Green and cured concrete are not the same material to a drill. Green concrete is still hydrating: softer, stickier, and it smears instead of cutting clean. Cured concrete is harder and denser and generates far more heat at the bit. Reading which one you are in decides the water, the feed pressure and whether the hole comes out round.

How each one behaves

Behaviour	Green concrete	Cured concrete
Cutting speed	Fast, sometimes too fast	Slow and steady
Bit feel	Grabby, worst at breakout	Hard and hot, glazes if starved
Slurry	Thick and sticky, packs segments	Thin and grey, drains fast
Main risk	Overfeeding and stalling	Glazing and losing diamond
Hole quality	Round, but edges tear	Clean, but can blow out at exit

Drilling green concrete

• Cut feed pressure. In soft material the bit self-feeds; pushing makes it grab and stall.
• Keep water running: sticky slurry packs the segments and the bit spins without cutting.
• Expect breakout: ease off in the last 20 mm and support the far face.
• Do not judge the bit by the hole wall; green concrete tears and looks ragged regardless.
• Check that the concrete is ready for anchors before you torque anything into it.

Drilling cured concrete

1. Start square with light pressure until a full groove is established.
2. Raise feed gradually; if slurry stops and the bit squeals, it is glazing.
3. Dress the segment in abrasive block, or drill a few seconds in abrasive material, to restore cutting.
4. Balance water: too little glazes, too much floods the anchor zone and hides the cut.
5. Ease off in the last 20 mm to avoid a blown-out exit face.

Field test to tell them apart

If the pour date is unknown, drill a 12 mm test hole. Green concrete gives thick sticky slurry and cuts noticeably faster, sometimes in half the time. Cured concrete gives thin grey slurry and consistent resistance. The test costs two minutes and prevents a day of wrong pressure.

Curing timeline and what it means at the drill

"Green" and "cured" are not two states, they are points on a curve. The number that decides how a slab drills is not age but strength, and strength at 3 days is roughly half of strength at 28 days.

Age	Rough strength	How it drills	What to do
1-3 days	30-50% of design	Cuts easily, edges crumble, core can break up	Avoid coring; hand drill small holes only if approved
3-7 days	50-70%	Cuts cleanly but aggregates can pull out	Small cores with light feed, no hammer action
7-14 days	70-90%	Behaves close to cured, slight edge friability	Coring acceptable with reduced feed at exit
28 days+	Design strength	Hard, dense, predictable	Normal parameters

The same bit at the same rpm behaves differently at 3 days and 28 days. A crew that drilled a green slab last week and applies the same feed to a cured slab this week will glaze a segment and wonder why.

Green concrete: rules that avoid damage

• Reduce feed by roughly a third and keep rpm at the low end. Green concrete cuts fast, and fast is the problem: the segment skates before it cuts.
• No hammer action, no impact drivers. Vibration in young concrete opens the bond between paste and aggregate.
• Expect the core to break up. Cap the segment pressure and withdraw every 40-50 mm so the core is not dragged.
• Never wash a green slab with excess water while coring; it can erode the paste at the hole edge and leave a soft rim that will not hold an anchor.
• Anchor tests are not valid on green concrete. A fixing that passes on day 3 can fail at day 28, and the opposite also happens.

The damage done to green concrete is usually at the edge of the hole, not in the hole itself. A crumbled rim means the anchor has nothing to bear on, and no oversize drilling fixes it.

Cured concrete: what actually changes

Cured concrete is harder, denser and more abrasive, and the failure modes change with it. Binders become more about heat and glazing than about crumbling. Water demand goes up with depth, and rebar strikes become the dominant interruption rather than edge friability.

• Hard aggregate demands a crown with a harder bond and a lighter feed than intuition suggests.
• Heat management replaces edge care: cured concrete conducts heat into the segment and glazes it quickly if the flow is marginal.
• Diamond consumption per metre roughly doubles compared with a 7-day slab at the same diameter.
• Cutting time increases, so the plan needs allowance for the rig staying in place longer.

Where the two meet at the same project, put the green pours last and the cured work first. Changing parameters mid-shift for a different pour date is the kind of switch that gets forgotten on the third hole.

Record pour date, test result and settings. On the next pour of the same mix those numbers are the starting point, not a guess.