Joint width isn't just an aesthetic decision: it changes the real consumption of material and, in damp areas, the type of grout needed so it doesn't fill with mould within a few months.
Joint width by tile format
- Narrow joint (1.5–2 mm): on large-format rectified porcelain, for an almost continuous look.
- Wide joint (5–8 mm): on rustic or irregular tiles, where a thin joint would leave the size differences between tiles very visible.
How consumption is calculated
Cement grout consumption depends directly on the joint width chosen and the tiled area:
Consumption (kg) = Area (m²) × Joint width (mm) × 0.15
Worked example: for 10 m² tiled with a 3 mm joint: 10 × 3 × 0.15 = 4.5 kg, rounded up to 1 bag of 5 kg. This is the same calculation the PresupuestoYa calculator applies automatically for the Tiler trade.
When to use epoxy grout instead of cement
Epoxy grout, two-component, waterproof and highly resistant to stains and chemicals, is common in commercial kitchens, heavily used showers or swimming pools. It is more expensive and more laborious to clean off fresh than cement grout —the excess has to be removed with a sponge and water before it hardens— but it needs no water-repellent treatment afterwards as cement grout does.
In heavily used showers, commercial kitchens or swimming pools, epoxy grout holds up much better than cement, even though it is more expensive — it's worth explaining to the client why it costs more in those particular cases.
Sanitary silicone: always with fungicide in damp areas
In corners and junctions (bath–wall, floor–wall), where a rigid cement joint would crack at the slightest movement, flexible silicone is used. Always use silicone with fungicide in damp areas: without it, the joint in the shower or bath collects black mould within a few months, especially in white or light-coloured silicones.
Frequently asked questions
How much cement grout do I need for 15 m² with a 2 mm joint? 15 × 2 × 0.15 = 4.5 kg, rounded up to 1 bag of 5 kg.
Why doesn't epoxy grout need water-repellent treatment and cement grout does? Because epoxy is already waterproof by its own two-component composition, whereas cement grout is porous and needs an additional treatment to resist water.
What happens if I use silicone without fungicide in the shower? It collects black mould within a few months, especially in white or light tones — always use sanitary silicone with fungicide in those areas.
Conclusion
Calculating the grout from the real width chosen, not a generic figure, and using epoxy in the most demanding areas (swimming pools, heavily used showers, commercial kitchens) is what makes the grouting last over time. Silicone with fungicide in the corners completes a finish that doesn't fill with mould soon after it's done.
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