How do you screw into concrete?

Common screw sizes

3/16 in and 1/4 inconcrete screws

Bit diameter

Set by the fastenermanufacturer instructions

Silica PEL

50 µg/m³8-hr TWA, 29 CFR 1926.1153

Table 1 control, drills

Shroud + dust collectionplus HEPA vacuum for holes

Structural anchors

ACI 318 Ch. 17with an ICC-ES report

Short version

• Concrete screws cut their own threads — no anchor plug, no expansion force, and they back out again.
• The bit diameter is not a judgment call; it is printed in the fastener’s instructions and often sold with it.
• Drill deeper than the embedment so debris has somewhere to fall.
• Clean the hole twice: vacuum, brush, vacuum. Dust is the usual reason a fastener pulls out.
• For anything carrying structural load, the anchor needs an ICC-ES evaluation report and a design under ACI 318.

How do concrete screws work?

Concrete screws cut a thread directly into the wall of a drilled hole. Hardened threads bite into the concrete as the screw advances, so the fastener holds by thread engagement rather than by wedging or expanding against the hole — which is why they can be removed and why they work closer to an edge than an expansion anchor.

The common diameters are 3/16 inch and 1/4 inch, in a range of lengths, usually with a hex washer head or a flat star-drive head. Most carry a corrosion-resistant coating; exterior work and anything in contact with treated lumber needs a coating or stainless material rated for it, and manufacturers state that rating in their literature.

They are a light- to medium-duty fastener. Furring strips, electrical boxes, conduit straps, hose reels, gate hardware, and bottom plates on a slab are the natural jobs. Where an ICC-ES evaluation report covers a specific screw anchor for structural use, the report — not the packaging — is what defines its capacity.

What size hole, and why does the hole need cleaning?

The fastener sets the hole. Every concrete screw and anchor publishes a required bit diameter, a minimum embedment, and a hole preparation procedure, and those numbers are matched to the product; using the next bit up because that is the one in the case removes most of the thread engagement. Drill the hole deeper than the embedment — a half inch is a common margin — so cuttings have somewhere to go instead of packing under the fastener.

Cleaning is where installed capacity is won or lost. Drilling dust behaves like a lubricant for a screw and like a bond breaker for adhesive anchors, and manufacturers such as Hilti publish specific vacuum-and-brush sequences for that reason. Vacuum the hole, run a stiff brush of the correct diameter, then vacuum again. Blowing the hole out with your mouth or with compressed air is the shortcut that ends in a fastener spinning under load.

That cleaning step is also the OSHA-required one: Table 1 pairs handheld and stand-mounted drills with a HEPA-filtered vacuum when cleaning holes.

How do you control the silica dust?

Drilling concrete generates respirable crystalline silica, regulated under 29 CFR 1926.1153 with a permissible exposure limit of 50 µg/m³ and an action level of 25 µg/m³ as 8-hour time-weighted averages. Table 1 lets an employer comply by using the listed controls without separate exposure assessments.

For handheld and stand-mounted drills, including rotary hammers, Table 1 specifies a drill equipped with a commercially available shroud or cowling with a dust collection system, plus a HEPA-filtered vacuum for cleaning holes — and requires no respirator when those controls are used. The standard also bans dry sweeping where wet methods or HEPA vacuuming are feasible, restricts compressed air for cleanup, requires a written exposure control plan, and triggers medical surveillance for employees who must wear a respirator 30 or more days a year.

A homeowner setting four screws is not the regulated party, but the same shroud-and-vacuum setup takes a minute and keeps the dust out of the room and the hole.

Concrete screw, sleeve anchor, wedge anchor, or adhesive?

Anything holding up structure — a ledger, a column base plate, a seismic connection, an overhead attachment — is designed under ACI 318 Chapter 17 using an anchor with a current ICC-ES evaluation report, and installed to the report’s instructions.

General information, not engineering advice. Structural work should be designed by a licensed engineer.

Where should you not fasten?

Stay away from edges and from other anchors. Every anchor publishes minimum edge distance and minimum spacing, because concrete fails in a cone around the fastener and a nearby edge or neighbor removes part of that cone. Setting a wedge anchor two inches from a slab edge is the classic way to blow a chunk out of the concrete during installation.

Know what is behind the surface. Reinforcing steel typically sits under 1.5 to 2 inches of cover per CIP 25, so a deep hole can find it — and drilling into a post-tensioned slab risks hitting a tendon under high tension. Scan before drilling anything structural, and stop when a bit quits advancing.

Match the anchor to the material. Hollow concrete block needs a toggle, a screen tube, or an anchor rated for hollow base material; a wedge anchor in a block face simply spins or cracks the shell. In old, soft, or spalling concrete, no mechanical anchor performs to its rating, and the fix is repairing the substrate rather than upsizing the screw.

How do you drive it without stripping or snapping it?

Use an impact driver on a moderate setting and stop when the head seats. Concrete screws strip the threads they just cut if you keep driving, and a stripped hole is a dead hole — move over an inch and start again rather than trying to force the same one.

Snapping is a hole problem. A screw that binds before it seats is usually in a hole that is too shallow or packed with dust, so the fastener is fighting cuttings rather than concrete. Back it out, clear the hole, and check that you drilled past the embedment depth.

If the head strips before the screw seats, switch to a hand-driven approach for the last turns. And if it seats but spins freely under load, the hole was oversized or the concrete around it is damaged — pull it, move over, and reset.

Common mistakes

• Using whatever bit is in the case — the fastener specifies its bit diameter, and the wrong one removes most of the thread engagement.
• Skipping the hole cleaning — drilling dust is the single most common reason an anchor fails at a load it was rated for.
• Setting anchors too close to an edge — the failure cone runs out of concrete and blows a chunk out on installation.
• Treating a hardware-store screw as a structural anchor — structural anchoring is designed under ACI 318 with an evaluation-reported product.
• Overdriving with an impact driver — the screw strips the threads it just cut, and the hole cannot be reused.