What skipping one sealcoat cycle really costs a parking lot

A property manager asked me to put a number on what it had cost to skip the last sealcoat. The lot had been sealed on a three-year cycle for a decade, then a new owner, a new budget, and the cycle was missed. Five years on, the lot needed patching across a third of it and an overlay over all of it. Here is the arithmetic, in round numbers, so that the next board can see the shape of it before the vote.

What sealer does, and what it costs

Sealcoat is a thin film of coal-tar or asphalt emulsion with sand in it. It keeps the sun off the binder in the asphalt, which is what turns a black lot gray and brittle, and it keeps water out of the surface, which is what turns hairlines into cracks and cracks into potholes. It does not fix anything; it preserves what is there. Applied every two to four years, with the cracks filled every autumn, it is priced by the square foot and is the cheapest thing you can do to pavement. For this exercise call a seal-and-stripe a unit of one.

The lot that is kept

Take a 40,000-square-foot lot, about 110 stalls, kept on a three-year cycle. Over fifteen years it is sealed five times and crack-filled fifteen times. The asphalt underneath stays black and flexible; the cracks stay small; the potholes are the plow's doing and are patched the spring they appear. At year fifteen the lot is at what I call stage one in the stage article: gray between seals, sound underneath, and good for another fifteen with the same program. Total spend over fifteen years: five units of sealing plus the annual crack-fill, call it six or seven units.

The lot that is not

Same lot, the cycle stopped at year nine. Year ten: the surface goes gray and the hairlines open. Year eleven: the open cracks take the winter's water into the base, and in spring there are a dozen potholes and the first alligator patches where the trucks turn. Year twelve: the alligator patches have spread; the drive lanes are rutting. Year thirteen: the lot is at stage three, and the honest repair is to cut out and rebuild the failed areas and overlay the rest. An overlay with patching, by the square foot, costs on the order of ten to fifteen units; reconstruction of the failed third, more. And then the new surface needs sealing in a year, which starts the cycle the owner stopped.

So the choice at year nine was: spend one unit now and one every three years, or spend nothing for four years and then spend twelve. The "savings" from skipping two seals, two units, bought a bill six times larger. The FHWA's rule of thumb for pavement preservation is that a dollar spent early saves several spent later, and on a parking lot in a Cleveland winter the several is not an exaggeration.

Where the money actually goes

The expensive part of a failed lot is never the surface. It is the base: the stone under the asphalt that water has washed fines out of through the open cracks, so that it no longer supports the pavement and has to be dug out and replaced before anything is paved on it. Sealer keeps the water out of the surface; crack filling keeps it out of the base. Skip both and the water does its work for years before anything shows on top.

When sealing is the wrong spend

The same arithmetic says not to seal a lot that is already at stage three. Sealer over alligatored asphalt lasts one winter and hides the problem from the people who should be budgeting for it. If the lot has got away, patch and overlay it, then start the cycle on the new surface. We tell owners this on the walk even when they called for a seal, because a seal on a failed lot is a bill that buys nothing.

The board's version

• Seal every two to four years, fill cracks every autumn, restripe with each seal.
• Budget the seal as a line item on a cycle, not a project to be approved each time.
• Have the lot walked each spring and each autumn, and photographed.
• If a cycle is missed, do not miss two; the second one is the expensive one.
• If the lot is already past sealing, overlay it and start again; do not seal it.