Concrete Screws (Screw Anchors)

They are screws that are driven directly into concrete or solid masonry, without the need for a plug. The special thread cuts into the substrate and creates a grip, so the fixing is quick and can be removed if needed. They are suitable for fixing profiles, brackets, frames and light supports, not for heavy structural loads without verification.

Use a hammer drill with a bit of the size indicated in the screw's product sheet, and drill the hole perpendicular to the surface. The depth must be the one indicated by the manufacturer, and the hole must be cleaned of dust before insertion. A hole that is too large or too small reduces the grip and can let the screw pull out.

The hex head allows tightening with a spanner or screwdriver and is used when a strong grip is needed, including with a flange. The countersunk head is used when the fixing must sit flush with the surface, to avoid protrusions. The round head is chosen when the screw stays visible and appearance or protection against impacts matters.

Zinc-plated screws are suitable for indoor and dry environments, while for humid, outdoor or seaside environments stainless steel screws are needed. Zinc protects from rust but wears away more quickly in the presence of prolonged humidity. Choose the material based on the environment and on the service life you need from the fixing.

For some light loads and removable fixings, concrete screws are a valid alternative to a plug, because they avoid enlarging the hole and are quicker to fit. For heavy, suspended or safety loads the choice must be made after a technical assessment and according to the manufacturer's sheet. Do not use a screw in place of an anchor without having verified its load capacity.

Aerated concrete is softer and less dense than normal concrete, so screws designed for that substrate are needed. Screws for lightweight concrete have a thread and length different from those for solid concrete. Check on the product sheet that the screw is indicated for the type of substrate before drilling.

If the hole is wider than the indicated size, the thread no longer grips the substrate and the screw spins without tightening. In this case the grip is poor and the fixing can give way under load. If the hole is wrong, do not fill it with improvised materials: drill a new hole in the right position, at an adequate distance from the edge.

Unscrew the screw with a screwdriver or driver, turning anticlockwise with a steady movement, without forcing it. If the head is damaged, use a spanner or pliers suitable for gripping the screw. The hole that remains can be reused with a screw of the right size, or filled with a compatible material.