What to Ask a Garage Floor Coating Contractor Before You Sign
September 8, 2026
Two bids for the same garage can describe two completely different floors. Six questions surface the difference before any money moves.
Why September Is When These Questions Matter
Quote season on Long Island runs hottest in September and October because the standard-epoxy calendar has a floor under it: the slab needs to hold roughly 55F and rising for most epoxies to cure properly, and by January the Islip normals sit at 39.2F for a high and 24.6F overnight. An unheated garage bay stops being install-friendly well before the calendar says winter. The bids collected this month decide whose floor gets done before the season closes.
The problem is that two bids for the same two-car garage can describe two entirely different products - a thin film rolled over a lightly cleaned slab, or a ground, tested, twenty-plus-mil system - and the paperwork rarely says which. The published ranges on the cost guide show how wide honest pricing runs; the questions below force each bid to declare what it actually is. Put the same list to an epoxy flooring company in Smithtown and to whoever else is bidding the job. The answers sort the field faster than the prices do.
How Exactly Will You Prep the Slab?
The answer to listen for is mechanical: diamond grinding to a measured profile. ICRI Technical Guideline 310.2R-2013 defines concrete surface profiles from CSP 1 through 10, and thin-film coatings are specified at the low end of that scale - an installer who can name the target profile has read the spec, not just the label. An answer built on acid etching alone, or on cleaning products, is how a machine-troweled garage slab ends up shedding its coating in sheets. Grinding and surface prep covers what the process involves; the follow-up question is how edges, corners and the apron transition get profiled, and what happens to the dust.
Which Moisture Test, and What Number Fails?
A flashlight sweep is not a moisture test. Three real ones exist, in ascending order of information: a taped plastic sheet per ASTM D4263, which only screens for a problem; a calcium chloride test per ASTM F1869, which reports vapor emission in pounds per 1,000 square feet; and in-slab probes per ASTM F2170, which read relative humidity inside the concrete. Common coating limits sit near 3 to 5 pounds per 1,000 square feet, or 75 to 80 percent internal RH. Ask which test the bid includes and what number triggers a change of plan.
That last part matters most. If the slab fails the test, the honest path is a mitigation primer specified under ASTM F3010, priced before signing rather than discovered as a change order. An older slab may have no vapor retarder under it at all - the modern spec under a new pour is an ASTM E1745 Class A sheet - and the ground conditions that shape local slabs are laid out on the slab and climate data page.
What Goes Down, and How Many Mils?
Epoxy is a chemistry, not a thickness, and thickness is the wear budget. Ask for the build in mils per coat, in writing - then ask which primer, which topcoat chemistry, and the recoat window between coats. A bid for a real garage floor epoxy system names all of it without a callback. The spread that one mil number covers:
- 3-5 mils: the film a big-box kit leaves behind
- 15-25 mils: a residential two-coat system with primer and wear coat
- 20-30 mils: a full broadcast system with flake or quartz loaded into the body
What Happens to Cracks and Control Joints?
A coating follows the slab it sits on, and Smithtown slabs move - the Islip station logs 101 days a year at or below freezing, and every one of them works on whatever cracks exist. Ask which cracks get filled and with what, and whether control joints get honored through the finish or filled flush. Neither answer is wrong by default: a joint carried through the coating shows as a clean line, while a joint filled rigid can telegraph a new crack beside it, and that trade-off belongs to the homeowner, decided before install day. Crack and joint repair walks through the options. A bid that never mentions joints has not looked closely at the floor.
Which Forecast Cancels Install Day?
This one is a trap question, in the best way. A real answer has numbers in it: substrate around 55F and rising for standard epoxies, and a slab surface at least 5F above the dew point so condensation never forms under a wet coat. September mornings here average 82 percent relative humidity, so dew point is not a theoretical concern - it is the difference between a floor that bonds and one that clouds and delaminates. An installer who says any day works, year-round, in an unheated bay, has answered a different question than the one asked. The right answer costs a reschedule now and then. The wrong one costs the floor.
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Quick Answers
How many garage floor coating quotes should you get?
Two or three, if they are comparable. Make each bid state the surface prep method, the moisture test and its number, and the system thickness in mils - otherwise a 3-5 mil film and a 20-30 mil broadcast system land on the same spreadsheet as if they were the same product.
What is the biggest red flag in a coating quote?
Silence on surface prep. A quote that never says how the slab gets ground - or that leans on acid etching alone - is describing a floor bonded to whatever the trowel left behind, and that is the failure mode behind most peeling garage floors.
Should coating thickness be written into the contract?
Yes, in mils per coat. Thickness is the spec that most separates one system from another, it is measurable on install day, and an installer confident in the build has no reason to keep it off the page.