A floor that fails usually fails at the concrete, not at the surface. What moisture, substrate strength and traffic class decide before any resin is chosen.
A production hall needs a new floor coating. Three quotes come in: one for a 400 micron epoxy, one for a 2 mm self-levelling system, one for a 4 mm mortar. They are not competing products. They are three different answers to different questions, and only one of them is matched to the traffic.
The concrete decides first
No resin will perform over a substrate it cannot bond to or that is releasing water vapour.
- Moisture content. A slab without a damp-proof membrane can transmit vapour indefinitely. Coating over it produces blisters and delamination, and the failure is often attributed to the coating.
- Surface strength. Weak, dusty or friable concrete fails cohesively before the coating fails adhesively. The test is simple and it is skipped more often than any other.
- Contamination. Oils, curing compounds and old adhesive residues block the bond. Mechanical preparation removes them; chemical etching does not.
- Preparation by mechanical means. Shot blasting or diamond grinding opens the surface and gives a profile. Acid etching is not an acceptable substitute for an industrial floor.
Then the traffic, then the chemistry
- Light duty, dry, pedestrian or occasional forklift. A high-build epoxy at 300 to 500 microns is adequate and economical.
- Medium duty, regular forklift traffic, some impact. Self-levelling epoxy at 2 to 3 mm, often with a quartz-filled body coat for impact resistance.
- Heavy duty, steel wheels, thermal shock, abrasive loads. Epoxy mortar at 4 to 6 mm, or a polyurethane screed where thermal shock and flexibility matter.
- Chemical exposure. Standard epoxy handles many dilute acids and alkalis. Vinyl ester is required for strong acids, oxidising agents and higher temperatures. Polyurethane is a poor choice for hot caustic.
- UV exposure or colour stability. Standard epoxy yellows and chalks under UV. Where appearance matters and daylight is present, a polyurethane or polyaspartic topcoat is the correct answer, over an epoxy body.
- Rapid return to service. Methyl methacrylate systems cure in one to two hours and allow traffic the same shift. They are the choice where the production line cannot stop for days.
The build-up, and why each layer exists
- Primer. Penetrates the concrete and seals it, and provides the bond for the body coat. On porous substrates a second primer pass is often needed.
- Body coat. Carries the thickness and the mechanical properties. This is where the impact and abrasion resistance lives.
- Topcoat. Provides the chemical resistance, the cleanability and the appearance. It is the thinnest layer and does the least structural work.
- Cove and detailing. Where hygiene or washdown matters, the floor-to-wall junction needs a coved detail, not a sealant bead.
The failure modes and what they indicate
- Blistering in patches. Vapour pressure from the slab. The moisture barrier or the moisture-tolerant primer was missing.
- Delamination at the edge or at cracks. Preparation or contamination, or movement in the slab that the coating could not accommodate.
- Cracking following the slab. The floor is moving and the coating is rigid. The answer is joint detailing and crack treatment, not a thicker coating.
- Wear through in wheel tracks. Under-specified for the traffic, or the wrong aggregate in the body coat.
- Loss of gloss and colour change. UV exposure on an epoxy topcoat.
Specification points that prevent most disputes
- State the traffic class and the chemical exposure, not just the product name.
- State the moisture limit and how it will be measured, and require the result before application.
- Require adhesion testing on the finished floor, with the test method and the acceptance value in the contract.
- Define the treatment of joints, cracks and drains, because these are where floors fail and where scope is most often ambiguous.
- Define the return-to-service time, so that the programme and the chemistry are compatible.
A floor is the one coating that is judged by everyone who walks on it, and it is installed over the substrate that is least controlled. Getting it right is mostly a matter of measuring the concrete and matching the system to the load, which happens before anyone opens a tin.