How to order ready-mix concrete

An order is a spec, not a quantity

Ring a batch plant with a number of yards and you will be asked five more questions before they can load anything. Have the answers ready and the call takes ninety seconds: how many yards, what strength, what slump, what maximum aggregate size, whether it needs air entrainment, the site address with a note on access, and the time you want the first truck on the ground.

Say the mix out loud the way they write it: "eight yards of 3500 at a four inch slump, three-quarter stone, air entrained, on site at seven." That sentence is the whole order. A contractor who can say it is treated differently by the dispatcher than one who cannot, and dispatchers decide whose truck is late on a busy morning.

Get the quantity right before you get to any of this. The yardage calculator does the slab, the footing calculator rolls the trench into the same figure, and anything small on the same site — steps, a row of piers — belongs in the same order rather than in a second delivery.

Strength: what PSI actually buys you

3000 psi is the ordinary residential mix and it is fine for interior slabs and most footings. 3500 to 4000 is the driveway, garage floor and exterior flatwork number, and in a freeze-thaw climate 4000 with air is the sensible default rather than the premium option. The step from 3000 to 4000 typically costs a few dollars a yard. On a ten yard pour that is the price of a takeaway lunch against a slab that has to last thirty winters, which is why arguing the client down a strength grade is almost never worth what it saves.

Air entrainment is the one that gets missed, and it matters more than the strength number in any climate that freezes. Five to seven per cent entrained air gives the water somewhere to expand into, and without it exterior concrete scales — the surface flakes away in sheets after a couple of winters. It is not visible when you pour it and it cannot be added afterwards.

The corollary is the trap: do not hard-trowel an air-entrained mix. Power-troweling a slab with entrained air seals the surface over the air and lifts it off in patches, which is the delamination and blistering every finisher has seen and half of them blame on the weather. Interior slabs that get a machine finish go without air; exterior flatwork gets air and a broom finish. If one pour has to do both, order two mixes or accept that the interior one is getting a broom.

Slump, and the water somebody will want to add on site

Slump is workability, not quality. Four inches, give or take an inch, suits most flatwork; walls and anything with congested steel want more; a stiff pad on a slope wants less. Ask for what the pour needs and say so on the order rather than fixing it in the chute.

Then hold the line on water. A gallon of water added to a cubic yard raises the slump about an inch and takes roughly 200 to 300 psi off the finished strength, and it increases shrinkage and the cracking that comes with it. Somebody will ask for it — the concrete looks stiff, the crew is tired, the driver has another load waiting. If the mix genuinely needs to move, a water reducer or a superplasticiser from the truck does it without touching the water-cement ratio, and most plants will send a bottle if you ask when you order.

There is a clock on this. ASTM C94 puts the outside limit at ninety minutes or 300 drum revolutions from batching to discharge, and in genuine heat it is tighter. If your pour is going to run past that, order in staggered loads rather than parking three trucks in the street to go off in the sun.

The charges that land after you have quoted

The yard price is the part everybody compares. The rest of the invoice is where the money quietly goes, and every item here is standard, legitimate and almost never mentioned when the quote is written.

Short load fee. Below roughly three to five yards, a delivery does not pay for the truck, and the plant adds a fee — commonly $30 to $150 and sometimes charged per yard under the minimum. This is why the yardage calculator flags it, and why combining the footing, the slab and the steps into one order is worth doing even when it means a longer day.

Standby, or demurrage. You get a free unload window — usually five to seven minutes a yard, so about an hour on a full truck — and after that the meter runs, frequently $2 to $3.50 a minute or $100 to $150 an hour. A crew that is not ready when the truck arrives is paying for the privilege, and it is the charge most often argued about, because it is the one nobody was expecting.

Then the rest of the list: a minimum load charge on small deliveries, Saturday and after-hours rates, an environmental or fuel surcharge on many tickets, a charge for hot water or a cold-weather accelerator, one for a retarder in high heat, and a washout fee if the plant handles it rather than you. Ask your supplier for their current schedule of these once and put them in your price book. Two calls a year is the whole job.

Booking the pour, and the day itself

Book two or three days ahead in the season and a week ahead for anything over about fifteen yards or needing a pump. Monday mornings and the day after a rain-out are the two worst slots in the week to want a truck at short notice, because everybody rained off on Friday is calling for the same one.

Give dispatch honest access information. A loaded truck runs 30 to 40 tons on three axles and will crack a residential driveway, crush a septic field and sink to the diff in a wet lawn. If the truck cannot reach the pour it is buggies, a pump or a conveyor, and all three are decisions to make when you quote rather than at seven in the morning with the crew standing there.

Nominate a washout spot before the first truck arrives and make sure it is yours to nominate. Washout water is strongly alkaline, it is a genuine environmental liability, and "the driver rinsed the chute into the storm drain" is your problem and not his. A lined pit or a bin on site, agreed with the homeowner in advance, is the cheap version of that conversation.

Read the delivery ticket before you sign it. Mix, yards, batch time, water added on site — it is the only record of what you were actually sold, and if the slab is questioned in two years it is the first document anybody asks for. Keep it with the job.

If you run short, and what to do with what is left

Running short mid-pour is the failure this whole page exists to avoid, because the joint where the first load set against the second is a cold joint and it is permanent. That is the reason for waste allowance — 5% to 10%, 8% as a working default — and the reason to order the round yard up rather than down. Half a yard of surplus costs a few dollars. A cold joint through a garage floor costs the floor.

If it happens anyway, the answer is a call to the plant before the last of the load goes down, not after. Some plants can have a small top-up on the road in twenty minutes; whether that beats the setting time depends on how far you are from the yard, which is worth knowing before the day rather than during it.

Have somewhere for the surplus. A spare form, a set of pier holes, a splash pad by the tap — anything that turns a leftover half yard into work you would otherwise do later. It is a small habit and it makes ordering generously feel less like waste, which is what stops people ordering short in the first place.

Put it in the quote so it does not come out of your margin

Everything above is a cost. If it is not on the quote, it is yours. Price the mix you actually intend to order rather than the cheapest one, name the strength on the line item so a client comparing three bids can see that yours is 4000 and somebody else's is 3000, and state what is excluded — pump hire, standby caused by site access, out-of-hours delivery, rock in the trench.

Say how long the price holds, because cement prices move and a quote accepted four months later at last season's yard rate is a job you do for nothing. Thirty days is the normal line. All of this is the same discipline as pricing the job itself, and the line structure is where it goes on the page.