Build Masonry

CONCRETE

Constructing Durable Masonry

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SCOPE IMPORTANT SAFETY INFORMATION When handling and using cement or fresh concrete, avoid skin contact. Wear suitable protective clothing.

This data sheet sets out practices to be followed when constructing masonry to ensure the durability of the resulting wall. For guidance on checking the plans and specification to see that all required information is included and that appropriate materials have been specified see Concrete Data ‘Durable Masonry Specification Checklist’. INTRODUCTION

Cement and Concrete Association of Australia The Association is a non-profit organisation sponsored by the cement industry in Australia to provide information on the many uses of cement and concrete. This Guide is distributed by the Association for that purpose. Since the information provided is intended for general guidance only and in no way replaces the services of professional consultants on particular projects, no legal liability can be accepted by the Association for its use. JULY 1999 B2 Page 1 of 2

Although the process of ensuring masonry elements are durable and don’t suffer deterioration during their life begins at the design and specification stages, it is the construction phase that is crucial to achieving the objective. This data sheet outlines the steps that should be followed during construction to produce durable masonry.

STORAGE OF MATERIALS ON SITE Generally, materials should be ordered and supplied so they are incorporated into the structure as soon as possible after delivery. Long storage periods should be avoided. Materials should be stored on site so as to prevent deterioration or contamination. Particular requirements for some materials include:

ORDERING MATERIALS

Cement and Lime Store in bags off the ground in a dry environment, eg waterproof shed. Minimise air circulation around bags. Keep different Types of cement, eg Type GP (General purpose portland) and Type GB (General purpose blended) in separate stacks so they are not used interchangeably. Use on a ‘first-in/first-out’ basis.

Orders for materials should comply with the requirements as set out in the plans and specification. When placing orders, ensure that the supplier attaches any required test certificates and documentation to confirm that the specified material has been supplied.

Masonry units Masonry units should be stored on pallets in the wrapping as delivered from the manufacturer. When the units are taken from the pallet they should be stacked off the ground on a clean, firm surface. Reinforcement Reinforcement should be stored off the ground and supported at sufficient points along its length to avoid bending or distorting the bars. It should be protected from contamination by oil, paint or other coatings that can reduce the bond.

CONCRETE

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Cement and Concrete Association of Australia Page 2 of 2

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MIXING MORTAR ■

Batch by volume Ingredients should be measured accurately by volume. Volume batching does not mean by ‘shovelful’ as a shovelful of cement and a shovelful of sand (usually damp) are not equal in volume.

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Use only specified materials Don’t add ‘fire clay’ or ‘brickies loam’ to the mix. These reduce the bond of the mortar.

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Do not use additives to replace lime Lime makes the mortar creamier and easier to use, improves bond and minimises cracking.

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Beware of overdosing with admixtures Chemical admixtures have their place but must be used with care. It is not true in this case that more is better. Overdosing will lead to a dramatic loss of bond and resulting poor performance of the masonry.

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Mix in a mechanical mixer Mortar should be mixed in a tilting drum or a ‘cement-mixer’. Hand mixing, eg in a wheelbarrow, should be used only in special circumstances.

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Adding materials to mixer A small amount of mixing water is placed in the mixer followed by the sand, cement and lime. More water is then slowly added to create a thick creamy mortar.

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Mix for a sufficient period of time Each batch should be mixed for two to three minutes to ensure a uniform distribution of materials.

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Use promptly Mortars should be used within half an hour of mixing. Do not add water to mortar which has stiffened to restore workability as this will reduce the quality of the mortar and impair the masonry performance.

LAYING UNITS Units must be laid in the specified bonding pattern with the appropriate bedding. Solid and cored units are laid on full bedding and hollow units on face-shell bedding. Vertical joints in fully-bedded masonry should be completely filled with mortar. Check the specification for face-shell bedded masonry. Mortar joints should be tooled to give a dense, water-shedding surface. Joints should not be raked in other than mild environments. Note that AS 3700 lists a number of restrictions when raking joints, for example stipulating that joints in hollow-unit, ungrouted masonry must not be raked. WALL TIES AND OTHER COMPONENTS Wall ties and other components should be incorporated into the construction as specified and, if appropriate, in accordance with the manufacturer’s instructions. Ensure that wall ties are properly bedded and fixed to supporting members. PROTECTION OF NEWLY-LAID MASONRY Newly-laid masonry should be protected from rain by covering the top of the construction with plastic sheeting. Mortar joints should be protected from premature drying out by wrapping the masonry in plastic sheeting and shading the walls where possible.

Do not add water to mortar which has stiffened to restore workability as this will reduce the quality of the mortar and impair the masonry performance.