A high build epoxy resin floor is only as good as the concrete beneath it. Get the preparation right and the floor will resist heavy traffic, chemicals and impact for many years. Get it wrong and even the best resin can bubble, peel or delaminate within months.
At SP Bespoke Resin Flooring, we specialise in epoxy resin flooring for residential and commercial clients, including high build and decorative epoxy systems. In this guide, we explain the steps we follow to prepare concrete correctly before a single drop of resin is mixed. You can see examples of our finished floors at www.spbespokeresinflooring.co.uk and on our social media channels.
Why concrete preparation matters
Epoxy resin bonds to concrete in two ways: it soaks into the pores of the surface and it grips the texture left by preparation. High build systems, which are applied thicker than standard coatings, put more stress on that bond. They carry heavier loads and cure with more internal shrinkage, so the substrate has to be sound, clean, dry and properly profiled.
Most resin floor failures trace back to the concrete, not the resin. The usual causes are:
- Laitance (a weak, powdery surface layer) left on the slab
- Moisture rising through the concrete
- Oil, grease or old sealers contaminating the surface
- Cracks, holes and uneven areas that were never repaired
- Too little surface texture for the resin to grip
Step 1: Assess the slab
Every job starts with a proper survey of the existing concrete. We look at:
- Age and cure: New concrete should normally be left to cure for at least 28 days before coating, and often longer if it is thick or the weather has been damp.
- Strength and soundness: The concrete needs to be strong enough to hold a thick resin system. Soft, crumbling or flaking areas have to be removed or repaired.
- Contamination: Oil stains, grease, paint, old sealers, adhesive residues and curing compounds all stop resin from bonding.
- Existing damage: Cracks, spalling, holes, uneven joints and previous patch repairs all need to be identified and planned for.
- Damp-proof membrane: We check whether a damp-proof membrane (DPM) is present beneath the slab, as this strongly affects moisture risk.
This assessment lets us specify the right preparation method and resin system for your floor, rather than guessing once work has started.
Step 2: Test for moisture
Moisture is the most common hidden cause of epoxy floor failure. Water vapour moving up through a slab can push a resin coating away from the concrete, causing blisters, bubbles and loss of adhesion.
Before coating, we test the slab using recognised methods such as a relative humidity test or a moisture meter reading. As a general guide, concrete should be dry enough to meet the resin manufacturer's limits, commonly around 75% relative humidity or below for standard epoxy systems.
If readings are too high, or the slab has no effective DPM, we do not simply coat over the problem. Instead we can apply a specialist moisture-tolerant primer or a damp-proof epoxy membrane, designed to block rising moisture and protect the finished floor.
Step 3: Mechanical preparation
Resin will not bond reliably to a smooth, glazed or laitance-covered surface. Mechanical preparation removes the weak top layer and opens the pores of the concrete, leaving a clean, textured profile for the resin to grip. Acid etching and light sanding are not enough for a high build floor.
Method
Diamond grinding Most residential and commercial floors Removes laitance, levels minor high spots and leaves a fine, even profile
Shot blasting Large areas and heavy-duty floors Fast, dust-controlled and creates a consistent profile for thick systems
Scarifying Thick coatings, heavy contamination, badly uneven slabs Aggressive removal, usually followed by grinding or repair work
We choose the method according to the condition of the slab and the thickness of the system being installed. All of our preparation is carried out with dust extraction, which keeps your property or site cleaner and gives a better result.
Step 4: Clean, degrease and remove dust
Once the surface has been ground or blasted, it must be completely clean. Fine concrete dust left on the slab acts like a layer of talc between the concrete and the resin, and will weaken the bond.
Our team will:
- Vacuum the whole floor with an industrial dust extractor
- Treat any oil or grease contamination with a suitable degreaser, then re-grind or remove deeper staining where needed
- Sweep and vacuum again, including edges, corners and around fixed obstacles
- Inspect the floor to confirm it is dry, dust-free and ready for repairs and priming
Step 5: Repair cracks, joints and damage
A high build resin floor will show every flaw underneath it, so repairs are made before any coating goes down.
- Cracks: Active cracks are assessed first. Stable cracks are chased out and filled with a rigid epoxy repair mortar or resin, often with stitching bars across larger cracks.
- Holes and spalled areas: Damaged concrete is cut back to a sound edge and filled with a fast-curing repair mortar.
- Expansion and construction joints: Movement joints are kept and treated with a flexible sealant, rather than being filled with rigid resin that would crack.
- Uneven or low areas: Dips and rough patches are levelled with a resin-based screed or smoothing compound so the finished floor lies flat.
Taking time over this stage is what gives a seamless, professional finish, particularly with decorative epoxy flooring where the surface is on show.
Step 6: Prime the concrete
The final step before the main resin layer is a suitable epoxy primer. The primer soaks into the prepared concrete, seals the pores and creates the strong bond that the high build coat depends on. It also helps prevent pinholes and bubbles caused by air escaping from the slab as the resin cures.
We select the primer to suit the slab, with moisture-tolerant primers where needed, and in some cases we add a light sand broadcast into the wet primer to give the next layer extra grip. The primer is applied within the manufacturer's recommended time window, and we follow the correct overcoating times so the layers bond chemically rather than sitting as separate skins.
Common preparation mistakes to avoid
If you are comparing quotes or considering a DIY job, watch out for these shortcuts:
- Coating new concrete before it has fully cured
- Skipping moisture testing, or ignoring a high reading
- Using acid etching or a quick sand instead of diamond grinding or shot blasting
- Painting over oil-stained or contaminated concrete
- Leaving dust behind, or not repairing cracks and holes
- Applying resin outside the recommended temperature range, which affects curing and bonding
Any one of these can lead to peeling, bubbling or cracking, and the cost of stripping and redoing a failed floor is far higher than doing the preparation properly the first time.
Get your concrete floor prepared properly
At SP Bespoke Resin Flooring, we treat preparation as the foundation of every high build and decorative epoxy resin floor we install, for homes and commercial spaces alike. Our specialists assess your slab, test for moisture, prepare the surface and repair any defects so your new floor looks excellent and lasts.
Ready to talk about your project? Visit www.spbespokeresinflooring.co.uk to request a quote, and follow our social media channels to see recent projects, before-and-after transformations and floor care tips.