How to Drill into Concrete: Hammer Drills & SDS Bits

Concrete is not a uniform material; it is a matrix of hardened Portland cement paste binding together fine sand and dense, high-hardness mineral aggregates such as granite, river gravel, limestone, or quartz. Pure rotary motion simply scrapes the surface, generating friction temperatures exceeding 1,200°F that melt the copper brazing holding carbide cutter heads.

Not all masonry bits are manufactured equally. The American National Standards Institute (ANSI B212.15) specifies precise outside diameter tolerances for carbide-tipped masonry drill bits. Using off-spec or worn non-ANSI drill bits yields oval or undersized holes, causing wedge anchors to bind prematurely or Tapcon screws to snap off flush with the slab.

Two-Cutter vs. Four-Cutter Heads: Entry-level SDS-Plus bits utilize a single chisel-style carbide tip (2-cutter). While fast in clean concrete, if a 2-cutter bit strikes steel rebar, it immediately binds, twists the operator's wrist, or shatters the tip. Professional 4-cutter (cross-head) solid carbide heads feature four distinct 90-degree cutting edges that grind past rebar collisions without jamming, producing a perfectly cylindrical hole.

Flute Evacuation Design: The spiral flutes on a rotary hammer bit do not cut; they act as an Archimedes screw to hoist pulverization dust out of the borehole. Quad-flute architectures isolate high-velocity dust channels, preventing aggregate dust from packing tightly around the shank and causing thermal binding.

Refer to this contractor takeoff matrix to match required anchor loads, hole diameters, and exact bit specifications in 3,000 to 4,500 PSI concrete:

Achieving clean, perfectly perpendicular holes without bit breakage requires a disciplined step-by-step procedure:

1. Spot Marking & Center Dimple: Never place a carbide tip on smooth concrete and pull the trigger at full speed; the bit will skate across the slab. Use a hardened steel center punch or tap a masonry nail with a hammer to create a 1/16" dimple.
2. Start in Rotary-Only Mode: Position the drill bit perpendicular (90 degrees) into the dimple. Squeeze the trigger at low speed (200–300 RPM) for 3 to 5 seconds to establish an anchor collar before engaging percussion.
3. Moderate Forward Pressure: Switch the tool to hammer mode. Apply firm, steady forward pressure (roughly 15 to 25 lbs of push force). Do not lean your entire body weight into an SDS rotary hammer; pneumatic pistons operate with an internal air spring that requires back-and-forth stroke travel. Excessive force dampens the piston stroke and slows penetration.
4. Execute the "Peck Drilling" Technique: Every 10 to 15 seconds, draw the bit partially out of the hole while keeping the motor running. This ejects compacted rock dust trapped in the flutes, cooling the carbide tip and preventing flute jamming.
5. Hole Cleaning (Vacuum & Blowout): Fasteners fail when torqued into loose silica dust. Insert a wire brush, twist vigorously, and blow out the hole using compressed air or an OSHA-compliant HEPA vacuum nozzle.

Jobsite conditions frequently present concealed obstacles within masonry assemblies:

Striking Reinforcing Steel Rebar: When drilling into structural foundation walls or grade beams, sudden stalling accompanied by high-pitched screeching and bright metallic shavings indicates you have struck #4 or #5 reinforcing rebar. Stop immediately. Never pound a standard 2-cutter SDS bit against rebar. Switch to an SDS rebar-cutter bit running in rotary-only mode (hammer mode shatters rebar-cutter teeth) to core cleanly through the steel bar, then re-insert your masonry bit to finish the concrete.

Drilling Hollow Cinder Block (CMU): Cinder block face shells are only 1-1/4 inches thick. Using heavy rotary hammer percussion against hollow CMU can blow out the backside of the face shell, leaving an enormous conical void that renders mechanical expansion anchors completely useless. Turn off hammer mode or use a lightweight drill when fastening into hollow block webs.

Concrete pulverization produces respirable crystalline silica (quartz dust particles smaller than 5 microns). Inhaling crystalline silica leads to silicosis, lung cancer, and irreversible pulmonary disease. OSHA standard 29 CFR 1926.1153 mandates that contractors control silica exposure using engineering controls under Table 1:

• HEPA Shrouded Dust Extractors: For indoor or repetitive commercial drilling, use a commercial vacuum producing at least 25 CFM per inch of bit diameter, equipped with a cyclonic pre-separator and a certified 99.97% HEPA filter with reverse-pulse automatic filter cleaning.
• Hollow Drill Bits (Internal Extraction): Modern SDS-Plus suction bits feature hollow flutes with intake ports right behind the carbide tip, pulling dust out directly at the point of impact before it enters the air.
• Wet Drilling Containment: When core drilling holes 1-1/2 inches or larger, continuous water injection lubricates diamond segments and traps 100% of silica into slurry. Always connect power through an inline GFCI breaker to eliminate shock hazards.