Concrete Epoxy: Coating & Painting Concrete Floors
Updated 14 October 2026
Concrete epoxy can make a dull, dusty slab look and perform like a finished floor, but concrete is not a blank canvas. It is porous, it holds moisture, it can be contaminated with oil or old sealers, and new and old slabs behave very differently. Most failed concrete epoxy coatings fail because of the concrete, not the epoxy.
This guide is all about the substrate: how to test concrete before coating it, how new and old slabs differ, what moisture vapour does to epoxy, what surface profile you need, and where epoxy for concrete works indoors and out. For an overview of systems, finishes and room-by-room advice, start with our epoxy floor guide.
Why concrete needs special treatment
Epoxy bonds to concrete in two ways: chemically, and mechanically by locking into the tiny pores and texture of the surface. Anything that blocks those pores (dust, laitance, oil, curing compounds, old sealer) or pushes the coating away from beneath (moisture vapour, efflorescence salts) weakens the bond. A concrete epoxy floor is only ever as strong as the top few millimetres of the slab it sits on.
Testing your concrete before applying epoxy
Moisture test
Moisture rising through concrete is the leading cause of blistering and delamination. A simple DIY check is the plastic sheet test: tape a 45 × 45 cm square of clear polythene to the slab on all four edges and leave it for 24–48 hours. If droplets form under the plastic or the concrete darkens, moisture is coming through. Professionals use calcium chloride or in-slab relative humidity probes for a measured reading; many epoxy systems specify a maximum, so check the product data sheet.
Water drop test for sealers and contamination
Sprinkle water across the floor. If it soaks in and darkens the concrete within a minute or two, the surface is porous enough to accept epoxy. If it beads, there is a sealer, curing compound, wax or oil present that must be removed by grinding.
Strength and soundness
Scratch the surface with a screwdriver or key. If it powders easily, there is weak laitance on top that must be ground off. Tap the slab with a hammer; hollow sounds can indicate delamination or voids that need repair first.
Old coatings
Test any existing paint by scoring a crosshatch with a knife and pressing tape firmly over it. If the coating lifts, it must come off. Coating over unknown paint is a gamble even when it seems firmly stuck.
New concrete vs old concrete
| New slab | Old slab | |
|---|---|---|
| Wait time | Typically at least 28 days of curing before epoxy | Ready once clean, dry and sound |
| Main risk | Residual moisture, laitance, curing compounds | Oil, old sealers, cracks, rising damp |
| Preparation | Grind to remove laitance and curing membranes | Degrease, repair, grind away coatings |
| Moisture | Often high – test before coating | Depends on damp-proof membrane |
Fresh concrete releases a lot of water as it cures. Even when it looks dry on top, a new slab can carry enough moisture to lift a coating. Some systems offer moisture-tolerant primers designed for green or damp concrete; follow their stated limits exactly.
Moisture vapour and epoxy concrete floors
Most UK homes built in recent decades have a damp-proof membrane under ground-floor slabs, but older properties, garages, outbuildings and basements often don’t. Without one, water vapour passes up through the slab continuously. Epoxy is an effective vapour barrier, so the vapour gets trapped beneath it, builds pressure and causes blisters and peeling.
Options if your slab is damp:
- Fix the source first – blocked drainage, poor ground levels or failed gutters.
- Use a moisture-mitigating epoxy primer rated for the readings you have.
- Choose a breathable concrete floor paint or sealer instead of a full epoxy system.
- Ask a professional to assess basements and below-ground slabs.
Surface profile: what CSP means
The industry describes concrete texture using Concrete Surface Profile (CSP) levels, from CSP 1 (almost flat, like an acid-etched finish) to CSP 10 (very rough, heavily scarified). Thin epoxy coatings typically need around CSP 2–3, roughly the feel of medium sandpaper. Thicker self-levelling systems often call for CSP 3–5.
| Preparation method | Typical profile | Suits |
|---|---|---|
| Acid etching | CSP 1–2 | Thin water-based coatings on porous concrete |
| Diamond grinding | CSP 1–3 | Most DIY and pro epoxy for concrete |
| Shot blasting | CSP 2–5 | Thicker systems, larger areas (usually pro) |
| Scarifying | CSP 4–9 | Removing thick coatings, heavy-duty overlays |
Diamond grinding with dust extraction is the most reliable DIY option. Wear an FFP3/P3 respirator, goggles and ear defenders, and keep others out of the area – concrete dust contains crystalline silica.
How to apply epoxy paint for concrete
- Clean and degrease the slab, then rinse and let it dry fully.
- Repair cracks, joints and spalls with epoxy mortar or crack filler.
- Profile by grinding to the CSP your system requires and vacuum thoroughly.
- Prime with a penetrating epoxy primer on porous or dusty concrete.
- Apply the body coat, mixing only what you can use within the pot life. Our guide on how to use epoxy resin covers ratios and timing.
- Add decoration such as flakes, quartz or metallic epoxy pigments if desired.
- Topcoat, adding anti-slip grit for wet areas.
- Cure in the product’s temperature range, typically 15–25°C, with the slab at least 3°C above dew point.
Ventilate well and wear nitrile gloves, eye protection and a respirator with organic vapour cartridges in enclosed spaces. For quantities, our how much epoxy do I need guide explains the coverage maths; porous concrete typically drinks more on the first coat.
Indoor and outdoor concrete epoxy uses
Indoors
- Garages and workshops – the most common use; see our epoxy garage floor guide for coatings, flakes and hot-tyre advice.
- Basements and cellars – seals dust, but moisture testing is essential.
- Utility rooms and kitchens – seamless and easy to clean.
- Polished-look living spaces – clear or metallic epoxy cement floors over a sound screed.
Outdoors
Standard epoxy is a poor choice for patios, paths and driveways. Ultraviolet light makes it yellow and chalk, and outdoor slabs move with temperature and moisture. If you want a coating outside, look for UV-stable polyurethane, polyaspartic or purpose-made exterior concrete coatings, and read our guide to UV-resistant epoxy resin to understand the limits. Covered areas like carports and porches can work with an epoxy base and UV-stable topcoat.
Concrete epoxy coating cost
Typical ranges for coating concrete floors:
- DIY epoxy paint for concrete: typically £5–£15 per m² ($0.50–$2 per sq ft).
- DIY 100% solids or flake systems: typically £12–£30 per m² ($1.50–$4 per sq ft).
- Professionally installed systems: typically £40–£100+ per m² ($4–$12+ per sq ft), depending on prep and finish.
Budget separately for grinder hire, repairs and primers; on poor slabs, preparation can cost as much as the coating.
Common mistakes
- Coating new concrete before it has cured.
- Skipping the moisture test.
- Relying on acid etching over dense or sealed concrete.
- Leaving grinding dust on the surface.
- Using interior epoxy outdoors in full sun.
Moisture is the most common reason coatings fail on a slab. The US National Institutes of Health facilities team explains vapour pressure in concrete and how to test for it, comparing the calcium chloride test with in-slab relative humidity probes.
Watch it being made
See one of our tables come together in the workshop: a nebula resin top with fibre optic stars, from the first pour to the lights going on.
Resin art nebula resin table with fibre optic art. More builds on the Go Bespoke YouTube channel.
Frequently asked questions
Can you put epoxy on concrete?
Yes – concrete is the most common base for epoxy flooring. It must be clean, dry, sound and profiled so the epoxy can bond.
How long should concrete cure before epoxy?
Typically at least 28 days, and longer in cold or damp conditions. Test moisture before coating regardless of age.
What is the difference between epoxy paint and epoxy coating for concrete?
Epoxy paint usually refers to thinner, often water-based, one- or two-part products. A true epoxy coating is a two-part system that builds a thicker, harder film with better durability.
Can epoxy be used on outdoor concrete?
Not in direct sun without a UV-stable topcoat; standard epoxy yellows and degrades outdoors. Exterior coatings designed for UV are a better choice.
Do I need to grind concrete before epoxy?
In most cases yes. Grinding removes laitance, sealers and contamination and gives the surface profile epoxy needs. Acid etching is a lesser alternative only on porous, uncontaminated slabs.
Learn more
Concrete prep is hard, dusty work, but it is the part that decides whether your floor lasts. For more practical resin know-how, follow our workshop builds on the Go Bespoke YouTube channel.
