A lag shield is a type of concrete anchor that is used in a variety of base materials including concrete, brick, and block. A standard lag screw is used to expand the lag shield anchor once it is placed in the hole in the base material. The length of the lag shield is designated as either short or long. The short lag shield anchors are most commonly used in hard, dense base materials while the long lag shield is used in softer, less dense base material. The lag shield anchor is referred to by the inside diameter of the anchor or by the size of the lag screw that gets inserted into the anchor. The lag shield anchor is available in 5 different diameters in both the short and long versions. These diameters include: 1/4", 3/8", 1/2", 5/8" and 3/4". The diameter of the hole to be drilled is larger than the designated size of the lag shield. For example, the 1/4" lag shield requires a 1/2" hole and a 3/4" lag shield will require a 1" hole. Calculating the length of lag screw needed for a job involves adding the thickness of the material to be fastened to the length of the anchor and also adding space for the washers that are used.
When spacing lag shields in the base material, it is important to consider that the expansion forces which are created when the lag shield is set are transferred to the base material. If the lag shields are placed too close together, an interaction occurs between the expansion forces of the lag shields. This may decrease the holding values of both anchors. The industry standard for minimum spacing for any type of expansion anchor is that they should be placed a minimum of 10 anchor diameters from each other and a minimum of 5 anchor diameters away from any unsupported edge. If lag shields are used in applications where the possibility exists for sudden impact or vibratory loads, then the anchor spacing should be increased.
The installation process for a lag shield into concrete, brick or block includes four steps:
1. Drill a hole into the base material using a hammer drill and masonry bit that is carbide tipped. The bit diameter should be the one recommended for the lag shield diameter being used. Drill the hole the length of the lag shield plus 1/2" in order to allow space for any debris or dust created during the installation process.
2. Clear all debris and dust from the hole using compressed air, vacuum, or a wire brush.
3. Insert the ribbed part of the lag shield into the hole that was drilled in the base material. Tap the lag shield with a hammer until it is level with the surface of the base material.
4. Place the fixture over the lag shield making sure the hole in the fixture lines up with the lag shield. Insert the lag screw through the fixture and into the lag shield, turning the screw clockwise until the head of the bolt meets the surface of the fixture. It is important that the lag screw is not over-torqued because this can cause the lag shield to spin in the hole.
Note: In some applications, the lag screw will begin to tighten or torque-up before the lag screw head meets up with the fixture. Should this happen, take a hammer and tap the head of the lag screw back into the hole until it is flush with the fixture being fastened. Use a wrench to re-tighten the lag screw into the lag shield to complete the expansion process.
The installation of a handrail is a very critical application and must be done with great care to make sure that it is erected safely and properly. Contact the department of your city and/or state that would be in charge of building codes. It is imperative that you find out what the codes are and make sure that all codes are understood and followed. These different codes may include allowable height distance from the floor or stairs, the distance from the wall and/or the distance away from the first stair. All of these codes have been placed on the books for a reason and they are there for the purpose of protecting people based on past experience.
If the lag shield is used for attaching a handrail to brick, it can be placed into the brick or the mortar joint. The quality and quantity of the mortar in the joint, the strength of the brick and the quality of the installation determine the holding values of the lag shield. Make sure that when the handrail is fully installed that the lag shields are anchored fully and provide the holding values needed for the particular application.
Lag shields are good anchors to use when attaching a handrail to brick or other base materials. However, it is important to follow all building codes to ensure proper and safe installation of these lag shields. In this specific application, proper installation is very critical because people's safety can be at risk if the installation is not correct.
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.