Why do people fill the cracks of paved parking lots with tar or oil filler?

Answer 1

You'll see it on roadways, as well. It's an oil-based sealant designed specifically for that purpose.

Before asphalt is laid down, they basically grade out a bed for it, and often have to add a road base if the bare earth is inadequate for a base. The base could be crushed concrete, ABC mix, processed fill, etc.

Asphalt is basically oil, sand, an aggregates (stone). Some mixes might add mineral fill, lime fill, fiber, etc, but, at it's core, it's oil, sand, and stone.

As cracks develop in the asphalt, it has a couple effects. For one, water can get in there, freeze, and then thaw. This causes expansion and contraction, which aggravates the cracking in the asphalt.

The other effect it has is to allow water to flow through the asphalt to the base, and wash out the base. This leaves the asphalt unsupported, and it eventually caves in.

Crack sealant is intended to prevent water intrusion into these cracks, for the sake of preventing the two scenarios described above.

It is typically done prior to having seal coating, chip seal, or slurry done on roadways.

There are two types of crack sealant.. one type is just an oil mixture, and is intended for cracks less than an inch in width. This is squirted out of a trailer or vessel designed for this purpose.. usually a trailer, and fully self contained. One person will squirt the tar with the wand, and the other workers will use squeegees to spread it along the length of the crack (and also keep it from spreading out too far).

The other type, intended for wider cracks, also has aggregate mixed in, and is dumped from the back of a trailer, rather than squirted out through a wand (the ag would destroy the pump if you tried to spray it from the type of tar pot used for the first type of crack fill). Specifics of this kind, I'm not certain of, as I've never worked with it personally.