Concrete screws are specially designed so their threads tap into a pre-drilled hole in masonry such as concrete, mortar joints, concrete block and brick. These screws have a double lead, with an alternating raised and lowered thread with notches cut into the raised threads, as well as a diamond-shaped nail-type point. The design is optimal their intended purpose – for use in light or medium-duty applications, thus eliminating the need for an anchor preset in the substrate. The screws are case hardened to maximize thread strength without making the body of the screw so brittle that the head shears off when driving into hard masonry. These screws can be removed once installed. However, reusing the screw in the same hole is not advisable because of thread wear resulting in decreased grip strength or loss of grip strength all together.
There are now many companies that offer similar products to the original ITW/Buildex Tapcon® brand of concrete screw. To name a few, Hilti has the Kwik-Con®, Powers sells the Tapper®, Simpson Strong-Tie has the Titen®. Generic imported concrete screws are now also readily available and offer reasonable quality but at a much lower cost. Most concrete screws sold today are blue in color to resemble the original Tapcon® screw with the distinct blue corrosion resistant Climaseal® finish.
Concrete screws are available with two head styles: hex washer and countersunk flat head. The hex washer head is slotted while the countersunk flat head has a phillips drive. Both are available in lengths from 1-1/4″ up to 6″ to accommodate the varying thickness of different materials to be fastened.
Concrete Screw Embedment
The maximum embedment into the substrate suggested for concrete screws should be no deeper than 1-3/4″ because the thread effectiveness to tap into the substrate deteriorates as the lead threads begin to wear. Concrete screws also have a minimum embedment of 1″ into the substrate in order to reach maximum effectiveness.
Concrete Screw Length
The minimum length of concrete screw is easily calculated. Add 1″ to the thickness of the material being fastened in order to achieve the minimum embedment of 1″. To determine the maximum length of screw, add 1-3/4″ the thickness of the material to be fastened. Hex head concrete screws are measured from surface under the head to the tip of the screw. Flat head screws are measured from the flat surface of the head to the tip of the screw.
Drill Bits for Concrete Screws
Concrete screws require that a hole be drilled into the substrate before the screw can tap threads. A proper hole size is critical for the screw to sit properly and thus requiring the use of a proper drill bit so that specific tolerances are met. A carbide bit meeting ANSI standards is recommended and should be used in combination with a hammer drill so the proper size and shape hole is formed. The hammer motion breaks up the masonry material and the rotation removes the dust from the hole ensuring the hole meets proper tolerances for maximum grip strength.
Depth of Hole for a Concrete Screw
The drilled hole in the substrate must be a minimum of 1/2″ deeper than the penetration depth of the screw. This will allow ample space for debris created during the tapping process to collect and will ensure that the screw will not bottom out in the hole.
Concrete Screw Installation
- Calculate the correct length of screw to use before installation. The minimum length screw to use is determined by adding the thickness of the material being fastened to the minimum embedment of 1 inch. The maximum length of screw to use is determined by adding 1-3/4 inches to the thickness of the material being fastened. Once you know the dimensions of the screw use a hammer drill and correct ANSI standard carbide drill bit. The hammer drill must be in the hammer and rotation mode before starting to drill..
- Drill a hole to the proper depth. Drill a hole to a depth at least 1/2″ deeper than the screw will penetrate. Set the depth gauge provided with the hammer drill to the required depth. If a depth gauge is not available, wrap tape around the bit at the correct embedment depth.
- Prepare the hole for installation. Using a wire brush, compressed air and/or a vacuum, clean the hole of all dust and debris.
- Insert the concrete screw, first through the fixture then into the hole. Turn clockwise by hand or with a power tool using the correct driver.
- The concrete screw is properly set once the head of the concrete screw is securely fixed against the fixture. Make sure that the screw is not allowed to strip the threads in the substrate by avoiding over-torqueing. Turning the screw by hand the last couple of revolutions can help to prevent this. It also ensures that the screw is tight against the surface of the material being fastened.
To avoid head shearing and or stripping consider the following:
- Drill the hole deep enough to avoid the screw from bottoming out in the hole.
- Clean out and the debris from the hole.
- Do not apply too much torque. Turn the screw by hand the last couple of revolutions.
- If the substrate is too hard, the drilled hole may become tapered towards the end as the drill bit wears down. Try for a shallower embedment or use a different type of fastener such as a hammer drive anchor or split drive anchor.
- The embedment depth is too deep for the substrate. Use a shorter screw.