A simple field test to determine whether or not a product is made from stainless steel is to put a magnet on the item. If the magnet sticks to the item, it is not made of stainless steel. The 410-grade stainless steel will stick to the magnet even though it is stainless steel of a lower grade. The 410-grade stainless steel resists corrosion in dry atmospheres, freshwater, acids, mild alkalies, food, hot gasses, and steam. Tapcons are coated with Climaseal®. This coating, when applied on top of 410 stainless steel, gives these concrete screws superior rust resistance. This coating is called a thermosetting polyester coating and is a result of a three-step process. First, the concrete screws are cleaned and pre-treated and a zinc overcoat is mechanically applied. Second, the first coating of Climaseal® is applied by dipping each screw into the liquid then spinning each screw. This provides consistent coverage and quality. During the third and final step, the screws are dried in a furnace before the second coat of Climaseal® is applied.
Tapcons are available in two diameters- 3/16" and 1/4". The 3/16" diameter is only available in the flat Phillips countersunk head. The 1/4" diameter has two head styles available- the hex washer head and the flat Phillips countersunk head. Each diameter of Tapcon® screw requires the use of the correct bit that matches the tolerance needed for the concrete screw in order to attain adequate holding values.
The same bit is required for each diameter, as when using the standard blue Tapcon®. For example, the 3/16" diameter concrete screw requires a 5/32" bit and the 1/4" diameter requires a 3/16" bit. The length of the bit needed increases with the length of the screw being used. For both the 3/16" and 1/4" diameter screws, the 1-1/4" and 1-3/4" length uses a 3-1/2" bit. The 2-1/4" and 2-3/4" length requires a 4-1/2" bit length. The 3-1/4", 3-3/4", and 4" length screws uses a 5-1/2" bit length. The 5" long screws require a 7-1/2" bit length.
It is critically important to take into consideration the environment in which the concrete screws will be placed. Many factors must be taken into account. One important consideration is whether the concrete screw will be touching a different type of metal. Another important consideration is that two dissimilar materials will create galvanic corrosion.
Galvanic corrosion is the process through which two dissimilar materials come into contact with each other and either oxidize or corrode. Three conditions must exist for galvanic corrosion to occur. First, there must be two electrochemically dissimilar materials. Second, there must be an electrically conductive path between the two materials. Finally, there must be a path that allows the metal ions to move from the more anodic metal to the more cathodic metal.
When using Tapcons in outdoor applications, it is important to take into account various factors. Some factors that one must consider include: if the Tapcon® will be in a moist environment if there are chemicals in the air and if the screw will be submerged in water or other liquids. All of these factors may increase the potential for rusting to occur.
There are a number of important steps to follow when installing stainless steel Tapcon® screws. As mentioned above, it is critical to use the proper diameter Tapcon® drill bit. The hole size is also critical to achieving the proper holding values in the base material of concrete, brick or block. A hammer drill must be used with the proper bit in order for the hole to be the correct shape for the screw to properly tap the base material. The hole must be drilled a minimum of 1/4" deeper than the screw will penetrate into the base material. This will allow space for all of the dust that is created as the threads are tapping into the base material. The 3/16" flat countersunk Phillips headed concrete screw requires a #2-bit tip and the hex washer head requires a 1/4" nut driver. The 1/4" flat countersunk Phillips headed screw requires a #3-bit tip and the 1/4" hex washer headed Tapcon® requires a 5/16" nut setter.
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.