Masonry, Concrete Anchors Installed, Fasteners to Use

Light duty – plastic anchors, hammer-set anchors
Medium-duty – concrete screws, Tapcons
Heavy-duty – sleeve anchors, wedge anchors

Masonry and concrete anchors primarily work in either of two ways –  by friction against the sides of the hole, or expanding to grip the concrete.

The type of anchor to use depends on the type of load – shear load and tensile (pull-out) load. Shear load is the weight force exerted parallel to the surface – downward. Tensile load is from force perpendicular to the surface – pulling away from wall. Many loads exert a combination of the two. A fastener used to hang pipes from the ceiling needs tensile strength, while a wall mirror needs shear. A shelf exerts both shear and tensile force.

The hold-strength of anchors depend on the quality of the concrete and on where the anchor is placed. If the concrete will crumble and/or is old, the holding power is reduced. Also, if two fasteners are placed too close together or too near the edge of the masonry, the concrete may break.  For max strength and to avoid splitting the masonry, an anchor should be 5 to 10 diameters away from the edge – a 1/2″ diameter anchor may be 2.5 – 5″ from the edge. However when installing handrails, you need to place the bracket close to the edge of the step so use a plastic anchor, such as an Expandit, and there shouldn’t be a problem.

Due to concrete quality, it is recommended the fastener be rated for at least 4 times the bearing weight for a static load and eight times for dynamic or impact load. And the total of the load must be be divided by the number of anchors.

Masonry drill bits are designed specifically to cut in masonry, cement and stone because they have self-cleaning spiral flutes that remove the material from the hole as it drills. Tapcons come with drill bits sized for their pilot holes.

Hammer drills use a pounding, hammering movement at the same time it is drilling that aids in making holes into hard surfaces. If you have a lot of holes to drill in stone, masonry or concrete, rent or buy a hammer drill.

Sleeve anchors are strong because the expansion of a cylindrical metal sleeve or shield along the length hole makes a larger bearing surface than the wedge anchor, and soft lead forms along the irregularities in the hole and are better than wedge anchors.

Drop-in and self-drilling anchors are two other types of expansion anchors, but aren’t used in masonry because they aren’t embedded very deep and are expanded/set by an impact setting tool. This shallow and hammer-set can cracking or splitting in masonry, leading to failure.

As to Tapcons, they have their uses and limits.
Static loads are from weight that doesn’t move, that exerts the same force – use tapcons.
Dynamic loads are from weights that do move or vibrate, like a machine – don’t use tapcons.
Impact loads happen when weight quickly increases, like when a pallet is load on shelving – don’t use tapcons.