When Should You Use Epoxy Grout and How Is It Applied?

Quick Answer: Epoxy grout (two- or three-part resin and hardener system) is used where chemical resistance, total waterproofing or zero porosity is required — wet rooms, commercial kitchens, swimming pools, and joints subject to staining. It is installed to BS 5385-3:2014 and BS EN 13888:2009 (Reaction Resin grout, classification RG). It has roughly 45–90 minutes pot life, costs 4–6× cementitious grout, and demands disciplined cleaning during the haze stage to avoid permanent residue.

Summary

Epoxy grout is a thermosetting resin system mixed on site from two components (resin and hardener) — or three, where coloured filler is supplied separately. Unlike cementitious grout (which is hydraulic and stays slightly porous), epoxy grout cures into a dense, non-absorbent, chemically inert joint. That makes it the default specification for environments where ordinary grout would stain, soften or harbour bacteria.

The most common UK applications are commercial kitchens (where animal fats and cleaning chemicals would destroy cement grout), wet rooms and shower areas (where waterproofing of the joint matters as much as the surface), and breweries, dairies, laboratories and food-processing floors. Domestic uses are growing: kitchen splashbacks, shower trays and pool surrounds.

The trade-off is application difficulty. Epoxy is sticky, sets fast and is unforgiving — leftover residue cures rock-hard within 24 hours and is then almost impossible to remove without damaging the tile. Many tilers add 25–40% to their day rate when quoting epoxy, both because of slower coverage and because the cleaning window is tight.

Key Facts

• Classification — Reaction Resin (RG) grout per BS EN 13888:2009; cementitious grouts are CG1 (normal) or CG2 (improved performance)
• Pot life — typically 45–90 minutes at 20°C; reduces sharply above 25°C
• Full cure — 7 days before exposure to chemicals or heavy washdown; 24h foot traffic
• Shrinkage — effectively zero (cementitious grout shrinks 2–4% on cure)
• Water absorption — <0.1% (BS EN 12808-5); cementitious CG2 grout is ~3%
• Compressive strength — 45–60 N/mm² (cementitious CG2 ~15–25 N/mm²)
• Joint width range — most epoxies suit 2–15mm; check manufacturer (some are formulated for 1–3mm only)
• Working temperature — 10–30°C for application; below 10°C cure slows dramatically
• Pack size — typically 2.5kg, 5kg or 10kg pre-weighed kits (do not split a kit)
• Coverage — varies by tile size; e.g. 600×600×10mm joints at 3mm use ~0.4kg/m²
• Standards — BS 5385-1, BS 5385-3, BS 5385-4 (covers wall, floor and external tiling installation)
• HSE classification — uncured epoxy resin and amine hardener are sensitisers — RPE not always needed but skin contact must be avoided
• Cost — £35–£70 per 5kg kit retail (cementitious is £6–£12 per 5kg)
• Cleaning agent — manufacturer-specific epoxy residue remover; never solvent or vinegar on cured residue
• Compatibility — bonds to ceramic, porcelain, natural stone, glass mosaic; check natural stone (some absorb pigment — seal first)

Quick Reference Table

Detailed Guidance

Choosing between epoxy and cementitious

The rule of thumb: if the joint will see chemicals, heavy water exposure or stain risk that ordinary grout can't handle, specify epoxy. Otherwise an improved cementitious grout (CG2 to BS EN 13888) with a quality sealer will usually do the job for half the cost and twice the application speed.

Specific drivers for epoxy:

• Continuous water immersion (pools, fountains)
• Chemical exposure (acids, alkalis, oils, solvents)
• High hygiene requirement (food prep, medical, laboratory)
• Joints visible on a high-end install where staining would be obvious
• External joints subject to freeze–thaw and chloride attack
• Coloured glass or translucent mosaics where cement haze would dull the tile

Cementitious CG2 is fine for:

• Normal domestic bathrooms (with adequate ventilation)
• Kitchen floors away from heavy oil exposure
• Hallways, lounges, dry living areas
• Most external patio installs where a sealer is applied

Mixing the grout

Epoxy grout is supplied as a pre-weighed system — typically a 2.5kg or 5kg bucket of resin/filler and a smaller part-A or part-B hardener. The ratios are fixed and non-negotiable. Never split a kit (proportions go wrong and the grout will be soft or won't cure).

Mix Sequence (typical 2-component product)
1. Empty hardener into resin bucket completely
2. Mix with paddle on slow drill (300-400 rpm) for 2-3 minutes
3. Scrape sides and bottom — unmixed pockets = soft grout
4. Continue mixing 1 minute more
5. Decant a working portion to a board (don't leave full bucket in sun)
6. Apply only what you can clean off in 20-30 minutes

Pot life starts the moment hardener touches resin. On a 25°C summer day a 5kg kit may be unworkable in 30–40 minutes; in a cool winter site it might give a comfortable 90 minutes. Plan small bays and clean as you go — never grout a whole bathroom floor in one mix.

Application

Apply with a hard rubber float held at 60° to the surface, pressing the grout firmly into every joint. Pull diagonally across the tile face to avoid dragging grout back out of the joint. Coverage rate is slower than cementitious — expect 4–6m² per hour of joint cleaning compared to 8–10m² for ordinary grout.

The critical phase is haze removal. As soon as the surface dulls but the joint is still tacky (typically 15–30 minutes after spreading), begin cleaning with:

1. A clean sponge dipped in warm water with the manufacturer's emulsifier additive
2. Wipe in a tight circular motion to break the epoxy film
3. Rinse the sponge constantly — every wipe with a dirty sponge re-deposits epoxy
4. Follow up with a clean, almost-dry microfibre to dry the tile

If a second-stage haze appears overnight, use the manufacturer's residue remover — never use solvent, vinegar or abrasive pads on porcelain or polished stone without testing first.

Common faults

Movement joints

BS 5385-3 requires movement joints in tiled floors at room perimeters, at internal corners, around fixed objects, and at intervals not exceeding 8–10m in internal floors. Epoxy grout is not a movement joint — it is rigid. Always use silicone or polysulphide sealant in movement joint locations, with backing rod where required.

Cost build-up for a typical quote

For a 10m² wet room shower floor with 600×600mm porcelain:

• Tile area ~ 27 joints across, similar count down → ~22m of joint at 3mm width
• 5kg epoxy kit at ~£55 → covers approximately this area with some waste
• Labour: 4–5 hours grouting and cleaning vs 2 hours for cementitious
• Add 30–40% to grout-stage day rate compared to standard CG2

Tradespeople often quote epoxy as a line item separately rather than absorbing the cost into the tiling day rate.

Frequently Asked Questions

Can I mix part of a kit?

No. Pre-weighed kits are formulated for the exact ratio printed on the pack. Splitting the kit by eye almost always produces a grout that is either too soft (excess resin / not enough hardener) or too brittle. If you need less than a full kit, mix the whole thing and decant only what you can use, then discard the rest before pot life expires.

Can epoxy grout be used over old cementitious grout?

Not directly. Old grout must be raked out to at least the depth of the new joint (typically 4–5mm minimum) and the joint thoroughly vacuumed and dried. Epoxy needs to bond to the tile edge, not to old, contaminated cement. Use a multi-tool with a grout-rake blade.

Is epoxy grout safe to use on natural stone?

It can be, but stone must first be sealed with a stone impregnator. Unsealed marble, travertine, limestone and slate will absorb pigment from coloured epoxy and the staining is permanent. Always test on an offcut. Use a translucent or stone-matched colour where possible.

Does epoxy grout need a sealer?

No. The cured epoxy is itself non-porous — sealing serves no purpose. This is one of the main advantages over cementitious grout. Some manufacturers offer a topcoat for additional chemical resistance in extreme environments (heavy commercial), but it's optional.

How long before I can shower on a new epoxy-grouted floor?

Foot traffic typically after 24 hours; full water exposure (showering, mopping with hot water) after 7 days unless the manufacturer states otherwise. Premature water exposure can cause surface tackiness and permanent dulling.

Regulations & Standards

• BS EN 13888:2009 — Grout for tiles: definitions and specifications (CG cementitious, RG reaction resin)

• BS EN 12808 parts 1–5 — Test methods for grout (compressive strength, water absorption, shrinkage)

• BS 5385-1:2018 — Code of practice for design and installation of ceramic, natural stone and mosaic wall tiling

• BS 5385-3:2014 — Code of practice for design and installation of ceramic floor tiles and mosaics

• BS 5385-4:2015 — Code of practice for tiling in special conditions (wet areas, commercial kitchens, swimming pools)

• BS 8000-11 — Code of practice for wall and floor tiling (workmanship)

• COSHH Regulations 2002 — uncured epoxy and amine hardener are skin sensitisers; nitrile gloves and arm protection required

• HSE EH40 Workplace Exposure Limits — refer to manufacturer SDS for specific hardener exposure data

• British Standards Institution — BS EN 13888 — Grout standard for ceramic tiling

• The Tile Association (TTA) — Trade body guidance on grout selection and application

• HSE — Working safely with epoxy resins — Skin sensitisation and PPE

• Mapei Technical Data Sheets — Pot life, coverage and cleaning data for Kerapoxy / Ultracolor Plus

• BAL Adhesives Technical Library — Easypoxy / epoxy grout product data

• large format tile installation — Joint widths and coverage rates for large-format porcelain

• wet room floor buildup — Wet room specification where epoxy grout is typically used

• grout repair — Cutting out failed grout for replacement

• outdoor porcelain paving tiles — External tiling where epoxy can resist freeze-thaw

• tile backer board guide — Substrate selection beneath epoxy-grouted floors