| Below are details of concrete and mortar for | | | | • For rendering walls |
| different applications, how to estimate quantities and | | | | |
| what these quantities mean. The various mixes are | | | | Sharp sand: this has a gritty feel and is similar to that |
| quoted as volume ratios, however the individual | | | | used to condition soils and potting composts, can be |
| components are normally sold by weight, so a little | | | | used for: |
| calculation work is required. | | | | |
| For normal 'around the house' types jobs, Ordinary | | | | • Concrete |
| (or Portland) cement is required. This is normally | | | | • For rendering floors and walls |
| available in 50kg bags, although smaller 25kg bags are | | | | Two types of sand are available but are not |
| increasingly becoming available to take account of the | | | | interchangeable in all applications, whichever type is |
| UK manual handling regulations. Try not to buy more | | | | being used, always pass it though a sieve before use |
| cement than you need as it cannot be stored for | | | | to remove any small stones etc. |
| very long. Some special cements are available (i.e. | | | | Aggregate (also referred to as ballast): is used for |
| quick drying) which may be required for special | | | | concrete and consists of various sized particles from |
| situation. | | | | fine grains of sand to small stones. Aggregate is |
| Lime: | | | | normally graded by size of the largest stones; 10mm |
| • hydraulic - which sets by combining with water. | | | | Aggregate will have been sieved though a 10mm |
| • Non-hydraulic - this hardens by drying out. | | | | mesh to remove all larger stones. |
| • Semi-hydraulic - which is a half-and-half, it mainly | | | | Mixes:(see bottom of page for render/stucco mixes) |
| needs to dry out but has some hydraulic properties. | | | | Mortarsand : cementsand : lime : cementgeneral |
| Each type is available as either hydrated lime and | | | | building (above ground) |
| quicklime - hydrated is more convenient to use as it | | | | 5:1 |
| has been processed ready for use. Hydrated | | | | 5:1:1general building (below ground) |
| hydraulic lime must be used straight from the bag. | | | | 3:1 |
| Hydrated semi- or non-hydraulic are better to use | | | | 6:1:1 |
| after soaking in water for 24 hours - stir it into | | | | Internal walls |
| water and leave it overnight - the lime sinks to the | | | | 8:1 |
| bottom and excess water can then be poured off. | | | | 9:2:1 |
| Mix the lime with the sand before adding the cement. | | | | |
| Lime is sometimes used in cement and reduces the | | | | Cement in concrete and mortar creates its strength |
| amount of water drawn into the bricks, thus | | | | by chemical reaction, it is not like wallpaper glue which |
| preventing the cement from drying out too quick and | | | | 'drys out', it 'goes off'. In fact, if the concrete or |
| shrinking. The main types of lime are: | | | | mortar should 'dry out' before the chemical reaction is |
| Sand: | | | | substantially complete, it will fail. Likewise if it is |
| Soft sand (or Builders sand): a smooth sand, | | | | subjected to a frost, it can also fail. |
| non-gritty, loamy and with cohesive properties, can | | | | Concrete/mortar will take months to reach it's full |
| be used for: | | | | strength however after about 24 hours it should be |
| • Bricklaying mortar | | | | fairly hard and after 4 or 5 days, the strength should |
| • For bedding paving slabs | | | | be enough to stand upto normal punishment. |