Why Do Epoxy Floors Peel in Bloomington? Karst Moisture, Road Salt and Skipped Prep

September 9, 2026

Most peeling floors in Monroe County were doomed before the first coat went down, and the cause is almost always one of four things that a written scope should have named.

The ground under the slab is never dry

Bloomington sits on the Mitchell Plateau, the karst belt that INDOT describes as running from eastern Owen County south to the Ohio River. Karst means limestone that dissolves in slightly acidic rainwater, so drainage goes underground through sinkholes and conduits, the water table sits shallow, and surface water moves underground rapidly. The city's stormwater page says it plainly: Bloomington and the surrounding area contain karst. The rock itself, the Salem Limestone, is a porous calcarenite 60 to 100 feet thick in the outcrop belt, the same stone the building trade sells as Indiana Limestone.

For a slab that means a continuous supply of moisture from below, which the site's limestone-country concrete guide explains in detail. Pre-war slabs in Prospect Hill and McDoel Gardens were poured without a vapor barrier, and even a 1990s slab on gravel and plastic sits in a county that averages 49.38 inches of precipitation a year, with April through June each above 5.2 inches.

Moisture vapor: the failure nobody can see

Water leaves a slab as vapor until something traps it. A coating traps it, and the pressure under the film lifts it in blisters and sheets, usually the first spring. Two ASTM tests measure the risk first. ASTM F1869 seals an anhydrous calcium chloride dish to the floor and reports pounds of moisture emitted per 1,000 square feet in 24 hours; ASTM F2170 drills a probe into the slab and reads the relative humidity inside the concrete.

The limits in published specifications are specific: one resinous flooring guide specification caps emission at 3 pounds per 1,000 square feet per 24 hours and internal relative humidity at 75 percent, and a 100 percent solids epoxy data sheet uses the same 3 pound and 75 percent lines. Readings above those numbers do not rule out a floor. They move the scope to a moisture-mitigating primer, or to drainage work first, and white efflorescence is the visual flag that the test is needed.

Road salt, brine and the freeze-thaw cycle

INDOT keeps more than 1,000 plows and 29,000 lane miles in its winter program from mid-November to mid-March, and it pretreats roads with a brine of 23.3 percent salt that stays active down to about 20 degrees F. Every trip up State Road 37 or Interstate 69 brings that brine home on the tires, where it drips onto the slab and dries into crystals. On bare concrete the salt drives the freeze-thaw cycle that the ready-mix industry calls scaling: local flaking or peeling of the finished surface, which is why the NRMCA tells owners not to use calcium or sodium chloride deicers at all in a slab's first year.

January in Bloomington averages 26.1 nights at or below freezing, so a wet, salted slab crosses the freeze line most nights all winter. A bare garage floor loses its surface a flake at a time; a floor coated over a scaling surface loses both, because the film is only as strong as the concrete it grips.

Acid etching and other prep shortcuts

The second most common failure is bond, and bond is decided by profile. ICRI Technical Guideline 310.2R, updated in 2013, defines concrete surface profiles CSP 1 through CSP 10 and summarizes what each preparation method can and cannot deliver. Published epoxy specifications ask for CSP 2 to 5, or CSP 3 to 4 by shot blast, and a diamond grinder reaches the light end of that scale on a sound slab. Acid etching, the method in most kit instructions, does not reach it reliably on the machine-troweled caps of newer local slabs, ignores curing compounds entirely, and one data sheet prohibits muriatic acid outright because of chloride contamination.

Laitance, an old sealer, a curing compound from the pour, or a surviving layer of paint are the other bond killers, and none of them washes off. That is the case for concrete grinding and surface prep as a line item on every scope, checked with a water-drop test before the primer opens.

Hot tires, thin paint and the wrong product

The third failure belongs to the product. Hardware-store garage paint is a thin film, and a thin film over an unground slab has two enemies here: a July high of 85.1 degrees F that lets a hot tire soften the film and peel it on the next cold start, and the salt described above. Some epoxies also chalk and yellow under the sun that comes through an open door on a Whitehall Pike garage, while published polyaspartic data sheets are UV stable and rated not to yellow.

A garage floor coating built as a system, meaning a primer matched to the moisture reading, a high-build body coat and a UV-stable topcoat, avoids all three failures. It also has to be applied inside its weather window, which in this climate is a scheduling decision as much as a product one.

What a floor that lasts looks like on paper

Peeling is rarely a mystery once the scope is read back. Garage and basement floor coatings across Bloomington hold up when the written scope includes these lines:

• A moisture test by ASTM F1869 or F2170, with the reading and the product limit written next to each other
• Mechanical grinding or shot blasting to a named CSP profile, never acid etching alone
• Removal of every old coating, sealer and curing compound, verified with water absorption across the whole floor
• A primer chosen from the moisture reading, mitigating where the number calls for it
• Application dates that keep the slab inside the data sheet's temperature and dew point limits
• A UV-stable topcoat where daylight reaches the floor

More from the blog

• Coating an Auto Shop Floor in Bloomington: Oil, Brake Fluid and Winter Brine
• Fall Booking Guide: Why September and October Fill First in Bloomington
• New Concrete in Bloomington: the 28-Day Rule Before Epoxy