PREP BEFORE GLOSS.

Why coatings peel

A floor coating holds on by bonding into the top of the concrete. Anything that gets between the two weakens that bond: oil, old sealers, paint, curing compounds, dust, or a dense, smooth surface layer. Moisture vapour pushing up from below can also build pressure under a coating and lift it.

None of that is visible once the floor is glossy, which is why preparation is the part of a quote worth asking the most questions about.

Surface profile: giving the coating something to grip

Coating manufacturers specify a surface profile, a measure of how rough the prepared concrete should be, in their installation instructions. The industry reference is the International Concrete Repair Institute's Concrete Surface Profile (CSP) scale, which runs from CSP 1 (nearly flat) to CSP 10 (very rough). Mechanical methods such as diamond grinding or shot blasting are the usual ways to reach the profile a product asks for.

Repairs come before coating

• Cracks are cleaned out and filled with a suitable repair material
• Spalled or pitted areas are patched and ground flush
• Joints are treated according to whether they move
• Oil-soaked areas are cleaned or removed so the coating can bond

Moisture testing: what the common tests measure

Two test methods appear in most coating manufacturers' instructions. ASTM F2170 measures relative humidity inside the concrete using probes placed in drilled holes. ASTM F1869 measures the moisture vapour emission rate at the surface using a sealed calcium chloride dish. Each product publishes its own limits for these results, and some primers are designed for slabs with higher moisture.

A simple plastic-sheet test (taping plastic to the slab and checking for condensation) can hint at a problem but is not a quantitative test.

Where moisture testing matters most in the GTA

• Basement slabs, which sit below grade and may have no vapour barrier underneath in older homes
• Slabs poured recently, which still release water as they dry
• Slabs with a history of damp patches, efflorescence or failed flooring
• Ground-floor commercial slabs where previous flooring trapped moisture

Questions to ask any contractor about prep

• How will you prepare the surface, and what profile does the product require?
• Will you test for moisture, and which method?
• What happens if the test result is outside the product's limits?
• How will cracks, joints and old coatings be handled?