How a String Line Shows Driveway Grade

A tight string from the high point to the low point shows dips and humps the eye misses. If the string touches in the middle, that spot is high. If you see daylight under it, the spot is low. Grade the base to the string before the asphalt arrives.

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What the string is showing you

Stand at the garage and the street and the driveway can look flat while it hides a hump and a birdbath. Pull a tight string from the high point you want to the low point you want, and the string becomes a straight reference. If the string touches the base in the middle, that spot is high and will telegraph into the asphalt. If you see daylight between the string and the stone, that spot is low and will hold water unless you fill it. The eye forgives a long sag. The string does not. Do this on the gravel base before the plant is called. Asphalt follows the base. A paver cannot invent a straight grade that the stone does not already have.

How to keep the string honest

A string is not a laser. On a long lane it sags under its own weight, and a sagging string makes a true grade look low. Check a long drive in segments short enough that the line stays tight, and pull it hard. Set the ends at the elevations you mean, not at random stakes in the grass. Measure down from the string to the base at several stations and write the gaps. A consistent gap means the base is parallel to the string. A gap that shrinks to zero is a high spot. A gap that grows is a dip. For cross slope, run a second string across the width. One line down the center will miss a tilt toward the flower bed.

What to fix before the truck comes

Knock down highs and fill lows with the same compacted stone you are using for the base, in thin lifts a plate or roller can actually pack. A loose pile under the string looks filled until the paver rolls over it. If the dip is a soft pocket, dig it out instead of burying mud. The asphalt order still uses the area and the thickness: length times width times inches over 12, times 145 pounds per cubic foot, divided by 2000. That is a planning estimate, and the plant ticket is the real weight. Extra stone to fix grade is a quarry ticket, often planned near 1.4 tons per cubic yard, also an estimate until the quarry weighs it. Do not pave a base that the string says is wavy and hope the screed will average it out.

A practical sequence

Pull a tight string from the high point you want to the low point.
Mark where the string touches as high and where daylight shows as low.
Check long lanes in short segments so sag in the string does not fool you.
Grade and compact the base to the string before asphalt is ordered.

The mistake to skip

Trusting one sagging string down a long lane and paving the wavy base anyway.

Questions people ask

Can the paver smooth a base the string says is uneven?

The screed bridges small texture. It does not erase a hump or a birdbath you can see under a string. Those shapes come through the mat, and a thin overlay makes them more obvious. Fix the stone first. If you are overlaying old asphalt, a leveling course can fill small lows, but a string that shows a deep sag means more tons than a uniform thickness.

Do I need a laser instead?

A laser or a survey level is better on a long lane, a parking lot, or anywhere elevations tie to a curb or a building. A string is enough to find highs and lows on a short driveway if you keep it tight and check in segments. Use the tool that matches the length. Either way, grade the base before the hot mix shows up.

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