BDA Guide to Successful Brickwork

The Brick Development Association

• Publisher: Routledge
• Year: 2006
• Print ISBN: 9780750664691, 9781138174009
• eBook ISBN: 9781136426988
• Edition: 3
• Topic: Tecnologia e ingegneria
• Subtopic: Ingegneria civile

The BDA Guide to Successful Brickwork is the definitive practical guide to obtaining successful results in brickwork construction. Written by a team of experts from the Brick Development Association, the representative group in industry for brickwork construction, this best-selling text has now been brought fully in line with the latest British and European Standards, including the requirements of the new European Standard for Bricks EN771-1, to ensure readers are receiving the most up-to-date and accurate information available in the field. Based on actual teaching practice, the book is highly illustrated throughout to increase accessibility of the text for the reader in its exploration of the practical aspects of brickwork. It also includes an extensive glossary of brickwork terms for ease of reference. The third edition contains new material detailing recent innovations in brickwork, in the areas of components, systems and techniques, which includes the development of thin-joint techniques for both brickwork and blockwork. Students following NVQs and Construction Awards in Trowel Occupations (bricklaying route, at Foundation, Intermediate and Advanced level) from CITB, will find this book to be an invaluable source of information which will accompany them throughout their studies. The text has additional relevance to BTEC National and Higher Nationals in Construction, as well as GNVQ Intermediate and AVCE Construction and Built Environment courses. Building professionals concerned with the design, detailing and specification of brickwork will also find The BDA Guide to be an essential reference.

6 BACKGROUND TOPICS

This section contains articles relating to technical aspects of brickwork performance. They are intended to help the reader understand the reasons why some of the details of specification and construction exist and why it is important to comply with good practice guidance in the assembly of the work.

Also included in this section are articles on understanding drawings, the care and use of tools and the manufacture of bricks.

6.1 EFFLORESCENCE AND LIME STAINING

An understanding of the causes of efflorescence and lime staining enables bricklayers, brickwork supervisors and designers to play an appropriate part in minimising the risk of their occurrence.

DEFINITIONS

Common efflorescence is a deposit of soluble salts left on the surface of brickwork when the water in which they were dissolved evaporates (fig 6.1).⁽¹⁾

Figure 6.1 Efforescence.

Lime staining is a deposit of lime left on the face of brickwork when the water in which it was dissolved evaporates (fig 6.2).

Figure 6.2 Lime staining.

Because these two undesirable occurrences are superficially similar but have different causes and manifestations and require different actions to prevent and treat them, they are dealt with separately.

EFFLORESCENCE

The most common form of efflorescence is an unsightly but harmless white deposit which does not affect the durability of the brickwork and normally disappears from new buildings within the first few months. The very rare forms of efflorescence which may cause physical harm are beyond the scope of this section.

THE SOURCES OF SOLUBLE SALTS

Common efflorescence derives mainly from soluble salts that are contained in clay bricks and sands used for mortars but sometimes in other sources.

Clay

Salts in clay are most commonly, sulfates of sodium (Glauber’s salt), potassium (sulfate of potash), magnesium (Epsom salts) and calcium (gypsum). Ferrous sulfate is not common in clays used for brickmaking today but where it occurs it may be responsible for rusty stains on mortar or bricks (fig 6.3).

Figure 6.3 Efflorescence – a simplified diagram.

Mortar sands

Most sands come from pits or river beds and contain few salts. Sea sands contain many harmful salts and should not be used for mortars unless they have been effectively washed by a reliable supplier.

Cement

Fortunately, in Britain, Portland cement is most commonly used and its contribution to efflorescence is minimal. Some of the slag cements used abroad contain appreciable quantities of sodium sulfate which is a common cause of efflorescence and this should be considered before using such cements.

Detergents used as plasticisers

Many detergents contain sodium sulfates and should under no circumstances be used in place of properly formulated proprietary mortar plasticisers (see Section 4.1 ‘Mortars’).

Other sources

Bricks may absorb salts from ashes or the soil on which they are standing or from materials stacked or heaped in contact with them.

How efflorescence forms

Water dissolves soluble salts in the bricks and mortar and holds them in solution. As the water evaporates and the wall dries out the solution becomes more concentrated until salts begin to be deposited. This may occur out of sight within the pores of the brick or on the surface.

Exactly where, when and how much efflorescence will occur, is difficult to predict being dependent on complex chemical and physical conditions such as the type of salts, the rate of drying by wind and sun and the degree of saturation of the brickwork. The latter is the only condition which we can readily control.

Minimising the risk of efflorescence

The risk cannot be entirely avoided as it is not practicable to eliminate all salts from bricks and mortars nor keep them virtually dry, but it can be minimised by reducing the amount of water penetrating the brickwork.

Design details

Designers can use ‘umbrella’ details which protect the brickwork from saturation. Such details include effective roof verges and eaves, copings and sills to shed run-off water clear of the brickwork below (see Section 5.1 ‘Copings and cappings’). They should also avoid details which shed water on projecting plinths and other features.

Site practice

Bricklayers and site supervisors are responsible for good site practice. Bricks should be stacked clear of the ground on pallets or by other means. Mortar materials should be kept free from contamination, and bricks in stacks, on the scaffolding and newly built brickwork protected from saturation, particularly during the seven days after bricklaying (see Sections 1.2 ‘Protection of newly built brickwork’; 4.1 ‘Mortars’).

Scaffold boards adjacent to the brickwork should be turned back during rain to avoid splashing causing a band of efflorescence as well as mortar stains.

Damp conducted across mortar encrusted wall ties has been observed to cause efflorescence on internal facework.

Choice of bricks

Although BS EN 771-1 ⁽²⁾ makes provisions for the manufacture to declare the content of active water soluble salts in a brick it is important to realise that the declaration may have little, if any, correlation with the liability of the brickwork to effloresce.

Efflorescence can be avoided, or at least minimised, by appropriate design detail and good site practice as described above.

Treatment of efflorescence

It is best to allow efflorescence to weather away naturally. Do not use acid treatment, as apart from the danger to people and materials by inexpert use some salts such as vanadium may be fixed permanently. Light brushing with a bristle, never a wire, brush may be allowed.

Internal efflorescence may be treated by dissolving small patches with very little water, say a fine mist spray. The surface may then be dried with an absorbent material but, as some users have reported that this sometimes causes a blotchy appearance, it is advisable to experiment on a small inconspicuo...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Contents
• Foreword
• Training as a Bricklayer
• Glossary of Terms
• Preparation and Protection
• Bricklaying Techniques
• Good Practice
• Accessories
• Specific Constructions
• Background Topics
• Innovation
• Index