Epoxy Grout: Where It's Worth It and How to Apply It

Epoxy grout is a two-part resin grout that sets by chemical reaction rather than by drying out, so it does not soak up water, does not stain the way cement grout does, and never needs sealing. It is also harder to apply, sets on a clock, and punishes mistakes. This page explains where epoxy grout earns its extra cost and effort, where ordinary cement grout is the better choice, and how to apply it without leaving a resin film on your tiles that will not come off.

The numbers below come from the published data for two epoxy grouts sold to UK tilers, Mapei Kerapoxy CQ and UltraTile ProGrout Epoxy. Other brands differ, so always read the data sheet for the one you buy.

What epoxy grout actually is

Tile grouts sold in the UK are classified under the European standard EN 13888. It splits them into two families:

CG, cementitious grout. This is the powder you mix with water. CG1 is a normal grout and CG2 an improved one; extra letters add properties, so W means reduced water absorption and A means high abrasion resistance. A bag marked CG2WA is a good cement grout.
RG, reaction resin grout. This is epoxy. It comes as a resin and a separate hardener, and once the two are mixed a chemical reaction starts that you cannot pause.

Because a cement grout is porous, it takes in water, soap, cooking oil and dirt, which is why white grout in a shower turns grey and why most cement grouts benefit from a sealer. Epoxy has no open pores to fill. Mapei describes Kerapoxy CQ as resistant to aggressive chemicals and mould, and UltraTile sells ProGrout Epoxy as waterproof and stain resistant.

Where epoxy grout is worth it

Epoxy costs considerably more than cement grout per kilo and takes longer to lay, so it pays back only where cement grout would fail or need constant upkeep. These are the jobs where we would use it:

Shower floors and wet rooms

A level-access shower floor sits in water every day. Cement grout in that spot is the first thing to discolour, and once it starts to crumble water gets behind the tiles. Epoxy does not absorb water, so the joints stay the colour you chose. It does not replace tanking: the waterproofing still has to go on the board or screed underneath before any tiles are fixed.

Kitchen splashbacks and floors

Behind a hob, grout soaks up fat spray and turns yellow. On a kitchen floor, dropped wine, tomato sauce and coffee mark cement grout for good. Both manufacturers name kitchens as a target use for exactly this reason.

Light grout on busy floors

If you want white or pale grey joints on a hallway or kitchen floor, epoxy is the way to keep them that colour. With cement grout, pale joints on a walked-on floor are a cleaning job for life.

Pools, hot tubs and commercial kitchens

These are the jobs epoxy was made for. Mapei says basins and swimming pools grouted with Kerapoxy CQ can be filled 10 days after grouting.

Where cement grout is the better choice

Epoxy is not an upgrade for every job, and there are places where we would actively steer away from it:

Porous or textured tile faces. Unglazed natural stone, rough-finish porcelain and some handmade tiles can hold a thin film of resin in their surface. UltraTile’s own instructions say to check cleanability first, because porous or highly micro-porous surfaces may make cleaning difficult, and to test on a spare tile or a hidden area.
Floors that are not fully dry. Epoxy and porcelain together form a surface that lets no moisture out. UltraTile warns that rising moisture can build vapour pressure and loosen tiles, and says to wait 7 to 14 days on mortar beds, depending on screed thickness and conditions. A new screed needs far longer than that before it is tiled at all.
Walls in a bedroom, living room or dry hallway. Nothing there stains grout, so you pay for a benefit you will never see.
Joints wider than the product allows. ProGrout Epoxy is for 2mm to 12mm joints; Kerapoxy CQ for joints of at least 1mm. Outside those limits, pick a grout made for the width.

Epoxy grout vs cement grout at a glance

Working time: epoxy gives 30 to 40 minutes (ProGrout Epoxy) or about 45 minutes (Kerapoxy CQ) once mixed, and less on a warm day. With cement grout you can mix a small batch whenever you need it; with epoxy, a mixed kit has to be used before it sets.
Light foot traffic: about 24 hours for both epoxies above. Fast-setting cement grouts can be walked on far sooner: Ardex FL quotes 90 minutes at 20°C.
Full use: Kerapoxy CQ is ready for use after 4 days and can take chemical attack after 10. ProGrout Epoxy reaches hard set after 3 days.
Sealing: cement grout usually benefits from it; epoxy does not need it.
Repairs: cement grout can be raked out with a hand tool; set epoxy usually needs a powered tool and patience.
Colour: both come in a good spread of colours. Kerapoxy CQ is sold in 17.

How to apply epoxy grout

The process looks like cement grouting, but the timing is everything. Read the data sheet for your product and follow its mixing ratio and temperatures; the steps below are the method that works for most of them.

Rubber grout float with a white handle — A rubber grout float, the tool used to press grout into tile joints | Fugenbrett by Goele (Public domain), via Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Fugenbrett.png

1. Prepare the joints

Let the tile adhesive cure for the time its own data sheet gives. Rake out any adhesive in the joints, even if it has hardened, and vacuum the dust out. UltraTile asks for joints of even depth across the whole area, because thin spots are where chemical resistance fails. The tile surface must be dry and clean, and the room within the product’s temperature range: 5°C to 30°C for ProGrout Epoxy.

2. Mix the whole kit, or weigh it

The resin and hardener are packed in the right ratio. If you mix only part of a kit by eye, you risk grout that stays soft or turns brittle. Either mix a whole unit or split it accurately by weight on scales. Mix slowly with a paddle on a low-speed drill until the colour is even all the way through, scraping the sides of the tub.

3. Work in small areas

Spread the grout with a hard rubber epoxy float, pressing it diagonally across the joints so they fill fully. Mapei specifies a rubber trowel and a cellulose sponge for Kerapoxy CQ. Do about a square metre, then clean that square before moving on. Leaving a whole wall to clean at the end is how resin film gets left behind.

4. Clean off while the grout is still soft

Hold the float edge-on and scrape off as much excess as you can. Then go over the area with clean water and a scouring pad or sponge to loosen the residue, and wipe it away with a well-wrung sponge. Change the water often: dirty water simply spreads a thinner layer of resin across the tile. Finish with a final light wipe, working diagonally so you do not drag grout out of the joints.

5. Leave it alone

Keep people off the floor for the 24 hours both products quote for light foot traffic, and do not use the shower or fill a bath against fresh grout until the product says it is fully cured. Cold rooms slow the cure; in winter, give it longer.

Fixing epoxy residue and haze

If you see a sticky sheen or a dull film on the tiles the next day, cleaning was too slow or the water too dirty. Ordinary grout haze remover made for cement grout will not touch set epoxy. Use a remover made for resin, such as UltraTile ProClean Epoxy Resin-Off, and test it on a hidden tile first. For cement grout haze, our page on how to remove grout haze covers which cleaner suits which grout.

Prevention is far easier than removal. On a first epoxy job, grout a small, out-of-sight area first to learn how fast the product stiffens in your room.

Corners, edges and movement joints

Epoxy is hard and rigid. It still does not belong in internal corners, where a wall meets a floor, around a bath or shower tray, or in movement joints across large floors. Those joints move, and any rigid grout will crack there. Fill them with a flexible sanitary silicone instead, after the grout has cured.

Can you put epoxy grout over old grout?

Not as a thin skim. Epoxy needs depth and an even joint to bond and to resist water. To switch a tired shower from cement grout to epoxy, rake out the old grout to a consistent depth, vacuum the joints, let everything dry fully and then grout as above. If the old grout is only cracked in a few places, our guide to cracked grout repair may be the cheaper fix.

For the full cement grouting method, see how to grout tiles, and for help choosing a shade, choosing a grout colour. For full technical data, read the UltraTile ProGrout Epoxy product page. If you would rather a tiler handled an epoxy job in Bromley or south east London, Bromley Tilers can quote for it.

Frequently asked questions

Is epoxy grout worth it?

Yes in showers, wet rooms, kitchens, pale-grouted floors and pools, where cement grout stains or breaks down. In dry rooms there is little to gain, and cement grout is cheaper and much easier to lay.

Does epoxy grout need sealing?

No. It is non-porous once cured, so there is nothing for a sealer to fill. Cement grout is the type that usually benefits from a sealer.

How long does epoxy grout take to dry?

It cures rather than dries. Both Kerapoxy CQ and ProGrout Epoxy take light foot traffic after about 24 hours. ProGrout Epoxy reaches hard set in 3 days, and Kerapoxy CQ is ready for use after 4 days and resists chemicals after 10. Cold rooms take longer.

Can a beginner use epoxy grout?

Yes, on a small area, if you mix the full kit, work a square metre at a time and clean as you go. The usual beginner mistake is grouting a whole wall before cleaning, which leaves a resin film that is very hard to remove.

Can you use epoxy grout on natural stone?

Sometimes. Polished, dense stone can take it, but porous or textured stone can trap resin in the surface. Test the grout and your cleaning method on a spare tile before you start.

What is the difference between CG2 and RG grout?

Both are EN 13888 classes. CG2 is an improved cementitious grout mixed with water. RG is a reaction resin grout, which in practice means epoxy.

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Epoxy Grout: Where It’s Worth It and How to Apply It