The Traverse City station record
NOAA publishes engineering weather data for a station in Traverse City, at an elevation of 623 feet. For Traverse City, that record gives:
- a 1% summer design temperature of 86°F, with a mean coincident wet-bulb temperature of 70°F;
- a 99% winter design temperature of 2°F;
- in an average year, about 103 hours with the wet-bulb temperature above 73°F and about 576 hours above 67°F;
- a 50-year basic wind speed of 90 mph, given as a 3-second gust at 33 feet;
- a 100-year rainfall rate of 2.5 inches per hour;
- about 66 freeze-thaw cycles in an average year.
Those six lines are the station's published figures for Traverse City. They describe the station, not the particular patch of ground behind your garage.
A separate local fact: the city's drinking water
Traverse City draws its drinking water from Lake Michigan. The intake is a steel-and-wood crib about 15 feet across, lying about 40 feet below the surface, and a low-service pump station sends raw water from it to the filtration plant. That is a fact about the tap water supply only.
Match the slab to its load
Concrete work goes smoother when the homeowner can describe the job in a sentence or two per surface. For each area, jot down:
- what it is: a driveway, a garage floor, a patio, a walk, a set of steps, a pad for a shed or a hot tub;
- what rolls or sits on it, from bare feet to a pickup towing a boat trailer;
- rough dimensions, and whether the shape is a plain rectangle or has curves;
- the finish you want: broom texture, smooth trowel, stamped pattern, exposed aggregate or a color;
- what is there now and has to come out, if anything.
Hand the same sheet to every company you call. A driveway that carries a loaded trailer needs a different thickness than a garden path, and you want each bidder pricing the same thing.
Digging and the base underneath
A slab rests on whatever the crew leaves under it. Topsoil, roots and loose fill compress and rot over time, and the concrete above them sinks or cracks. Ask each company:
- How deep will you excavate, and what do you do if you hit soft, wet or organic soil?
- What base stone goes in, how thick, and is it compacted in layers with a plate or roller?
- Do you extend the base past the edge of the slab so the edges are supported?
- Who calls in the utility locate before digging, and what happens near a water service, gas line or sprinkler pipe?
Mix and steel
Ask what strength the concrete is ordered at and whether outdoor flatwork will be air-entrained. Entrained air leaves tiny bubbles in the paste that give freezing water room to expand. Ask what the crew does if the mix arrives stiff: adding water at the truck makes concrete easier to place and weaker once it hardens, while a plasticizer added at the plant does not carry that penalty.
Reinforcement differs by job. Rebar, welded wire and synthetic fibers each serve a purpose, and steel that ends up lying on the base adds very little. Ask what your slab gets and how the crew keeps it in the middle of the slab's depth while the concrete goes in.
Joints, planned in advance
Every slab shrinks as it dries, so cracking somewhere is expected. Control joints give that crack a straight, tidy place to happen. Ask for the joint layout on paper, with spacing and depth, and whether the joints will be tooled while the concrete is wet or sawn within the first day. Where new concrete meets the house, a step, a garage apron or an older slab, ask whether an isolation strip will separate them so each can move on its own.
Sending water off the surface
Ask how much slope each surface gets per foot and which direction it falls. A patio should shed water away from the house; a driveway may need to drain toward the street or to one side. Ask whether downspouts that now empty onto the area will be extended or piped before the pour, and how the soil along the slab edge will be graded so water runs off instead of soaking under.
Pour day and curing
Ask what weather would make the contractor postpone, whether for heat, cold, wind or rain, and how much notice you will get. Ask how the fresh slab will be cured: wet coverings, plastic sheeting, a curing compound, or a combination, and for how many days. Ask how it will be protected if a cold night comes in the first week, and when you can walk on it and park on it. Ask which sealer the company recommends, when the first coat should go down, and which deicers to avoid on new concrete.
Paperwork to settle early
- What state license, if any, covers this work, and what is the number?
- Which city permits does this job need, and who pulls them?
- Is an inspection part of the job, and at what stage?
- Can you show proof of liability coverage and workers' compensation?
Putting the bids side by side
Lay out the written bids and check each one for:
- square footage, thickness and finish for every area;
- removal and disposal of old material;
- excavation depth, base material and compaction;
- mix strength, air entrainment and reinforcement;
- the joint layout and the slope plan, including downspout work;
- the curing method and any sealer;
- permits, utility locates and cleanup;
- the written warranty and what it excludes.
A bid far below the others may have left something out. Find the missing line and ask about it before you sign.