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Setting Forms and Grade Stakes for a Driveway

By concrete contractor carlsbad notes

Forms are the mold

Wet concrete has no shape of its own. It takes the shape of whatever holds it, and for flatwork that means forms: straight boards, metal strips or flexible sheets set along the edges of the slab. Because the forms define the width, the edge line, the finished height and much of the slope, a driveway that is formed carefully looks right, drains right and fits the garage right. A driveway formed in a hurry looks like it.

Grade stakes and the finished height

Before any board is set, the crew drives grade stakes, short wooden or steel pegs, at intervals around the perimeter and sometimes through the middle. Each stake is marked with the height of the finished concrete, either with a line drawn on it or a measured offset. The marks come from a reference point such as the garage threshold or the street curb, which is why those two heights are fixed first.

Setting the marks takes a level, a laser or a transit and a measuring rod. The crew sights from the reference point to each stake and records the difference. If the slab is meant to fall a certain amount over the length, the marks step down in even increments. When the marks are all connected by a string line, the line forms the plane of the finished surface, and a glance reveals any section that sags or humps.

Choosing form material

Lumber works well for straight runs. Two by four boards are common for thinner slabs, with taller boards for thicker ones, and the boards are selected for straightness since a bowed board produces a bowed edge. Steel forms are reusable, rigid and available in lengths that suit long runs. For curves, crews use thin, flexible material, such as bendable plastic or thin hardboard, held in the arc by stakes set close together.

Whatever the material, the top of the form is the guide for screeding, so it has to be at the finished height, and the inside face has to be clean and straight. Oil or a release agent is often applied to make removal easier and to keep the edge from sticking.

Staking and bracing

Wet concrete is heavy and pushes outward on the forms. Stakes driven outside the boards at regular intervals hold them in position, and nails or screws attach the boards to the stakes. Spacing is closer on curves and at corners, where the pressure is greatest. Extra bracing at joints between boards stops them from shifting out of line.

A stake that wobbles in loose soil will not do its job. Crews drive stakes deeper in soft areas or add bracing blocks, and they check the forms again after the first few loads, since weight can move a form that looked solid.

Checking line and level

With the forms set, the crew verifies two things: line, which is how straight or smoothly curved the edge is, and level or grade, which is the height and slope. A string pulled along the top of the forms reveals dips and bumps. A level or laser confirms the slope. Where the form is off, a few taps with a hammer or a shim under a board corrects it.

The slope toward drainage should be confirmed at this stage with a simple test: lay a level on a straight board across the forms, with a small block under one end sized to the intended fall. If the bubble sits where it should, the pitch is right. Any mistakes caught here cost minutes. Caught after the pour, they cost a demolition.

Where the forms meet existing concrete

At the garage, the sidewalk and the street, the new slab has to meet something that already has a height. The forms there are set to match, with allowances for isolation joint filler, which takes up space between old and new. If the filler strip is a half inch thick, the form is moved over by that amount. Matching heights carefully prevents a lip that trips a visitor or catches a mower wheel.

At the street end, the apron may be controlled by the city, with specific dimensions and heights for how the driveway meets the gutter. The crew should know what is required and set the forms accordingly.

Pins, dowels and things that must go through the forms

Sometimes the plan calls for steel dowels, bars that cross from one slab into another to keep them aligned. They poke through holes drilled in the forms, so that half of each dowel ends up in each pour. Sleeves for irrigation or conduit are also placed before the pour and marked at the surface so no one forgets where they are. A forgotten sleeve is not a disaster, but a sleeve nobody can find years later is a nuisance.

What a homeowner can check

• Forms sit snug against the stakes with no visible gaps.
• The top edge is clean and follows the string line.
• Curves are smooth, not a series of straight segments.
• Grade marks match the plan at the garage and the curb.
• Bracing is solid, and the stakes do not move when pushed.

Photographs of the forms are useful records, and it takes a moment to take them. They show later where the edges sit, how thick the slab was meant to be and where any embedded items lie. A pause of ten minutes to inspect the forms before the truck arrives is not an insult to the crew. Good crews expect it and often welcome it.

Mistakes that forms reveal

Several defects can be traced straight back to the forming stage. A wavy edge means the boards were not straight or the stakes were spaced too far apart. A slab that is thin at one end means the grade marks were read wrong or the base was uneven. A step at the garage means the threshold height was not checked against the form. A puddle near the middle usually means two grade marks were set carelessly and the string line was never pulled tight across them.

Another quiet mistake is leaving forms resting on loose soil that has not been tamped. Under the weight of workers and wet concrete, the board sinks a fraction of an inch, and that fraction becomes a dip in the finished edge. Tamping the ground beneath each form, or setting it on a firm shelf of undisturbed soil, solves the problem.

Removing the forms

Forms stay in place until the concrete has hardened enough to hold its edge, usually the next day or later depending on the weather. Pulling them too early can chip the edges. The crew then backfills along the slab with soil to support the edge and restore the yard, taking care to slope the soil away so water does not collect against the concrete.

Stakes and boards are hauled away, leaving a clean, straight edge as the record of work done before the pour began.