Epoxy Resin Floor Preparation: Getting the Base Right

Master the critical preparation stage of epoxy flooring. Proper prep prevents 90% of failures – learn the professional techniques that ensure lasting results.

Why Preparation Matters More Than Application

The old saying 'proper preparation prevents poor performance' has never been more true than with epoxy flooring. You can use the best materials and most experienced applicators, but if the substrate isn't properly prepared, the floor will fail. Bubbling, peeling, and delamination almost always trace back to inadequate preparation.

In our 20+ years installing epoxy floors across the UK, we've seen countless failures from other contractors who rushed the prep stage. We've also rescued these floors, and the repairs always cost more than doing it right the first time.

Step 1: Assessing the Substrate

Start with a thorough visual inspection. Look for cracks, oil stains, existing coatings, and areas of weak or friable concrete. Use a coin or screwdriver to scratch the surface – if it crumbles easily, you'll need to grind back to sound concrete.

Check for flatness using a 2-metre straight edge. High spots and dips greater than 3mm should be ground or filled. commercial kitchens and food production areas require particularly flat surfaces for hygiene and drainage.

Step 2: Moisture Testing (The Critical Step)

Moisture is the number one enemy of epoxy flooring. Even concrete that looks and feels dry can contain enough moisture to cause total failure. You must test before coating.

The plastic sheet test is simple but effective: tape down 1m² of heavy plastic sheeting, seal all edges, and leave for 24 hours. If you see condensation or darkening of the concrete underneath, the slab is too wet for epoxy.

For accurate readings, use a concrete moisture meter. Levels above 75% relative humidity require moisture remediation – either extended drying time, dehumidification, or a moisture-blocking primer system.

Step 3: Mechanical Surface Preparation

Diamond grinding is the gold standard for epoxy floor prep. It removes surface laitance (the weak cement layer), opens the concrete pores, and creates an ideal profile for mechanical bonding. Aim for a CSP 2-3 profile (Concrete Surface Profile).

Shot blasting is faster for large areas but creates a rougher profile. It's excellent for industrial settings where texture isn't a concern. For hospitals where a smooth, hygienic finish is essential, grinding is preferred.

Always start with coarser grits (30-40) for heavy contamination or existing coatings, then progress to finer grits (80-120) for the final profile. Work systematically in overlapping passes to ensure even coverage.

Surface Preparation Methods Compared

Step 4: Crack and Joint Repair

Clean out all cracks and control joints with a grinder or router to create a clean V-shape. Blow out dust with compressed air, then fill with flexible epoxy crack filler. For cracks wider than 3mm, use a quartz-filled epoxy compound for added strength.

Expansion joints require special treatment – they must remain flexible. Use a polyurethane sealant rather than rigid epoxy, and ensure the joint is clean and dry before application.

Step 5: Thorough Cleaning

After mechanical prep, the floor must be spotless. Use an industrial vacuum with HEPA filtration to remove all dust. Then clean with a degreaser or TSP solution to remove any oils or contaminants.

Rinse thoroughly with clean water and allow to dry completely. We usually leave floors to dry for 24 hours minimum, longer in humid conditions. Use industrial fans and dehumidifiers to speed the process if needed.

Step 6: Priming

The primer seals the concrete, improves adhesion, and helps you identify any remaining contamination. A good primer will soak into clean concrete; if it pools or stays on the surface, there's still contamination that needs addressing.

For standard concrete in good condition, use a penetrating epoxy primer. For porous or damaged substrates, use a moisture-tolerant primer. The primer should be applied at the specified coverage rate – too thin and it won't seal properly, too thick and you're wasting material.

Primer Selection Guide

Common Preparation Mistakes

• Skipping moisture testing – the fastest way to total failure
• Inadequate grinding – if you can still see a shiny surface, you haven't ground enough
• Not removing all dust – even a thin layer prevents proper adhesion
• Working in cold or humid conditions – both extend cure times and risk condensation
• Applying primer too thickly – it needs to penetrate, not sit on top
• Rushing between stages – each step needs proper cure time

When to Call Professionals

Large commercial areas require industrial grinding equipment and experienced operators. The wrong technique can damage the substrate or create an uneven profile that shows through the final coating.

If you're weighing up the DIY approach, our comprehensive guide to DIY vs professional installation covers the equipment costs, skill requirements, and realistic timeframes.

Once your floor is properly installed, knowing how to maintain it ensures it lasts for decades. Our maintenance guide covers daily cleaning, periodic deep cleaning, and when to recoat.