Cement for building and renovation

Cement is available in grey and white. White cement is often used where the colour of the finished product is important  – for example as a strenthening product in wall pointing mortar.

The normal building cement is ‘Artificial Portland cement’ (CPJ CEM II 42.5).

Cement should never be mixed with too much water, because this will reduce its final strength. 4 kg of cement should be mixed with up to 1 kg of water maximum (i.e. one 35 kg sack of cement should be mixed with slightly less than one bucket of water.

You can see the ‘walls’ page for a list of the differences between cement and lime when used for pointing and stonework.

Specialist cements

Specialist cements are usually sold in smaller quantities, typically 5kg. These are a very fine powder, and they contract and crack less as they dry. This makes them suitable for very fine cement and masonry work.

Uses of specialist cements (supplied by SB Mercier in DIY stores)

1. These can be used pure (3 volumes cement : 1 volume water), for very small repairs, or sprinkled on a screed floor as it dries to increase the strength of the surface.

2. Mixed with a ‘resine d’accrochage’ or simply with water (2 volumes cement : 1 volume water), to smooth the surface of an old concrete floor (although specific products are sold for this ‘ragréage’ and may be more suitable)

3. Mixed with sand and used as mortar (3 volumes cement : 6-9 volumes of sand : 1 volume of water). Again, if very small quantities are required it may be preferable to buy a sack of ready-mixed product.

Rapid drying Cement (Ciment Prompt Vicat)

This can be used for small repair work, for work that is exposed to water, and for erecting fence posts, for example, and also other work where a quick drying time is important.

Ciment Fondu Lafarge

This is a specialist cement that initially dries quickly, but doesn’t then complete its hardening any faster than normal cement. It is extremely hard when it has finished setting, so can be used, for example, for garage floors which will be subject to high wear and tear, and for wall-supporting lintels.

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