Concrete is the base material that the wedge anchor is designed and manufactured to be installed into. Concrete is solid and hard with its strength capable of being calculated so that the wedge anchor and holding values can be tested. Concrete can be manufactured in different strengths with each batch of concrete at a given strength. This uniformity allows for consistent holding values as well as for straight-line interpolation based on embedment depth and different concrete psi strengths. The uniformity, as well as the quantifiable strength of the concrete, are two features that other base materials, such as brick and block, do not have.
Brick, for example, is fairly porous and may have holes, voids or hollow sections. If the expansion clip is inserted into these areas, the clip will not move and expand and the holding value may be nonexistent. In the case of what would appear to be solid brick, the wedge anchor should not be used because although the brick may look solid, it may be too porous to meet the requirements needed for installing a wedge anchor. Another reason for not using wedge anchors in brick even if the wedge anchor can be expanded is that brick is mortared together with other brick and the holding values may be questionable or at least non-quantifiable. Instead, the Sleeve Anchor is an expansion type anchor that should be considered for fastening to brick.
Block or CMU is a very porous material due to the material they are made from and the large hollow sections manufactured into them. Cinder block is more porous than brick and is not suitable as a base material for a wedge anchor to be installed in. If the wedge anchor was to be inserted into a hole in a block, the expanding anchor clip would attempt to expand, causing the base material to give, break apart and not have enough strength to hold up under the expansion forces. The walls of the block are very thin and do not have enough strength to withstand the expansion forces without spalling or breaking apart. The large hollow sections of the block allow for unsafe areas. If the clip of the wedge anchors would penetrate the hollow section, there would not be proper expansion nor adequate holding values. For fastening to block, the Sleeve Anchor should be considered because it is designed for use in this type of base material.
When fastening into concrete, a wedge anchor needs to be installed into the drilled hole which is equal to the diameter of the wedge anchor being installed. The hole must be drilled using a hammer drill set in the hammer and rotation mode while using a carbide tipped bit that meets ANSI standard. Tolerance between anchor diameter and hole size is critical, therefore an ANSI standard bit will ensure that the proper tolerance is met. Each diameter of wedge anchor that meets minimum holding values has a minimum embedded depth into the concrete at which it must be inserted. This minimum embedment depth is the depth after expansion of the anchor below the surface of the concrete. The wedge anchor can be placed in a hole deeper than minimum embedment depth; deeper embedment in most cases will provide higher holding values. The wedge anchor does not need the bottom of the hole to be properly set. The depth of the hole must be a minimum of 1/4” to 1/2” deeper than the wedge anchor’s embedment depth. This extra space allows for any debris created during the installation process to fall out of the way as the wedge anchor is expanded.
As with any anchoring project, it is important to keep safety in mind and follow instructions carefully. Always remember to wear safety goggles, handle all tools with extra care and follow all technical specifications. This article is meant to serve only as a basic explanation of concrete fasteners. Always refer to manufacturer's instructions or consult a contracting expert during any anchoring project.