He had done the square footage. He had priced the epoxy system — two-part epoxy base coat, broadcast chip, polyaspartic topcoat. Material cost was tight, labor was tight, margin was where it needed to be. He sent the proposal at $14,800 for a 2,500-square-foot commercial garage floor.
The client signed the same afternoon.
He showed up Monday morning with his crew, his grinder, and his materials.
By 10 AM he knew the floor was wrong.
The concrete had been coated before — a penetrating sealer, probably applied three or four years ago. The surface would not accept the epoxy without full diamond grinding down to bare concrete. Not the light prep he had priced. Full removal.
By Tuesday afternoon he knew the floor was worse than wrong.
The moisture vapor emission test he ran — the calcium chloride test required before any epoxy system on a slab-on-grade — came back at 11 pounds per 1,000 square feet per 24 hours. The epoxy manufacturer's maximum was 5. He needed a moisture mitigation system before the epoxy could go down.
Grinding: $2,200 he had not priced.
Moisture mitigation: $1,875 he had not priced.
Total unpriced work: $4,075.
Total margin on the job: $3,950.
The floor finished on schedule. The client was satisfied. The job lost money.
Why Epoxy Prep Gets Underpriced
Epoxy flooring estimates have a structure problem that is almost universal in the industry.
The epoxy system itself — base coat, broadcast, topcoat, primer if needed — is priced by the square foot from known material costs and familiar labor rates. A contractor who has installed a hundred floors knows what a polyaspartic topcoat costs per square foot within a few cents, and what his crew will produce in a day. The epoxy system gets priced correctly.
The prep work does not.
Prep is priced as a flat percentage of the total job — "I always allow 15 percent for prep" — or as a fixed line item that reflects what prep looked like on the last job, regardless of what this job's concrete will require. Both approaches produce the same result: a prep allowance that is accurate when the concrete is clean and simple, and catastrophically inaccurate when it is not.
The problem is that the contractor does not know what the concrete will require until he shows up. The site visit before the bid shows him the floor dimensions and the general condition. It does not show him what is under the surface — the old sealer, the moisture load, the contamination, the history of the slab.
Add-On 1: Grinding
Surface preparation for epoxy is not uniform. It ranges from a light diamond grind to open the concrete pores, to full shot blasting or heavy grinding to remove previous coatings, contamination, or damaged surface layers.
The range in labor and equipment cost across that spectrum is significant.
Light prep — a single-pass grind on clean, uncoated concrete — runs $0.40 to $0.75 per square foot in equipment time and labor. On a 2,500-square-foot floor, that is $1,000 to $1,875. Reasonable to carry in the estimate.
Medium prep — removal of a failed or incompatible previous coating, surface contamination cleanup, or two-pass grinding on harder concrete — runs $0.80 to $1.25 per square foot. On the same floor: $2,000 to $3,125. Already above a standard prep allowance on a $14,800 job.
Heavy prep — removal of a penetrating sealer or deeply contaminated surface requiring full diamond grinding to bare concrete, multiple passes, edge grinding, and contamination disposal — runs $1.50 to $2.00 per square foot or more. On a 2,500-square-foot floor: $3,750 to $5,000. This is what the Monday morning floor required.
The contractor priced light prep. The floor needed heavy prep. The gap was $2,200.
The information that would have caught this — the existence of the prior sealer — was visible on the floor. It read as a slight sheen on the surface, a uniformity of texture that bare concrete does not have. A site visit with prep assessment in mind, rather than just dimension verification, would have flagged it.
Add-On 2: Moisture Mitigation
Every concrete slab-on-grade transmits moisture vapor from the ground through the slab to the surface. Epoxy and polyaspartic coatings are vapor barriers — they stop that transmission. If the vapor emission rate is above the coating manufacturer's threshold, the trapped moisture builds pressure between the coating and the concrete and causes delamination, bubbling, or failure within months.
The industry standard test is ASTM F1869 (calcium chloride) or ASTM F2170 (relative humidity probe). Most coating manufacturers require testing before application on any slab-on-grade and will void their warranty if the test is skipped.
The acceptable emission rate for most epoxy systems is 3 to 5 pounds per 1,000 square feet per 24 hours. When a slab tests above that threshold, a moisture mitigation system is required before the coating goes down.
A moisture mitigation system — typically a two-component epoxy vapor barrier applied to the prepared concrete before the decorative system — costs $0.65 to $1.25 per square foot in materials and labor, plus the cost of the test itself ($75 to $150 per test, with three to four tests needed on a 2,500-square-foot floor).
On the commercial garage floor: $1,625 to $3,125 for the mitigation system, plus $300 in testing. The job required $1,875 in mitigation work that was not in the estimate because no one ran the test before the proposal went out.
The calcium chloride test costs $300 and takes 72 hours. The moisture mitigation system it triggers costs $1,875. The delamination warranty claim it prevents costs $14,800 in rework and a destroyed client relationship.
The test should be in every epoxy estimate on every slab-on-grade. Not as an option — as a line item.
The Two Numbers Every Epoxy Estimate Needs Before It Goes Out
These are not unknowable add-ons. They are calculable from the floor — if the floor is assessed for them specifically before the proposal is submitted.
Grinding level: Walk the floor before the bid with prep assessment as the explicit purpose. Look for prior coatings — the sheen, the color uniformity, the way the surface responds to a scratch test. Ask the client what has been applied to the floor in the past five years. If there is any indication of a prior coating or penetrating sealer, price medium to heavy prep. Do not assume clean concrete.
On a 2,500-square-foot floor, the difference between light prep and heavy prep is $2,500 to $3,000. That difference should be in the estimate, not discovered on Monday morning.
Moisture level: Run the test, or require the client to provide recent results, before the proposal is finalized. A calcium chloride test placed Friday is readable Monday. The result either confirms that a standard prep budget is sufficient, or it triggers a moisture mitigation line item that is priced accurately and included in the contract before anyone commits to a margin.
On a 2,500-square-foot floor, moisture mitigation ranges from $1,600 to $3,000 depending on the emission rate and the mitigation system required. An estimate that carries a $0 moisture line item is either lucky or wrong.
What the Job Looked Like If the Prep Was Priced
The floor had a prior penetrating sealer. That was visible. The slab was on-grade in a commercial building with no vapor barrier. Moisture testing was not optional.
An estimate built from those two assessments — not from a flat prep percentage — would have included:
Heavy grinding at $0.88 per square foot: $2,200.
Moisture testing (4 tests): $300.
Moisture mitigation system at $0.75 per square foot: $1,875.
Total prep line items: $4,375.
Total proposal with accurate prep: $19,175.
Whether the client signs at $19,175 is a different question. He might. The floor needed what it needed — that number reflects real scope, and a client who understands that a prior sealer and high moisture require additional prep may accept it. Or he shops it and finds someone who prices it wrong and then either eats the add-ons or walks off the job.
Either outcome is better than what happened: $14,800 to do a $18,725 job, with a margin that disappeared before the first bucket of epoxy was opened.
The prep cost is not a surprise. It is a site condition that was there to be assessed before the bid. Pricing it requires looking for it — not hoping it matches the last job.
For how TIM handles flooring takeoffs and flags prep requirements from scope documents: Drop the File. TIM Builds the Takeoff.
For the full cost of estimating overhead when most bids are built from assumptions: You Wrote Four Estimates This Week. You'll Get Paid for One.