Concrete Mixes and Building Mortars

Cement in concrete and mortar creates its strength by chemical reaction, it is not like wallpaper glue which 'drys out', it “goes off”. In fact, if the concrete or mortar should “dry out” before the chemical reaction is substantially complete, it will fail. Likewise if it is subjected to a frost, it can also fail.

Concrete/mortar will take months to reach it's full strength however after about 24 hours it should be fairly hard and after 4 or 5 days, the strength should be enough to stand up to normal punishment.

The various components:

Cement: For normal 'around the house' types jobs, Ordinary (or Portland) cement is required. This is normally available in 50kg bags, although smaller 25kg bags are increasingly becoming available to take account of the UK manual handling regulations. Try not to buy more cement than you need as it cannot be stored for very long. Some special cements are available (i.e. quick drying) which may be required for special situation.

Lime: Lime is sometimes used in cement and reduces the amount of water drawn into the bricks, thus preventing the cement from drying out too quick and shrinking. The main types of lime are:

· hydraulic - which sets by combining with water.

· Non-hydraulic - this hardens by drying out.

· Semi-hydraulic - which is a half-and-half, it mainly needs to dry out but has some hydraulic properties.

Sand: Two types of sand are available but are not interchangeable in all applications, whichever type is being used, always pass it though a sieve before use to remove any small stones etc.

Gravel: consists of various sized small stones and is mixed with sharp sand for concrete (instead of using aggregate/ballest). Gravel is normally graded by size of the largest stones; 10mm gravel will have been sieved though a 10mm mesh to remove all larger stones.

Aggregate (also referred to as ballast): is used for concrete and consists of various sized particles from fine grains of sand to small stones(gravel). Aggregate is normally graded by size of the largest stones; 10mm Aggregate will have been sieved though a 10 mm mesh to remove all larger stones.

The Building Materials and Structures Integrated Plant of Ahangarancement offers high-quality concrete and mortar of the following types: