Why anchors are needed
A wood screw holds well in solid wood, but it has almost nothing to grip in a hollow wall. Drywall is a layer of gypsum between paper faces, typically about half an inch to five-eighths of an inch thick, and it crumbles under load. Brick, block and concrete are hard but do not accept a screw’s thread the way wood does. A wall anchor creates a place for a screw to hold, either by spreading the load over a larger area behind the wall or by expanding or gripping inside a drilled hole.
The best fastening point in a hollow wall is almost always a framing member. Where you can reach a stud, using a screw directly into it is usually stronger than any drywall anchor. A stud finder helps locate studs, though it is worth confirming the result by checking in more than one spot. Anchors are for places where there is no framing.
Know your wall
The right anchor depends first on what is behind the surface.
- Drywall or plaster over a cavity. Hollow walls need anchors that grip or spread behind the board. Plaster and lath walls vary and can be brittle, so test and drill carefully.
- Plywood, paneling or thick wood. Often a screw alone works, especially if it reaches a framing member.
- Brick. Hard fired brick, with mortar joints between. Anchors are generally best placed in the brick rather than the softer mortar, though this varies with the job.
- Concrete block. Often hollow inside, with thin walls and open cores. Some anchors work in solid areas, and others are designed for hollow block.
- Poured concrete. Dense and strong, requiring a masonry bit and often a hammer action.
If you are unsure, drill a small test hole in an inconspicuous place and see what comes out: powder, crumbs or a void.
Anchors for hollow walls
Plastic expansion anchors. A simple ribbed plastic sleeve, pushed into a drilled hole. As the screw is driven in, the sleeve expands. They suit light loads such as small frames and lightweight hardware.
Self-drilling threaded anchors. A coarse-threaded anchor that screws directly into drywall, often with a driver and little or no pre-drilling. They are quick and suit light to medium loads in drywall. They can crumble in soft or damaged board.
Sleeve-type (molly) anchors. A metal sleeve that expands and flattens behind the wall as the screw is tightened. They give a firmer hold than plastic in drywall and can bear medium loads. Some can be removed and the screw reused.
Toggle bolts. A bolt with spring-loaded wings that open behind the wall. Once through the hole, they spread the load over a wide area behind the board, so they are typically chosen for the heaviest loads in hollow walls. The trade-off is a larger hole, and the wings are lost if the bolt is removed unless a version designed for reuse is used.
Anchors for masonry
Plastic sleeve anchors for masonry. A ribbed plug used in brick or block for light and medium loads. The drilled hole must match the plug size.
Concrete screws. Hardened screws that cut their own threads into a pre-drilled masonry hole. They are fast and removable, and are widely used for lighter fastening into block, brick and concrete. They require the correct drill bit diameter and depth, as stated on the package.
Sleeve and wedge anchors. Metal anchors that expand against the walls of the hole when tightened. They are used for heavier fixings in solid concrete. Follow the manufacturer’s instructions closely for hole diameter, depth and edge distance.
Adhesive anchors. Bolts or threaded rods set in a hole with a resin. Used for heavy-duty and structural applications; these belong to professionals and engineered installations.
Drilling for masonry anchors
Masonry needs a carbide-tipped masonry bit, and for hard material a hammer drill, or for larger jobs a rotary hammer, speeds the work. The relevant techniques are covered in the article on hammer drilling masonry. Drill to the depth specified, and a little deeper if dust will gather at the bottom of the hole. Cleaning the hole of dust before inserting the anchor improves holding in many anchor types. Different bits are described in the article on drill bit types.
Matching anchor to load
Load comes in two forms. A shelf bracket or a heavy mirror hung on a hook pulls mostly downward along the wall, which is shear. Something pulling away from the wall, like a grab bar or a wall-mounted TV bracket under leverage, is in tension. Many anchors perform better in one direction than the other.
Package ratings are measured under test conditions, with specific materials in good condition. Real walls vary. Use a conservative approach: choose an anchor rated well above the load, use more than one where practical, and avoid close spacing or edges, where masonry can crack. Heavy or moving loads, as with furniture that could tip, are a safety issue.
For anything that carries a person’s weight or could injure someone if it falls, such as a grab bar, a heavy mirror over a bed, or a TV mount, use fasteners into framing wherever possible, follow the product instructions, and consider having a qualified professional do the installation.
Tips
- Check behind the wall first. Wiring and plumbing may be inside. A detector can help, but they are not foolproof.
- Drill the correct hole size for the anchor, and keep the bit square to the wall.
- Use the screw size the anchor specifies. A longer, thicker or thinner screw can reduce holding.
- Do not overtighten. Over-tightening strips plastic anchors and crushes drywall.
- Do not reuse a failed anchor hole. Move over and start again, or use a bigger anchor.
Safety
Wear safety glasses and a dust mask when drilling masonry, because the dust can irritate lungs, and hearing protection if you use a hammer drill. Mark and locate utilities before drilling, and turn off power if you suspect wiring. This guide offers general information, not professional trade advice.