Plasticiser Dry silo mixer A major piece of equipment that contains all the dry materials to produce mortar mixed on demand Take care around the moving parts of drum mixers! They are powerful machines and need to be treated with respect. Dry silo mixer Drum mixer Ready mix arriving on a site An operative mixing by hand There will still be occasions when there will be a need to mix mortar by hand for smaller jobs. For example, a small garden wall may be difficult to access with machinery such as a mixer, so mixing by hand will be the only option. Whatever method is used to mix mortar, always keep in mind the hazards associated with the materials used. These are covered in more detail in Chapter 1, but when preparing and placing mixing materials prior to building brickwork, remember that cement and lime powders can irritate your skin and aggregates Research the health effects of irritation are heavy to move especially when wet. from cement and lime dust. Find out what diseases can be caused.

Once fretting has begun it will not stop until the salt source is identified and removed. It could then take another 12-24 months before the fretting process comes to a complete halt. Once the fretting process has stopped the brickwork can then be repaired. Any repairs made to the brickwork while the fretting action is still occurring will generally fail. Fretting brickwork may be treated using breathable sealers that penetrate the brickwork and consolidate loose particles. However, depending on the degree of fretting it may be necessary to replace the affected brickwork. Figure 3 Effect of salt attack on brickwork Brick Properties Brick Technical Manual 9 1.5 Expansion Brick Growth Bricks undergo long-term permanent expansion over time. This expansion continues for the life of the brick, but the majority of the growth occurs early in its life. Most bricks have a coefficient of expansion in the range of 0.5-1.5mm/m (millimetres per metre) over fifteen years. Designers can use the values of the coefficient of expansion to accommodate for the growth of bricks by the size and spacing of the control joints.

CH Inorganic clays of high plasticity, fat clays, silty clays, etc. Poor to fair Medium OH Organic silts and organic clays of high plasticity Poor to very poor Medium Peat Highly organic PT Peat and other highly organic soils Not suitable Slight TABLE 6.20 Characterics of Compacted Subgrade for Roads and Airfields (from The Unified Soil Classification System, U.S. Army, 1960) (Continued) Compressibility Drainage properties Compaction equipment Typical dry densities pcf Mg/m3 Sub. mod.,a pci Almost none Excellent Crawler-type tractor, rubber-tired roller, steel-wheeled roller Almost none Excellent Crawler-type tractor, rubber-tired roller, steel-wheeled roller Very slight to slight Fair to very poor Rubber-tired roller, sheepsfoot roller 115145 1.842.32 2060 200500 Slight Poor to very poor Rubber-tired roller, sheepsfoot roller 130145 2.082.32 2040 200500 Almost none Excellent Crawler-type tractor, rubber-tired roller 110130 1.762.08 2040 200400 Almost none Excellent Crawler-type tractor, rubber-tired roller 105135 1.682.16 1040 150400 Very slight to medium Fair to poor Rubber-tired roller, sheepsfoot roller 100135 1.602.16 1040 100400 Slight to medium Poor to very poor Rubber-tired roller, sheepsfoot roller 100135 1.602.16 520 100300 Slight to medium Fair to poor Rubber-tired roller, sheepsfoot roller 90130 1.442.08 15 or less 100200 Medium Practically impervious Rubber-tired roller, sheepsfoot roller 90130 1.442.08 15 or less 50150 Medium to high Poor Rubber-tired roller, sheepsfoot roller 90105 1.441.68 5 or less 50100 High Fair to poor Sheepsfoot roller, rubber-tired roller 80105 1.281.68 10 or less 50100 High Practically impervious Sheepsfoot roller, rubber-tired roller 90115 1.441.84 15 or less 50150 High Practically impervious Sheepsfoot roller, rubber-tired roller 80110 1.281.76 5 or less 25100 Very high Fair to poor Compaction not practical Source: U.S. Army, The Unified Soil Classification System.