Epoxy Floor Coating Over a Damp Concrete Slab
You are applying a two-pack epoxy floor coating to a 120 square metre concrete garage slab in a new commercial building. The slab is 28 days old but has no damp-proof membrane beneath it. A moisture test shows readings above the coating manufacturer's maximum. The surface has a power-trowelled, glossy finish, and there are two shallow cracks. The client wants the floor in service within 48 hours because equipment arrives then. The data sheet specifies a 7-day full cure before heavy traffic, and requires the substrate to be within a stated moisture range. Ambient temperature is 22 degrees Celsius.
1. Assess whether the slab is suitable for the specified epoxy and explain what you would do about the moisture and surface condition.
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The slab is not suitable as it stands. The moisture readings exceed the manufacturer's maximum, and with no damp-proof membrane the moisture will continue to rise through the slab. Coating over it risks blistering, loss of adhesion, and delamination. I would not apply the epoxy until the moisture issue is resolved.
Options include allowing further drying time with the slab protected from rain, or using a moisture-tolerant primer or coating system rated for the measured conditions, if the manufacturer confirms it. The glossy, power-trowelled surface also needs mechanical preparation such as grinding or shot blasting to provide a profile for adhesion, and the two cracks need routing and filling with a compatible repair before coating.
I would document the moisture readings and get written confirmation from the manufacturer that the chosen system suits the substrate.
2. The client insists on 48-hour service. How do you respond, and what would you propose?
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I would refuse to put the floor into service in 48 hours. The data sheet requires 7 days for full cure before heavy traffic, and the moisture problem is unresolved. Overriding either control risks a failed floor that would cost far more to fix than a delay.
I would explain the risks to the client in writing and propose alternatives: extend the program to allow drying, preparation, coating, and full cure; stage the work so equipment is installed on a protected temporary surface in part of the area while the coating cures; or, if the manufacturer approves a system suited to the moisture level, use that and still observe its cure time. Any change must be confirmed against the data sheet, and the client's instruction recorded.
3. Describe the preparation and inspection steps you would use to give the coating the best chance of success.
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Preparation would include mechanical grinding or blasting to remove the glossy surface and open the profile, crack routing and filling, and thorough cleaning and dust removal. I would re-test moisture after preparation and confirm it is within the approved range before priming.
Inspection would cover surface profile, crack repairs, and cleanliness before coating. During application I would check coverage and film thickness, and after cure I would inspect for blistering, pinholing, and adhesion. I would record moisture readings, preparation method, product batches, and cure times, and hold the floor out of service for the full cure period before sign-off.