency varies widely. Mortar strength and anchor placement can determine performance.
- Hollow Base Masonry - Requires special care to fit wall thickness and expansion space. Field installation tests are highly recommended.
- Concrete Block - Anchor performance depends on if the block is hollow, grout-filled, or solid; non-load bearing or load-bearing, where it is placed, and the type of mortar used to hold blocks together.
- Brick - Can be used as load-bearing wall, veneer, or façade. Can be solid or with hollow cores and strengthened with steel rods, rebar, or wire. Use adhesive anchors because of brick’s cavities. Brick is not suitable for powder-actuated fasteners.
- Stone - Popular in buildings. Strength and quality varies greatly from quarries and geological location. Stone is fabricated to specific sizes and shapes. When used for load-bearing walls and façades, use corrosion-resistant stainless steel anchors to tie to the backup wall.
- Clay Tile - Thin clay tile walls require special care; use either a hollow wall anchor opening behind the face shell, or for heavier loads, use adhesive anchors. Powder-actuated anchors are not recommended.
- Steel - The type of anchor you choose depends on the specification application, the type of materials you are joining together (i.e. steel-to-steel, steel-to-wood, etc.) and the total thickness of the material in the connection. An anchor rod, or anchor bolt, is a steel rod that is either cast, set in concrete or grouted into concrete and masonry for the purpose of attaching a steel structure to its foundation, providing both stability and preventing movement of the building.
- Wood - Fasten medium corrosion-resistance class anchors when securing pressure treated (also known as preservative treated) wood. Use either zinc or mechanically-galvanized anchors depending upon the level of wood preservative. See the manufacturer’s specifications on the best type of anchor.
Base Material DimensionsDepth and Width Dimensions of concrete and masonry bases are critical for successful anchor installation. When load is applied to unreinforced and reinforced base materials, cracking and splitting may occur if the base is not thick nor wide enough.
Spacing and Edge Distance affects load capacity. Anchors spaced closely together will lower the individual ultimate load capacities. When anchors are installed close to an unsupported edge, the load direction and distance from the edge will also affect load capacity. A concrete cone type of failure will occur as the load is applied, caused by the compressive forces generated by the expansion mechanism or by the stress created by the applied load.
A first step in developing your project budget is determining costs for items that will need to be purchased. In determining how many anchors and what kind you’ll need for a large scale project, you may want to work with your design professional. They can be very helpful in determining quantities and specify if and where certain types are required.
While a specified anchor may appear more expensive at cost per item, but can save in labor costs due to ease and speed of installation.
You’ll also need to factor in “damage quantities” in your budget. Using a low quality anchor or the wrong installation tool can lead to needing significantly more product, dramatically increasing your budget.
When buying large quantities, talk to your White Cap Account Manager about a bulk discount.
Load Level and Type of LoadAnother major factor in selecting an anchor is the type of load and the level of the load. There are three main load categories: static, dynamic, or shock. Anchors are not one-size-fits-all when it comes to loads.
- Static loads are non-moving constant loads.
- Dynamic loads are normally associated with vibration.
- Shock loads are normally high intensity and instantaneous or periodic.
The material used to make an anchor can strengthen or weaken its load capacity. Anchors made with bolts, threaded rod, steel inserts, rod couplers or other materials should be capable of holding their applied load. These anchors should be installed to the minimum recommended thread engagement.
An anchor’s strength can vary depending upon heat treating, strain hardening, or cold working. Beyond load capacities, use and location are other major factors when determining what materials to use to make anchors. Special materials or coatings to prevent corrosion are necessary when anchors will be used in corrosive environments or fastened with different metals.
Installation ProceduresBefore drilling, always be sure that you and your crew are wearing the appropriate OSHA safety equipment, especially protective eyewear, and when appropriate, using correct silica-dust containment measures at all times.
Proper installation is your key to success. A hole drilled correctly is critical for easy installation and best anchor performance.
Always use the right drill bit type for whatever base materials you’re drilling. Concrete, masonry, and wood drill bits are not interchangeable. It only takes seconds to change bits.
Carbide-tipped bits are preferable for drilling anchor holes in concrete. These bits create rough walls and will prevent the anchor from slipping or moving.
If using a rotary hammer or hammer drill to drill the anchor hole, the hammer’s chiseling impact drills a hole with roughened walls.
When installing anchors into wood, always drive a pilot hole first. Without a pilot hole, when you drive a screw into wood, you’re pushing wood out of the way which leads to splitting, cracking, and weakening over time.
Do not install mechanical anchors in holes drilled with diamond-tipped core bits unless you test to verify performance. Diamond-tipped bits drill holes with very smooth walls can cause some anchors to slip and fail prematurely. Smooth walls will need to be roughened and cleaned before installing anchors.
Adhesive anchors should be tested before installation.
Always drill to the proper depth based on the anchor style based on manufacturer’s specifications.
Note: As in all applications, refer to the specifications to determine the hole size and placement, anchor selection, and that installation meets code.
Follow manufacturer’s recommendations to thoroughly clean debris and dust from drilled holes. Contractors may be familiar with prior standards using compressed air, blow-bulbs, and tube brushes.The blow-brush-blow method is effective, but may cause additional complications. Many contractors are using special hollow-core carbide bits that attach to HEPA vacuums for faster hole-drilling and cleaning, and to be compliant with OSHA Silica Dust Containment regulations.
Effects of Corrosion and Service EnvironmentCorrosion is the destruction of a material due to chemical or electrochemical reactions based upon where and how an anchor is installed. Corrosion costs the construction industry billions of dollars each year.
Chemical corrosion occurs when an anchor is installed in a corrosive liquid or gas substance.
Electrochemical corrosion happens when two metals with different electric potential come in contact with an electrolyte (such as water), the metal with the lowest electric potential will form a chemical reaction. That metal will corrode and make the other metal corrode.
Some ways to prevent corrosion are: use the same or similar metals; separate different metals with insulation, a sealing washer, or a coating; or use anchors and fasteners made from metals that are more resistant to corrosion than the material being fastened.
Refer to the specifications for specific product and installation instructions.
Why Codes and Approvals Are ImportantAs with all construction, it is important to meet approvals, building codes, jurisdictions and listings as outlined by the International Code Council (ICC-ES), Department of Transportation (DOT) Qualified/Approved Product Lists, Underwriters Laboratory (UL), Factory Mutual (FM), LEED Certifications, VOC requirements and others. Review product data sheets and project specifications to ensure you are meeting guidelines.
The fundamentals of anchor design include the determination calculation of design load capacities based on laboratory test data conducted to simulate typical field conditions.