Reading a Concrete Bid Line by Line

My wife still calls it “the summer of the patio.” I poured a 12 by 16 slab behind our house in Colorado Springs myself, saved maybe $1,800, and spent three weekends and a good amount of skin off my knees getting there. The slab is fine. It also has a low spot by the back door that holds a puddle for two days after a storm, and I look at it every August.

The useful part came later. When the driveway had to go, three bids landed in my inbox and I could read them, because nearly every line was something I had paid for at a rental counter or hauled in my own truck. That is my only credential. I am not in the trade; I just know what each step costs when an amateur does it.

The concrete itself is the cheapest thing on the page

This surprised me most. Ready-mix delivered runs roughly $150 to $240 per cubic yard. A 600 square foot driveway at 5 inches thick is about 9.3 yards, call it 10 with waste — $1,500 to $2,400 of actual concrete inside a bid that might total $9,000.

For the patio I mixed bags, because no truck fit down the side yard. A cubic yard is roughly 45 of the 80 pound bags, so at $6 to $8 each that is $270 to $360 per yard — near double what the truck charges, for four times the work. Plants also carry a minimum load of 8 to 10 yards and bill $40 to $75 per yard under it, which is why a small pour never prices out the way you expect. The ready-mix trade group, NRMCA, publishes the basics, and I wish I had read them in April rather than in August with a wheelbarrow in my hands.

Most of a bid is dirt, forms and hours

Here is what the rest of the lines represent, with the rental prices I paid:

Demolition and haul-off, $2 to $6 per square foot. A 600 square foot, 4 inch slab weighs close to 15 tons, and a dumpster runs $450 to $800. Nobody warned me about the dirt pile either: digging that area down 8 inches makes 15 cubic yards of spoil.
Base, $1 to $3 per square foot. Four to six inches of compacted road base. A vibratory plate compactor rents for $70 to $110 a day, a jumping jack for clay $95 to $150. Forms and stakes were another $180 to $400.
Placing and finishing labor. The big number, and the one you cannot rent your way out of. A truck gives you roughly 45 minutes to place a load once it starts discharging, and that clock is why I no longer think most people should pour their own driveway.
Saw cutting joints. A walk-behind saw is $95 to $160 a day plus a blade, and the cuts happen 6 to 18 hours after the pour.

The numbers I make a bidder write down

A bid that says “concrete driveway, broom finish, $8,400” cannot be compared to anything. I ask everyone for the same items in writing, and the spread usually shrinks to fifteen percent once they are all quoting the same thing:

Thickness in inches. Four for cars, five or six if a delivery truck, RV or dumpster will ever sit on it.
Strength in psi. 3,500 minimum, 4,000 to 4,500 anywhere that freezes, plus 5 to 7 percent entrained air in a cold climate.
Reinforcement. Fiber, welded wire, or #4 rebar at 18 inches on center — and whether the steel is held at mid-depth or dropped on the dirt. Steel lying on the ground does nothing.
Base depth and compaction. Material, inches, and a target such as 95 percent Proctor.
Curing method. Our June air is dry enough that a slab loses surface water as fast as you can finish it. Seven days under wet burlap is the cheapest strength you will ever buy.

Exclusions are where the surprises live

That page is short and it is the expensive part. Watch for permits and the apron in the public right of way, which is city-regulated work with its own inspection; dirt haul-off listed as “by owner”; allowances instead of fixed prices on base rock; and the unforeseen subgrade clause. That last one is not a scam. We sit on bentonite clay that swells and shrinks with moisture, and if a crew digs out and finds two feet of soft wet clay, somebody has to pay for it. For a cleaner way to line three bids up, see getting comparable quotes from concrete contractors.

Frequently asked questions

Is the cheapest bid always the worst one? Not always, but it is usually the smallest scope. My low bid was 4 inches with fiber and no base rock; the high was 5 inches with rebar over 6 inches of compacted base — about $3,100 apart. Asked to price the same section, the low bidder landed within a few hundred dollars of the others.

How much does doing it yourself really save? On a small patio, maybe $6 to $9 per square foot. On a driveway, less than you would think: rentals, bag concrete, dumpster fees and a second set of hands eat the margin, and one mistake inside those 45 minutes costs more than the savings.

Should I pay a deposit? A deposit for materials is normal; a large payment before anything is on site is not. I paid a third at start, a third at pour, the balance after the joints were cut — and that schedule was on the bid before I signed. Historic work runs on the same schedule of milestones — a Washington DC masonry contractor ties payments to staging up, repointing complete, and final cleanup.

Industry reference: Portland Cement Association.