Worked case: a 700 sq ft three-car polyaspartic flake garage on an older hillside slab on the Highland slope — what happens and what it costs

The scenario

Picture a hillside house in Hayward Highland built in the 1960s, with a three-car garage under the main floor and a driveway that drops toward the street. The slab is roughly sixty years old, 700 square feet, with a patchwork of hairline cracks, a few chipped corners at the door, old oil stains under two bays and a faint chalky film where the concrete has dusted. The doors face open sky for much of the day, and the owner uses the garage as a workshop on weekends.

The older slab was poured when vapor barriers were far less common, and the lot is on a hillside, so moisture is a live question. The brief is a durable floor that takes sun at the open doors and goes back into service quickly, so the owner picked polyaspartic flake.

The starting conditions at a glance:

• Area: about 700 sq ft, three bays
• Slab: older, with hairline cracks and chipped corners
• Moisture: unknown; a test is needed before anything goes down
• Setting: hillside, doors facing sky, a sloping apron
• Use: parking plus weekend workshop

What the job involves

1. The installer walks the slab with chalk and marks every crack, chipped corner and soft spot, and taps the floor to find any hollow-sounding patches.
2. A calcium chloride test and an in-slab humidity probe are used on the largest bay and the downhill bay; readings guide whether a moisture-mitigating primer is specified.
3. A diamond grinder opens the whole surface, oil-stained areas are ground a second time and the dust is collected through a vacuum; chalky concrete is ground back to sound material.
4. Cracks are routed and filled with a repair product and ground flush; chipped corners are filled with a patching mortar and allowed to cure.
5. The moisture-mitigating primer goes on the whole floor, followed by a polyaspartic base coat, a hand-thrown full flake broadcast and a polyaspartic topcoat in the same visit.
6. The garage doors stay open for ventilation, the floor cures for the time on the data sheet, and the owner is told when foot traffic and vehicles can return.

Materials and prep

• Diamond grinder with shroud, hand grinder, HEPA-style vacuum and a moisture-test kit
• Crack-routing tool, repair filler and a patching mortar for chipped corners
• Moisture-mitigating primer rated for the measured readings
• Polyaspartic base coat, full-broadcast flake and a polyaspartic topcoat
• Squeegees, notched trowel, rollers and spiked shoes
• Ventilation fans, masking and plastic drop sheets for the house door

Add-ons often paired with this job

• Extra joint and crack repair beyond the usual — +$100–$300. An old hillside slab usually earns an extra crack-repair line beyond the usual, with every crack routed and filled.
• Moisture-vapor barrier primer over the whole floor — +$350–$900. A primer over the whole floor is a flat line when the moisture readings call for it.
• Coat the stem wall or garage-door curb — +$150–$350. A low wall between the garage and the house can be coated for a finished edge.

Why it is done this way

Polyaspartic flake is the right fit for three reasons. The doors face open sky, and aliphatic polyaspartic topcoats are generally more UV-stable than epoxy, which can amber in sunlight. The owner wants the garage back in use quickly, and many polyaspartic systems install in one day. And the floor is large, so a system that sets fast limits the time the doors stay open to the weather.

The preparation carries more weight than the product. An older slab on a hillside needs its cracks mapped, its moisture read and its surface ground. A polyaspartic coat sets so quickly that a missed hollow spot or a damp reading cannot be fixed afterwards.

The alternatives that were weighed and set aside:

• Epoxy flake with a polyurethane topcoat costs $6–$10 per square foot and would suit a covered garage; here the sun and the quick return favored polyaspartic.
• Skipping the moisture primer saves money but risks a coating that lifts from below on a damp slab.

What would change the price

• Moisture readings come back higher than expected — the primer specification gets heavier or the job is reconsidered.
• A crack proves to be wider and still moving — a concrete trade is called in first.
• Old floor paint or mastic from before the late 1970s tests positive for lead or asbestos — a more careful removal plan follows.
• The apron slopes into the garage so water runs under the door — a threshold detail is added.
• The owner wants the floor back in use by a set day — the schedule narrows the weather windows.