How to Invoice After Garage Slab Concrete Work

Short answer: How to invoice after garage slab concrete starts with two yardages, not one. A 24 by 24 bay is 576 sq ft, so 576 ÷ 81 is 7.11 cu yd of 4 in slab, and a 12 in wide turndown running 8 in below it adds 2.37 cu yd across 96 linear feet — about a third again on the same footprint. Then separate lines for base and compaction, vapor barrier, steel, the access method, joint cutting by the linear foot, and the finish. Collect at the tailgate.

A garage slab is the one flatwork job where the concrete is the easy part. It sits inside walls or against a stem wall, it carries a vehicle, it has to drain toward a door, and half the cost is in things that get buried before anyone sees them. The invoice has to make the buried half visible. The format of the document itself is covered in what to include on an invoice, and the question of when the deposit, the progress bill, and the closing bill each go out is worked through in when should a concrete contractor invoice. This is what the closing bill looks like.

What goes on a garage slab invoice that a driveway invoice never has?

Six lines, and every one of them exists because a garage slab is a floor inside a structure rather than a surface in the open.

Line	Unit billed	Why a driveway never has it
Isolation joint at the perimeter	Linear feet of wall	The slab has to float free of the stem wall or footing so the two can move separately
Thickened edge or turndown	Cubic yards, separate from the slab	Carries the wall load or the edge of the bay where no footing exists
Vapor barrier and taped seams	Square feet	Nothing under a driveway needs to stay dry
Slope to the overhead door	Included in grading, called out by fall	Water that gets in on a wet tire has to leave on its own
Sleeves and blockouts	Each	Floor drain, radon vent, conduit stub for an EV charger, a future sink drain
Apron and the transition joint	Square feet plus linear feet	Where the new slab meets the existing driveway at the door opening

Write the bay dimensions on the invoice, not the phrase “garage floor.” A detached 24 by 24 and an attached third bay are different jobs, and in eighteen months when the customer calls about the other building, the dimension line is the quote.

Where do the yards on the invoice come from?

From two calculations that get added, which is why garage slab orders surprise people who only ever priced flatwork.

Volume is square feet times thickness in feet, divided by 27. For a 4 in slab the shortcut is square feet ÷ 81.

Component	Arithmetic	Yards
24 ft × 24 ft slab at 4 in	576 ÷ 81	7.11
Same slab at 5 in	576 × 0.417 ÷ 27	8.89
Turndown, 12 in wide × 8 in below slab, 96 lf	1.0 × 0.67 × 96 ÷ 27	2.37
4 in slab plus turndown, ordered	7.11 + 2.37, rounded up	10.0

Two things fall out of that table and both belong in front of the customer. Going from 4 in to 5 in adds 25 percent to the material on an unchanged footprint, which is why the thickness decision gets made and written down before the order, not after. And the turndown that nobody can see once it is poured is a third of the ticket.

The rest of the takeoff comes off the same tape:

• Steel. #4 bar on an 18 in grid across 24 ft is about 16 bars each way, roughly 770 linear feet plus chairs and tie wire. Sheet mesh instead is 576 sq ft with laps. Say which on the invoice — they are not the same price and they are not the same slab.
• Base. 4 in of compacted aggregate under 576 sq ft is 7.1 cu yd loose, plus compaction in lifts. Bill the tonnage delivered and the compaction as its own item.
• Isolation joint. 96 linear feet of expansion material against the wall, plus a wrap at any post base.
• Saw cutting. The joint grid, in linear feet. More on that below.

Why is the access line the biggest surprise on a garage slab bill?

Because the walls were up when you poured, and a ready-mix chute reaches about sixteen feet from the back of a truck that has to stay on solid ground.

That single fact splits garage slabs into three price classes, and the invoice should name which one this job was.

Access condition	How the concrete moved	What the line costs you
Open slab, truck can back to the forms	Chute	Nothing beyond the mix
Framed walls, truck stops at the apron	Pump or conveyor, with a vendor minimum	A second vendor’s minimum hours, whether you use them or not
Finished structure, narrow door, soft yard	Power buggy or wheelbarrow	Crew hours, and a crew large enough to move ten yards inside the discharge window

Ten yards by wheelbarrow is roughly sixty round trips. That is not a rounding error on a labor line, and it is the number customers most often assume was included. If the access method changed between the estimate and the pour — the yard was wetter than expected, the neighbor’s car blocked the approach, the pump could not set up where you planned — that is a change order with a date on it, not a silent absorption.

Tear-out is the same story running backwards. Breaking an existing slab inside a standing garage means hand demo and a wheelbarrow through a three-foot service door, and the disposal is billed by the ton at the scale. Put the scale ticket weight on the invoice.

How do the joints, the slope, and the finish get written?

As three separate decisions with three separate consequences, because these are the lines that generate the callbacks.

Joints. Control joint spacing on a slab on grade generally runs 24 to 36 times the slab thickness, which puts a 4 in slab at 8 to 12 ft, and the cut should be at least a quarter of the slab depth — 1 in on a 4 in slab. The industry summary of that rule is NRMCA’s CIP 6 on joints in slabs on grade. On a 24 by 24 bay, quartering the slab gives 12 ft panels and 48 linear feet of cut; cutting it into thirds gives 8 ft panels and 96 linear feet. Bill the linear feet you actually cut and put the panel size on the paper, because the joint pattern is the thing the customer will point at when the first hairline appears — and a hairline inside a joint is the joint doing its job.

Slope. A garage floor drains toward the overhead door unless there is a drain in it. At 1/8 in per foot, a 24 ft bay falls 3 in from the back wall to the door, which is more drop than most homeowners picture, and many garages are built closer to 1/16 in per foot. Write the fall you built in inches, end to end. It is the cheapest way to end an argument about a workbench that sits crooked.

Finish. Steel trowel gives a dense, easy-to-sweep floor that is slick under a wet tire and a boot in February. A light broom gives grip and holds a little more dirt. That is a customer decision with a price attached, and the invoice should record which one they chose along with any hardener or densifier applied.

What changed between the estimate and the invoice?

On a garage slab, usually something underground, because you priced the job standing on grass.

What turned up	How it bills
Subgrade would not compact — soft spot, old fill, wet clay	Undercut and additional base, by the yard or ton, plus machine time
Old slab thicker or more heavily reinforced than expected	Demo hours plus additional disposal tonnage from the scale ticket
Thickness bumped from 4 in to 5 in for a lift or a truck	The 1.78 extra yards, plus the added finish time
Floor drain or conduit sleeve added on site	Each, itemized, with what it was sleeved for
Pump substituted for chute on pour morning	The pump vendor’s minimum, passed through at cost or at your stated rate
Cold morning start	Heated water, accelerator, and blankets as a named conditional line

Every one of those should already exist as a priced conditional on the estimate, so that using it on the day is a measurement rather than an announcement. Get the text approval before the truck is dispatched and screenshot it. Once ready-mix is on the road it cannot be sent back, and a change order argued at 7 a.m. with a loaded truck idling is an argument you will lose on price.

What gets handed over with the invoice on a garage slab?

Five things, and four of them are protection against a call in the spring.

• Photos of what got buried, in this order: compacted base, vapor barrier with taped seams, steel on chairs, and the turndown trench before the pour. This is the only proof that the invisible third of the invoice existed.
• The batch tickets, showing the yardage delivered and the specified psi and mix. Staple them to the bill. A customer who can read the ticket does not ask whether you shorted the order.
• The use schedule in plain sentences. Foot traffic in about 24 to 48 hours. A car in about a week. Full design load at 28 days, which is the age the specified strength is measured at. No loaded truck or dumpster on it before then.
• Two warnings that are specific to a garage and nowhere else. Keep deicing salt off it through the first winter — a car parked wet drips brine straight onto a slab that has not finished gaining strength. And no epoxy, no coating, no sealer until the slab has cured out and passed whatever moisture test the coating manufacturer requires, which is generally at least 28 days. Customers buy the coating kit the week you leave. Write it down.
• The joint map and the finish you applied, so the next contractor in that building knows what is under him.

How do I get paid before the compactor goes on the trailer?

By doing the walkthrough with the door open and the slab still dark, which is the two-hour window when the work looks exactly as good as it is.

Walk it once. Point at the yardage on the batch ticket, the joint pattern you cut, the fall toward the door, and the two change orders in the order they happened. Then hand the invoice over on your phone with the payment link rendered as a QR code and take the balance standing on the apron. A garage slab balance is a card tap. Sent home in an envelope, it becomes a conversation about a hairline in three weeks. If it does go unpaid, the sequence to run is in how to get clients to pay, and it works far better started on day two than on day forty.

What you hand back after the payment clears is a receipt, not another invoice, and the difference matters more than it sounds — see invoice vs receipt. A driveway pour in the same yard bills on its own rhythm, laid out in how to invoice after driveway concrete.

How do I know the number I invoiced fast is the right number?

Build it from your own costs, not from a per-square-foot figure somebody posted for a different climate.

Start with the units that match what actually drives cost: slab surface by the square foot, turndown and footing volume by the cubic yard, forms and isolation joint by the linear foot, saw cutting by the linear foot, steel by weight or by sheet, base by the ton, disposal by the ton, and pump or buggy by the vendor’s minimum. Then load your crew hour honestly — wages plus payroll burden, comp, liability, truck and trailer, mixer, power trowel, saw and blades, and the unbilled hours spent staking, quoting, and waiting on an inspector. Divide by the hours you actually sell, not the hours you work.

Then take profit as a margin, not a markup, because on a job where material and vendor minimums can be half the ticket, the gap is not academic. Add 30 percent to $7,000 of cost and you bill $9,100 and keep 23 percent of it. To keep 30 percent you divide by 0.70 and bill $10,000. Markup multiplies, margin divides. Published per-square-foot prices swing hard by region, psi, access, finish, and season, so use them only to notice you are off by half — your own cost is the number that decides.

What stays in the file after the joints are cut?

The takeoff with both yardages, the batch tickets, the pump or buggy cost, the steel and base receipts, the scale tickets from demo, the pre-pour photos, the change-order texts, the invoice, and the receipt you handed back.

Keel is built for the version of that where you are standing on an apron with wet boots and one bar of signal. It is an iOS app that runs entirely on the device — no account, no bank connection, no cloud, no login, and an App Store privacy label reading Data Not Collected — so the invoice gets made where the slab is rather than at a kitchen table on Sunday night. It carries your own numbering series, your logo, your brand color, and line items at whatever unit the scope used: square feet for the slab, cubic yards for the turndown, linear feet for the saw cut, each for the sleeves. The payment link renders as a QR code the customer scans on the spot. Batch tickets, the pump invoice, and the scale ticket get photographed at the truck and read on device by Apple Intelligence, so the yardage you were billed for stays attached to the slab it went into. Plant and yard runs log as mileage. Freeboard shows cash minus tax reserve minus committed invoices minus buffer, which on a trade that pays the plant before the customer pays you is the only number that answers whether next week’s pour is funded. The ledger is append-only and hash-chained, and the year exports as a single file or as the Accountant Pack of CSV plus a one-page summary PDF. Free is $0 with unlimited invoices, receipts, and mileage. Keel Pro is a one-time $249.99 Lifetime purchase, not a subscription.

Frequently asked questions

How do I calculate how many yards a garage slab needs?

Square feet times thickness in feet divided by 27, and for a 4 in slab the shortcut is square feet ÷ 81. A 24 by 24 bay is 576 sq ft, so 7.11 cu yd. Then add the turndown separately: 12 in wide by 8 in below the slab around 96 linear feet is another 2.37 cu yd, so you order 10.

Should a garage slab be 4 inches or 5 inches thick?

That depends on what parks on it, and it needs deciding before the order because 5 in is 25 percent more concrete on the same footprint — 8.89 cu yd instead of 7.11 on a 24 by 24. Passenger cars sit fine on a well-based 4 in slab. A loaded truck, a hoist, or a lift is a thickness and reinforcement conversation, in writing.

How far apart should control joints be in a garage floor?

Common guidance is 24 to 36 times the slab thickness, so 8 to 12 feet on a 4 in slab, cut at least a quarter of the depth. On a 24 by 24 bay that is either four 12 ft panels with 48 linear feet of cut, or nine 8 ft panels with 96. Put the panel size on the invoice so the first hairline is a joint working, not a defect.

Do I charge extra for pumping concrete into a finished garage?

Yes, as its own line, because it is a second vendor with its own minimum hours that you pay whether or not you use them. If the walls were up when you poured, a chute does not reach and the concrete moved by pump, conveyor, or buggy. Ten yards by wheelbarrow is roughly sixty round trips and it belongs on the labor line, itemized.

When can the customer park on a new garage slab?

Foot traffic in about 24 to 48 hours, a passenger car in about a week, and full design load at 28 days, which is the age the specified strength is measured at. Print that on the invoice along with two garage-specific warnings: no deicing salt through the first winter, and no epoxy or coating until the slab has cured and passed the coating maker’s moisture test.

What proof should I give the customer that the base and steel were right?

Photos taken in sequence before the pour — compacted base, vapor barrier with taped seams, steel on chairs, and the turndown trench — plus the batch tickets showing yardage and specified psi. A third of a garage slab invoice is work that is invisible ten minutes after it is finished, and those photos are the only record that it happened.

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This article is general information, not professional or tax advice.