Guide
Concrete floor preparation and moisture testing: where floors fail
Updated
Almost every resin floor failure is a bond failure or a moisture failure, and both are decided before the first bucket is opened.
Why preparation is the whole job
A resin floor is only as good as its grip on the concrete underneath. New slabs carry laitance, a weak surface layer that has to be removed. Old slabs carry oil, rubber, curing compounds, previous coatings and years of contamination. Preparation removes all of that and leaves a clean, open, mechanically keyed profile for the resin to bond into. It is the line on the quote most often trimmed and the one that most reliably destroys the floor when it is.
The three common methods
- Shot blasting
- Steel shot fired at the slab and recovered by vacuum. Fast over large areas, low dust when the equipment is working properly, and it leaves a consistent open profile. The default for warehouse-scale floors.
- Diamond grinding
- Grinds the surface flat and removes coatings and laitance. Better for edges, small areas, awkward shapes and where a flatter finish is needed. Slower per square metre than blasting on open floors.
- Scabbling or planing
- Aggressive mechanical removal for heavily contaminated or damaged slabs, or where levels have to come down. Noisy, dusty and slow, but sometimes the only route to a sound substrate.
Moisture: the failure nobody sees coming
Concrete releases moisture for a long time, and resin is largely impermeable. Trap moisture underneath and you get blistering, delamination and a floor that has to be taken up and done again. That is why moisture measurement before application is standard practice, and why the result can trigger a damp-suppressing primer or membrane, or simply a longer wait. A quote that does not mention moisture on a new or ground-bearing slab has left the risk with you.
Protecting yourself at quote stage
- Ask for the preparation method by name, not the word prepared.
- Ask whether moisture testing is included, when it happens, and what the price does if the reading is high.
- Ask what the contractor assumes about the substrate, and what the variation looks like if the slab is worse.
- Ask for a warranty, and read what it excludes. Most exclusions are about substrate and moisture, which tells you exactly where the risk sits.
- On a failing existing coating, ask whether it is coming off entirely or being overlaid, and why.
Blasting and grinding produce dust, noise and vibration, and on an occupied site they need containment and planning. That is a programme conversation as much as a cost one: see working around production.