CG1 versus CG2: what the classes actually mean
European standard EN 13888 splits cementitious grout into CG1 (basic) and CG2 (improved, meaning higher abrasion resistance and lower water absorption). For bathrooms and kitchens we specify CG2 as standard; the extra cost over CG1 is a few pounds a bag and it pays back in stain resistance within the first year.
Within CG2 there are further suffixes: W for reduced water absorption and A for enhanced abrasion resistance. A CG2WA grout on a shower floor is genuinely a different animal to a basic sanded grout in a hallway.
Wide-joint work (10mm plus, common with rustic or handmade tiles) usually needs a specific wide-joint or 'flexible' formulation rather than a standard sanded grout, because shrinkage cracking becomes far more visible over a bigger cross-section.
Epoxy grout: when it earns its keep
Epoxy grout (resin and hardener rather than cement) is virtually non-porous, chemically resistant and does not need sealing. It is the right call for shower floors, wetroom trays, kitchen splashbacks that see grease, and any commercial-style finish where stain resistance matters more than budget.
It is also considerably harder to apply. Working time is short, it needs cleaning off the tile face before it cures, and haze removal on textured tiles can be genuinely difficult. We price epoxy grouting as a separate line because it takes noticeably longer per square metre than cementitious grout.
A sensible middle ground on a lot of bathrooms: epoxy in the shower enclosure and around the bath upstand, standard CG2 elsewhere. It targets the spend where the wet exposure is highest.
Choosing joint width by tile format
Joint width is not a style choice alone; it is set largely by the calibration tolerance of the tile. A pressed rectified porcelain tile can run a 2mm joint because every piece is nearly identical in size. A handmade Moroccan zellige tile with a plus or minus 3mm size variation simply will not lay flat with anything narrower than 5mm or 6mm.
| Tile type | Recommended joint | Notes |
|---|---|---|
| Rectified porcelain, large format | 1.5mm-3mm | Minimal joint for a clean, near-seamless look |
| Standard ceramic wall tile | 2mm-3mm | Manufacturer's calibration tolerance sets the minimum |
| Metro/subway tile | 2mm-3mm | Wider joints exaggerate the bevel edge unnecessarily |
| Natural stone | 3mm-5mm | Wider joint accommodates size variation between pieces |
| Handmade/artisan tile | 4mm-8mm | Irregular edges need the extra tolerance |
Grout colour: practical advice, not just Pinterest
Light grout on a light tile shows every hairline of dirt build-up within a couple of years, especially on a shower floor. Mid-grey and anthracite tones hide day-to-day soiling far better and remain popular for exactly that reason.
Matching grout to tile colour gives a calm, seamless wall; contrasting grout (dark grout, light metro tile, for example) gives definition to the pattern but shows any inconsistency in joint width mercilessly, so it demands tighter setting-out.
Test a sample on an offcut before committing on a large area. Grout colour changes visibly once sealed and again once fully cured, so what comes out of the bucket is not the final colour.
Sealing: where it matters and where it does not
Cementitious grout in a wet area benefits from an impregnating sealer, reapplied roughly every 12 to 24 months depending on exposure. It slows staining; it does not make the grout waterproof, which is a common misconception.
Movement joints (where tile meets bath, tray, worktop or an internal corner) should always be silicone, never grout, because rigid grout will crack as the substrate moves. A colour-matched sanitary silicone with fungicide is the correct product here.
External corners on floor tiling in wetrooms also want a movement joint rather than a grouted arris, for the same reason.
Keeping grout looking new
A daily squeegee after showering removes most of the standing water that carries limescale and soap residue into the joint.
Weekly cleaning with a pH-neutral bathroom cleaner is enough for CG2 grout that has been sealed. Bleach-based products used constantly will eventually strip a sealer and dull coloured grout.
For established grey or black staining, a proprietary grout whitener or a diluted oxygen-based cleaner with a stiff (not wire) brush usually restores colour without damaging the joint; a steam cleaner is a good middle step before considering regrouting.
If joints are cracking, crumbling or pulling away from the tile edge, that is a sign of movement or a poor original mix rather than a cleaning problem, and it is worth having it looked at before water gets behind the tiling.
Where to read next
Questions we get asked most
Do I need epoxy grout throughout the whole bathroom?
Not usually. We tend to recommend epoxy in the shower enclosure and around the bath, where standing water and cleaning chemicals are most concentrated, and a good CG2 cementitious grout elsewhere.
Why does my grout keep going black in the corners?
That is almost always mould feeding on soap film and moisture rather than a fault with the grout itself. Better ventilation, a daily squeegee and periodic cleaning usually resolve it; recurring black mould right at a corner often points to a missing or failed silicone movement joint behind it.
Can grout colour be changed later without retiling?
Yes, within reason. Existing grout can be raked out to a suitable depth and regrouted in a new colour, or a grout paint/refresh product can be used for a lighter-touch update, though it will not last as long as fresh grout.
What width joint do you recommend for a large-format porcelain floor?
For rectified porcelain we typically run 2mm to 3mm. Anything tighter risks lippage becoming visible; anything much wider looks unintentional on a tile designed for a minimal joint.
Is sanded grout the same as CG2?
Not necessarily. 'Sanded' just describes the aggregate added for wider joints. It can be a CG1 or CG2 formulation, so it is the class rating rather than the word 'sanded' that tells you the performance.