When a resin floor fails, the conversation usually starts with the material. Wrong product, cheap system, poor quality supplier.
It's almost never that. Modern resin systems from reputable manufacturers are well-developed products with decades of refinement behind them. When a floor delaminates, blisters, or lifts in sheets eighteen months after installation, the cause is nearly always what happened before the resin was mixed.
That's an uncomfortable truth for the industry, because preparation is the invisible part — the part a client never sees, can't easily evaluate, and is most likely to view as a place to save money. It's also the part that determines whether the floor lasts fifteen years or two.
Resin Doesn't Stick to Concrete. It Sticks to What's On It.
This is the fundamental point, and it explains everything that follows.
A trowelled or power-floated concrete slab has a dense, closed surface. There's laitance on it — a weak layer of fine cement particles and water that rises during finishing. There may be curing compounds, which are specifically designed to prevent things bonding. There's likely oil, grease, tyre marks, old coatings, or whatever the building has been used for.
Apply resin directly to that and you've bonded an extremely strong material to a weak surface layer. The resin itself is fine. The laitance underneath it fails, and the floor comes away in sheets with a thin skim of concrete still attached to the back.
The purpose of Surface preparation is to remove that weak layer entirely and open up the concrete to create a mechanical key. Done properly, the resin bonds into the substrate rather than onto it, and the bond becomes stronger than the concrete itself.
The Preparation Methods, and When Each Applies
Three techniques dominate, and they're not interchangeable.
Diamond grinding uses rotating diamond-segment discs to abrade the surface. It removes laitance, flattens high spots, takes off thin coatings and produces a consistent, moderately open profile. It's the workhorse method for most commercial installations and the right choice where the slab is sound and the coating is relatively thin.
Effective Concrete grinding is more than running a machine over the floor once. It means progressive segment grades, multiple passes, and attention to edges and perimeters where machines don't reach — those unground margins are where failures frequently start.
Shot blasting propels steel shot at the surface at high velocity, removing the top layer and leaving a textured profile. It's faster over large open areas, produces a more aggressive key, and is generally the correct method for thicker systems that need deeper anchorage. It's less suited to confined spaces and leaves a coarser finish that isn't appropriate for thin coatings.
Scarifying or milling uses rotating cutters to remove material aggressively. This is for heavily contaminated slabs, thick failed coatings, or where significant levelling is required. It leaves a very rough surface that usually needs secondary preparation afterwards.
The profile produced is measurable — the industry uses the Concrete Surface Profile scale, running from CSP 1 for lightly acid-etched through to CSP 9 for heavily scarified. Each resin system specifies a required profile, and matching the preparation method to that specification is the contractor's job. A system requiring CSP 3 applied over a CSP 7 surface will consume far more material than quoted and may not achieve a proper finish.
Moisture: The Failure Nobody Sees Coming
If preparation is the most common cause of failure, moisture is the most expensive.
Concrete holds water. New slabs contain significant moisture from the mix and take a long time to dry — the rough guide is around a day per millimetre of thickness for the first 50mm under good conditions, which means a 150mm slab may need several months. Older slabs can take up moisture from the ground where there's no effective damp proof membrane, or where one has been compromised.
When resin is applied over a slab with excessive moisture, the water has nowhere to go. It accumulates at the interface, and osmotic pressure lifts the coating in blisters. These may appear within weeks or after a year, and once they start they spread.
The only way to know is to test. Hygrometer testing to BS 8203 measures relative humidity at the slab surface under a sealed hood, typically requiring readings below 75% RH for most resin systems, though specifications vary. This takes time — the hood needs to equilibrate, usually over 72 hours — which is precisely why it gets skipped when a programme is tight.
Where readings are too high, the answer is a moisture-tolerant primer or a surface damp proof membrane. These add cost, which is why a contractor who tests and reports a problem is sometimes perceived as creating one. The alternative is installing over a known risk and dealing with the consequences later.
Any contractor quoting a resin floor without testing moisture is guessing. It's a reasonable question to ask directly: will you test, to what standard, and what happens if the readings come back high?
Substrate Repair Comes Before Everything
Preparation also means fixing what's wrong with the slab.
Cracks need assessing for whether they're static or moving. Static cracks are routed out and filled with resin mortar. Moving cracks need a different approach entirely, because a rigid coating over an active crack will simply crack again — and here the correct answer is sometimes a movement joint rather than a repair.
Spalled areas, pitting and damaged sections need building back up with compatible repair mortar. Existing joints need to be carried through the new floor rather than coated over, because joints exist for a reason and burying them doesn't remove the movement.
Contamination deserves its own mention. Oil and grease that has penetrated into the slab will keep migrating upward and prevent bonding, and grinding alone won't fix it — the contaminated concrete needs removing entirely. Workshops, vehicle bays and food production areas are the common cases, and a contractor who tests a suspect area rather than assuming is doing you a favour.
Matching the System to the Use
With preparation handled, the system choice follows from what the floor actually has to withstand.
Thin film coatings at a few hundred microns suit light duty — storage, light assembly, areas where appearance and cleanability matter more than impact resistance.
Self-levelling screeds at 2–4mm give a smooth, seamless finish with better durability and good chemical resistance. The common choice for pharmaceutical, electronics, and clean manufacturing.
Heavy duty screeds at 4–9mm, including polyurethane systems, handle impact, thermal shock and aggressive chemicals. This is the correct specification for food and drink production, commercial kitchens, and anywhere steam cleaning or thermal cycling occurs — standard epoxy will fail under thermal shock where polyurethane won't.
Anti-slip systems incorporating aggregate are specified by the slip resistance required, measured by pendulum test value. Worth noting that anti-slip and easy-to-clean pull in opposite directions, so the specification should reflect the actual risk rather than defaulting to maximum texture.
Proper Industrial Resin flooring specification starts with the use case: what traffic, what loads, what chemicals, what temperatures, what cleaning regime, and what slip resistance is required. A contractor who asks these before quoting is specifying; one who doesn't is selling a system.
The Conditions on the Day
Even with good preparation, installation conditions matter.
Resin systems have temperature windows for both ambient and substrate. Too cold and cure times extend dramatically or the material doesn't cure properly. Too hot and pot life shortens, making application difficult. Substrate temperature needs to be above the dew point, or condensation forms on the surface during application and the bond is compromised.
Humidity affects some systems more than others, particularly moisture-sensitive products. And cure times between coats need respecting — rushing the overcoat window causes intercoat adhesion problems that show up later as delamination between layers rather than from the substrate.
What to Ask a Contractor
How will you prepare, and to what profile? The answer should reference the system specification.
Will you test for moisture, and to what standard? BS 8203 hygrometer testing, with a stated threshold.
What happens at edges, perimeters and around plant? This is where shortcuts hide.
How will you deal with existing joints and cracks? Carried through, not covered over.
What system, and why that one for this use? Specification should follow function.
What's the realistic programme, including cure times? A floor that needs seven days before heavy traffic needs seven days.
The Bottom Line
The resin is the visible part and the cheapest part of the decision. What determines whether a floor performs for fifteen years is whether the laitance came off, whether the moisture was tested, whether the cracks were dealt with properly, and whether the edges got the same attention as the middle.
A quote that's noticeably cheaper than the others is almost always cheaper on preparation, because that's where the hours are. It's also where the failures come from — so the saving is borrowed rather than real, and it gets repaid with the cost of taking the whole floor up and starting again.