Bonding

Figure 1.12 illustrates the effects of bonding. The stretcher bond is standard for cavity walls and normally a half-lap bond is used, but an increase in horizontal emphasis can be achieved by the less standard quarter or third bond. In conservation work it may be necessary to use half bricks (snap headers) to match the appearance of bonding in solid brick walls. For one-brick-thick walls more variations are possible; most typical are the English and Flemish bonds. The equivalent English and Flemish garden wall bonds, which have more stretchers, are primarily used for one-brick-thick walls where the reduced number of headers makes it easier to build both sides fairfaced. Panels of herringbone brickwork (raking bond), or dog tooth and dentil courses as in Victorian brickwork, can generate interesting features.

In all cavity brickwork, wall ties manufactured from galvanised steel, stainless steel or polypropylene to BS EN 845-1: 2003 should be incorporated (Fig. 1.13). They should be laid drip down and level or sloping down towards the outer leaf. Where mortar bed-joints do not co-ordinate between masonry leaves, slope-tolerant cavity wall ties must be used. In

Table 1.4 Mortar mix designations

Designation

Cement:lime:

Masonry cement:

Cement:sand

sand

sand

with plasticiser

(i)

1:0:3 - 1:/:3

(ii)

1:/:4 - 1:/:4 /

1:2/- 1:3/

1:3 - 1:4

(iii)

1:1:5 - 1:1:6

1:4 - 1:5

1:5 - 1:6

(iv)

1:2:8 - 1:2:9

1:5/ - 1:6/

1:7 - 1:8

(v)

1:3:10 - 1:3:12

1:6/- 1:7

1:8

partially filled cavities, the wall ties should clip the insulation cavity batts to the inner leaf. In all cases the cavity, insulation and ties should be kept clear ofmor-tar droppings and other residues by using a protective board. With the widening of cavities associated with increased insulation, the use of the traditional butterfly, double triangle and vertical twist ties in galvanised steel will be increasingly replaced by longer stainless steel ties, which do not suffer from corrosion in the more aggressive environments. Asymmetric wall ties are used for fixing masonry to timber or thin-joint aircrete blockwork. Movement-tolerant wall ties bend, or slide within a slot system fixed to one leaf of the masonry.

Fig. 1.13 Wall ties

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Homeowners Guide To Landscaping

Homeowners Guide To Landscaping

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