1.3 Brick Masonry Construction
Bricks & Pavers Technical Manual
1.301
Section 1.3. Brick Masonry Construction
The following information relates to the construction of brick walls to meet AS3700, the design and aesthetic
requirements.
Mortar
AS3700: 2001, Table 10.1 gives the options for mortar mixes classified as M1 to M4. M1 mortars are for
restoration applications. M2 mortars are for use in interior walls above dampcourse or in exterior walls above
dampcourse if more than one km from a body of salt water and 10 km from a surf coast and the wall has
protection from water ingress above. M3 and M4 mortars are those most commonly used in construction. Table
11 gives the proportions of the most commonly used mortars. Other deemed-to-satisfy compositions are given in
AS3700. Special mortars that are tested and shown to meet requirements are allowed with verification on site.
Note: Proportions are by volume and should be measured with a bucket or gauge box, NOT A SHOVEL.
Table 11. Typical Mortar Mixes
Mix proportions by volume
Portland or
Hydrated
Blended Cement
Lime
Sand
Mortar
Type
Durability
Class
M1
PRO
0
1
3
No
M2
PRO
1
2
9
No
M3
GP
1
1
6
No
M3
GP
1
0
5
Yes
M4
EXP
1
1
⁄2
41⁄2
No
M4
EXP
1
0
4
Yes
Water
Thickener*
Refer to page 1.104 for description of Durability Class. *Methylcellulose type, not air entrainers such as detergent.
Where masonry strength is crucial, trial walls should be constructed with the bricks and mortar to be used on
the job, then tested before construction commences. Masonry bond strength is related to the suction of the
bricks, the particle size distribution of the sand, cement content, additive contents, etc. For many jobs these
panels can also be used as physical samples of the required quality of the bricklaying and cleaning.
Note: AS 3700 allows the use of:
•
Cements complying with AS 3972 or AS 1316
•
Lime complying with AS 1672.1
•
Sand that is free of any deleterious materials
•
Water that is free from deleterious materials and
•
Admixtures including plasticisers, air entraining agents and set retarders complying with AS1478.1,
cellulose-type water thickeners, colouring pigments complying with BS EN 12878 and bonding polymers. t
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Bricks & Pavers Technical Manual
1.302
Section 1.3. Brick Masonry Construction
Mortar (continued)
No other material may be used until tests on masonry constructed with the mortar, made with the material or
admixture shows the masonry complies with the standard’s requirements for compressive strength, flexural
strength and durability.
Deleterious materials are those reducing the strength or durability of the masonry and including anything that
attacks the built-in components. This means the use of fire clay, detergent, sugar, soft drink, etc., are banned.
Most of these materials severely reduce mortar strength and durability. Water thickener must be used only
according to the manufacturer’s directions because overuse severely reduces mortar strength.
Mortar Estimator
Table 12. Estimated Material Requirements to Lay 1,000 Standard Bricks
Mix
Composition
(C:L:S)
40 kg bags
of cement
25 kg bags
of lime
Cubic metres
of sand
Tonnes of
damp sand
M3
1:1:6
4
2.4
0.64
1.2
M3
1:0:5
4
0
0.64
1.2
M4
1:0:4
6.5
0
0.64
1.2
M4
1 : 1⁄2 : 41⁄2
5.3
1.6
0.64
1.2
This table assumes partial filling of cores and typical site wastage.
Only make sufficient mortar for immediate use. If mortar starts to set, it may be re-tempered once only.
Where bricklaying is interrupted, the mortar should be covered to prevent evaporation and mixed with the trowel
before continuing. t
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Bricks & Pavers Technical Manual
1.303
Section 1.3. Brick Masonry Construction
Mortar (continued)
Mortar Colour
The mortar colour can dramatically affect the overall look. The colour of mortar is influenced by the colour of the
cement and the aggregates (sand). Many pigments are also available ranging in colour through red, yellow,
brown, green, blue and black (mainly oxides but carbon black can be used to give black mortar). The cheapest
way of colouring mortar is to use coloured sand. White and yellow sands are commonly available but red and
brown sands are also available. Sands are normally natural materials which vary considerably even in the one
deposit. To ensure colour consistency, sufficient sand from the one batch should be set aside for the whole job.
Where colour is crucial to the look of the masonry, before accepting the sand, a trial wall should be built (4 bricks
x 10 courses). After the mortar dries assess the colour. Where oxides or carbon black are used as colours never
use more than 10% by weight of the cement content.
Colours are additive in their effect and it is possible to get different shades and tones of mortar using different
combinations of cement, sands and oxides.
Table 13: Typical Coloured Mortar Components
Mortar Colour
Cement
Sand
Oxide
Red
Grey
White or Yellow or Red
Red
Yellow
Off-white or Grey
Yellow
Yellow & Brown
Cream
Off-white
Yellow
None
Tan
Grey
White or Yellow
Brown
Black
Grey
Yellow
Black
Note: The colour of mortar can be severely degraded by incorrect or poor brick cleaning. ■
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Bricks & Pavers Technical Manual
1.304
Section 1.3. Brick Masonry Construction
Joint Types
The type of joint can dramatically affect the overall look of brick masonry. Joints can be used to create a casual,
rustic or formal look to brickwork. There are many different joints; the most common ones used in Australia are
shown below.
Flush Joint
Raked Joint
Ironed Joint
Struck Joint
Weathered Joint
Terminology and joint preference differs in different countries and within Australia. Where there is any
confusion, always use a drawing or physical sample to avoid misunderstandings.
Shallow ironed joints are recommended in areas requiring exposure grade bricks and mortar. Tooling the joint to
produce ironed and struck joints is equivalent to steel trowelling concrete and produces a dense smooth surface
which sheds water and dirt better than other types of joint. Ironed and struck joints should always be used for
bricks with straight sharp edges such as Smooth Face and Velour bricks.
Raked joints may be used with any type of brick but they tend to retain dirt and may lead to streaks down the
masonry in dirty environments. Raking must not come closer than 5 mm to any core. This usually limits raking to
less than 10 mm, however it is best to check the bricks that are being used before raking. AS3700 specifies that
joints in walls in marine, severe marine or aggressive environments or on aggressive soils must be tooled to a
dense smooth surface. This precludes raking and in practice ironed joints are the only ones that consistently
meet the requirement.
Flush joints may be used with any type of brick. However, flush joints are particularly effective with rumbled
bricks as flush joints make the joints look to be of variable thickness that gives a pleasing rustic look. ■
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Bricks & Pavers Technical Manual
Section 1.3. Brick Masonry Construction
1.305
Joint Sizes
Mortar bed joints are required to be less than 10 mm unless the design specifies another thickness. A different
thickness may only be specified after the designer considers the effect on compressive and flexural strength of
the masonry. During construction mortar bed joints are allowed to deviate by ± 3mm. Because of poor practice
or lack of proper direction some slabs and footings are finished at the wrong height. Mortar joints up to 50 mm
thick have been used to get the correct coursing, however, this is not allowed under AS3700.
Perpends are to have a minimum design thickness of 5 mm. In structural brickwork perpends may be up to 10 mm
thicker than the specified thickness but no thinner. In face brickwork perpends may deviate by ± 5 mm from the
average width but in any one wall the maximum difference allowable between any two perpends is 8 mm.
The preceding tolerances do not apply in the case of thin bed mortars and perpend tolerances do not apply where
perpends are not filled with mortar. ■
Weepholes
Weepholes are to allow moisture that collects in the cavity to escape. Weepholes should be spaced at less than
1200 mm centres wherever flashing is built into the masonry to shed water from the cavity. Weepholes are
usually empty perpends (10 mm wide) but proprietary products are available to prevent the entry of insects. In
high wind areas it has been known for water to be blown up the cavity onto the inner wall and as this is very
undesirable, more, narrower weepholes are usually built into the wall. It is essential that weepholes remain open
and render and other applied coatings, where used, must be raked out of the joint. ■
ADV03787
Bricks & Pavers Technical Manual
Section 1.3. Brick Masonry Construction
1.306
Brick Estimator
Brickwork is based on the 600 mm unit, (seven courses high and two and a half bricks long). This unit fits in with
doors, windows and other building materials. The number of bricks required for a wall can be determined from
the Brick Coursing Height and Brick Gauge tables on pages 1.310-1.312 of this manual. Select the height of the
wall and from the following page for the brick height chosen determine the number of courses. From the next
page for 230 mm long bricks or the one after for 290 mm bricks, determine the number of bricks for the length of
your wall. A half brick should be calculated as 1 whole brick, due to site wastage. Multiply the number of bricks
by the number of courses to give the number of bricks for the wall. Saw cutting bricks may mean getting two
halves from a brick but this is not usual practice because of the cost of cutting. ■
ADV03788
Bricks & Pavers Technical Manual
Section 1.3. Brick Masonry Construction
1.307
Brick bonds and other decorative effects
A bond is the pattern in which bricks are laid. The most common bond is Stretcher Bond which consists of courses
of full bricks where every course is offset half a brick from the course below. When following the mortar joint,
stretcher bond has the longest vertical pathway and therefore the best bend strength.
Stretcher bond is used in walls one brick wide. Where walls are two or more bricks wide then stretcher bond
needs ties to hold the leaves together to give it a monolithic action. To avoid the use of ties traditional practice
has been to lay some of the bricks sideways. This has usually been either full courses of headers with full
courses of stretcher (English) or courses of alternating header and stretcher (Flemish). A variation of Flemish
Bond is Garden Wall Bond where courses are made of a header and three stretchers alternating.
Corner treatment can be different in these bonds. English corners end in full stretchers or full headers, and any
part brick required to make up the course is set inside the corner. Dutch corners end in the part bricks.
Variations on these bonds are common in particular a header course every three or six courses with stretcher
courses between.
Although these bonds have traditionally been developed for thick walls, they can be used in single leaf walls as
a decorative effect using cut bricks for the headers. Such walls are usually non-load bearing. Cutting costs are
high but not excessive as the headers have the cut side turned in and the bricks can be bolstered.
Other decorative bonds may be used in non-load bearing applications, particularly in the form of panels. The
limitations are strengths lower than Stretcher Bond and the cost of cutting and slower brick laying. The
decorative effect of bonds is highlighted by using a mortar in a contrasting colour to the brick.
Other bonds include:
•
Stack Bond – Bricks laid horizontally in vertical columns so all vertical joints align.
•
Soldier Stack Bond – Bricks laid vertically in vertical columns so all vertical joints align.
•
1/3 Bond – Every course is offset by 1/3 of a brick.
•
Zigzag Bond, Vertical Zigzag Bond, 45˚ Stretcher Bond, Chevron Bond, Basket Weave Bond, 45˚ Basket
Weave Bond and virtually any pattern that tessellates. t
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Bricks & Pavers Technical Manual
Section 1.3. Brick Masonry Construction
1.308
Brick bonds and other decorative effects (continued)
Other decorative effects are available such as:
•
Laying bands of bricks of the same colour with different textures eg smooth faced and rock faced;
•
Laying bands of bricks with different (contrasting or complimentary) colours;
•
Corbelling (bricks set out from the wall);
•
Racking (bricks set back into the wall);
•
Quoining (corner bricks in different colours or set out from the wall);
•
Soldiers above openings or as a single course;
•
Copings on piers and parapet walls;
•
Sills in different colours or textures, using sill bricks, etc.; or,
In the late 1800’s bricks of contrasting colours were laid in patterns such as diamonds or crosses. A more subtle
effect can be made by laying bricks with different textures or corbelling the bricks in these patterns.
Combinations of the above effects can be used. Eg. An American Architect specified a corbelled course with the
course below to be laid in the darkest bricks selected from the packs delivered. The darker band accentuated the
shadowing effect from the corbelled course. t
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Bricks & Pavers Technical Manual
1.309
Section 1.3. Brick Masonry Construction
Brick bonds and other decorative effects (continued)
Stretcher Bond
Common Bond (Full Headers every 6th Course)
Flemish Bond
Common Bond (Flemish every 6th Course)
English Cross or Dutch Bond
Garden Wall Bond
Stack Bond
Soldier Course (With Stretcher Bond)
ADV03791
Bricks & Pavers Technical Manual
1.310
Section 1.3. Brick Masonry Construction
Brick Coursing Height
3000
36
24
18
35
49
34
23
2700
48
17
33
31
21
16
44
43
15
29
41
14
27
18
13
16
22
33
12
23
11
20
1500
28
13
10
9
24
23
1200
11
10
21
19
9
7
8
18
16
6
11
10
13
5
6
5
4
8
4
3
5
17
16
1500mm
15
14
13
1200mm
12
11
3
2
4
3
2
900mm
9
8
7
600mm
6
5
4
5
2
3
10
7
6
4
18
10
9
6
300
1800mm
12
11
8
7
19
15
14
7
9
600
20
17
12
900
21
20
14
13
2100mm
22
8
15
22
25
12
16
23
27
26
18
17
24
30
29
14
19
2400mm
32
31
15
21
25
35
34
24
1800
38
36
17
26
37
26
25
2700mm
27
40
19
39
2100
28
42
20
28
29
45
30
2400
30
47
46
22
32
3000mm
50
300mm
3
2
2
1
1
1
1
1
76mm
119mm
162mm
50mm
90mm
ADV03792
Bricks & Pavers Technical Manual
1.311
Section 1.3. Brick Masonry Construction
Brick Gauge
230 mm Long Bricks
No. of
Bricks
Length Opening
(mm)
(mm)
No. of
Bricks
Length Opening
(mm)
(mm)
No. of
Bricks
Length Opening
(mm)
(mm)
No. of
Bricks
Length
(mm)
1
230
250
131⁄2
3230
3250
26
6230
6250
381⁄2
9230
11⁄2
350
370
14
3350
3370
261⁄2
6350
6370
39
9350
2
470
490
1
14 ⁄2
3470
3490
27
6470
6490
1
39 ⁄2
9470
1
2 ⁄2
590
610
15
3590
3610
1
27 ⁄2
6590
6610
40
9590
3
710
730
151⁄2
3710
3730
28
6710
6730
401⁄2
9710
31⁄2
830
850
16
3830
3850
281⁄2
6830
6850
41
9830
4
950
970
1
16 ⁄2
3950
3970
29
6950
6970
41 ⁄2
9950
1
4 ⁄2
1070
1090
17
4070
4090
1
29 ⁄2
7070
7090
42
10070
5
1190
1210
171⁄2
4190
4210
30
7190
7210
421⁄2
10190
51⁄2
1310
1330
18
4310
4330
301⁄2
7310
7330
43
10310
6
1430
1450
1
18 ⁄2
4430
4450
31
7430
7450
1
43 ⁄2
10430
1
6 ⁄2
1550
1570
19
4550
4570
1
31 ⁄2
7550
7570
44
10550
7
1670
1690
191⁄2
4670
4690
32
7670
7690
441⁄2
10670
71⁄2
1790
1810
20
4790
4810
321⁄2
7790
7810
45
10790
8
1910
1930
1
20 ⁄2
4910
4930
33
7910
7930
1
45 ⁄2
10910
1
8 ⁄2
2030
2050
21
5030
5050
1
33 ⁄2
8030
8050
46
11030
9
2150
2170
211⁄2
5150
5170
34
8150
8170
461⁄2
11150
1
9 ⁄2
2270
2290
22
5270
5290
1
34 ⁄2
8270
8290
47
11270
10
2390
2410
1
22 ⁄2
5390
5410
35
8390
8410
1
47 ⁄2
11390
1
10 ⁄2
2510
2530
23
5510
5530
1
35 ⁄2
8510
8530
48
11510
11
2630
2650
231⁄2
5630
5650
36
8630
8650
481⁄2
11630
1
11 ⁄2
2750
2770
24
5750
5770
1
36 ⁄2
8750
8770
49
11750
12
2870
2890
1
24 ⁄2
5870
5890
37
8870
8890
1
49 ⁄2
11870
1
12 ⁄2
2990
3010
25
5990
6010
1
37 ⁄2
8990
9010
50
11990
13
3110
3130
251⁄2
6110
6130
38
9110
9130
100
23990
1
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Bricks & Pavers Technical Manual
1.312
Section 1.3. Brick Masonry Construction
Brick Gauge
290 mm Long Bricks
No. of
Bricks
Length Opening
(mm)
(mm)
No. of
Bricks
Length Opening
(mm)
(mm)
No. of
Bricks
Length
(mm)
No. of
Bricks
Length
(mm)
1
290
310
132⁄3
4090
4110
261⁄3
7890
39
11690
11⁄3
390
410
14
4190
4210
262⁄3
7990
391⁄3
11790
2
1 ⁄3
490
510
14 ⁄3
4290
4310
27
8090
39 ⁄3
11890
2
1
2
2
590
610
14 ⁄3
4390
4410
27 ⁄3
8190
40
11990
21⁄3
690
710
15
4490
4510
272⁄3
8290
401⁄3
12090
22⁄3
790
810
151⁄3
4590
4610
28
8390
402⁄3
12190
3
890
910
2
15 ⁄3
4690
4710
28 ⁄3
8490
41
12290
1
3 ⁄3
990
1010
16
4790
4810
2
28 ⁄3
8590
41 ⁄3
12390
32⁄3
1090
1110
161⁄3
4890
4910
29
8690
412⁄3
12490
4
1190
1210
162⁄3
4990
5010
291⁄3
8790
42
12590
1
4 ⁄3
1290
1310
17
5090
5110
2
29 ⁄3
8890
42 ⁄3
12690
2
4 ⁄3
1390
1410
17 ⁄3
5190
5210
30
8990
2
42 ⁄3
12790
5
1490
1510
172⁄3
5290
5310
301⁄3
9090
43
12890
51⁄3
1590
1610
18
5390
5410
302⁄3
9190
431⁄3
12990
2
5 ⁄3
1690
1710
18 ⁄3
5490
5510
31
9290
43 ⁄3
13090
2
1
1
1
1
1
1
2
6
1790
1810
18 ⁄3
5590
5610
31 ⁄3
9390
44
13190
61⁄3
1890
1910
19
5690
5710
312⁄3
9490
441⁄3
13290
62⁄3
1990
2010
191⁄3
5790
5810
32
9590
442⁄3
13390
7
2090
2110
2
19 ⁄3
5890
5910
32 ⁄3
9690
45
13490
1
7 ⁄3
2190
2210
20
5990
6010
2
32 ⁄3
9790
45 ⁄3
13590
72⁄3
2290
2310
201⁄3
6090
6110
33
9890
452⁄3
13690
8
2390
2410
202⁄3
6190
6210
331⁄3
9990
46
13790
1
8 ⁄3
2490
2510
21
6290
6310
2
33 ⁄3
10090
46 ⁄3
13890
2
8 ⁄3
2590
2610
21 ⁄3
6390
6410
34
10190
2
46 ⁄3
13990
9
2690
2710
212⁄3
6490
6510
341⁄3
10290
47
14090
91⁄3
2790
2810
22
6590
6610
342⁄3
10390
471⁄3
14190
2
9 ⁄3
2890
2910
22 ⁄3
6690
6710
35
10490
47 ⁄3
14290
2
1
1
1
1
1
1
2
10
2990
3010
22 ⁄3
6790
6810
35 ⁄3
10590
48
14390
101⁄3
3090
3110
23
6890
6910
352⁄3
10690
481⁄3
14490
102⁄3
3190
3210
231⁄3
6990
7010
36
10790
482⁄3
14590
11
3290
3310
2
23 ⁄3
7090
7110
36 ⁄3
10890
49
14690
11 ⁄3
3390
3410
24
7190
7210
2
36 ⁄3
10990
49 ⁄3
14790
112⁄3
3490
3510
241⁄3
7290
7310
37
11090
492⁄3
14890
12
3590
3610
242⁄3
7390
7410
371⁄3
11190
50
14990
12 ⁄3
3690
3710
25
7490
7510
37 ⁄3
11290
100
29990
2
12 ⁄3
3790
3810
25 ⁄3
7590
7610
38
11390
13
3890
3910
252⁄3
7690
7710
381⁄3
11490
131⁄3
3990
4010
26
7790
7810
382⁄3
11590
1
1
1
1
1
2
1
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Bricks & Pavers Technical Manual
Section 1.3. Brick Masonry Construction
1.313
Blending
Raw materials for brick making are from natural sources and these vary in colour within any one deposit. Brick
makers blend materials to moderate the colour variation but it still occurs. Colour variation may be caused by
different conditions across the kiln. No matter how well made, bricks delivered to site will have some degree of
colour variation.
Poorly blended bricks may show unwanted patches, streaks and bands of colour in the finished masonry.
To avoid this:
•
All bricks required for the project, or as many packs as will fit, should be delivered at one time and stored
on site; and,
•
Bricks should be drawn from at least four packs simultaneously, working down from the corners of each
pack. ■
Brick Storage
Bricks stored on site should be covered and kept off the ground. Bricks may absorb ground water containing salts
or coloured minerals creating subsequent problems with staining. Bricks when laid saturated usually produce
excessive efflorescence as the masonry dries. Saturated bricks may also adversely affect the mortar bond
strength.
Moving bricks around the site may cause chipping and excessive movement of packs should be avoided. ■
ADV03795
Bricks & Pavers Technical Manual
Section 1.3. Brick Masonry Construction
1.314
Laying Practices
The following practices are recommended:
•
Mortar, extruded from tapping the brick down to the string line, should be cut off with an upward stroke of
the trowel. In this manner, a clean cut is made, without smearing the face of the brick.
•
Joints should be tooled progressively as the bricks are laid, when the mortar is firm to thumb pressure. High
suction bricks require joints to be tooled more frequently than low suction bricks. Tooling too late produces
a ‘burned’ joint, where the surface may not be smooth and dense.
•
After allowing the mortar to undergo initial set, within a day, dry brush mortar smears, to remove any dags,
and then wet brush any remaining mortar stains. Mortar that is allowed to set on the masonry face may
require high-pressure water jet cleaning or more costly, risky methods of cleaning.
•
Cavities should be kept as clear as possible from mortar droppings. Flushing out the cavity removes
inadvertently dropped mortar and ensures ties are clean and flashing and damp proof courses are not
bridged. It is poor practice and usually ineffective to flush large quantities of dropped mortar from cavities.
Usual practice is for the bricklayer to leave out one or more bricks at the base of the wall above a flashing
or the damp proof course for the washings to come out. Washings can cause serious staining where they
run down over lower brickwork and should be rinsed off thoroughly each day.
•
Scaffolding should be kept at least 150 mm from the face of the brickwork to prevent a build up of mortar
droppings against the masonry.
•
When bricklaying is interrupted by rain or rain is expected overnight, masonry should be protected by
covering it. Saturated masonry will produce excessive efflorescence and may lead to staining with some
bricks.
•
Face bricks are supplied with one face and one header suitable for exposing (i.e. to be seen after laying).
Face bricks with unwanted marks, chips or cracks on a header should be laid with that header inside a
mortared joint. Face bricks with unwanted marks, chips or cracks on the face should be set aside by the
bricklayer (or labourer) for use as commons. Boral will not be responsible for replacing bricks with unwanted
marks, chips or cracks that have been laid. ■
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Control Joints
Control joints must not be bridged by mortar or render. After laying the bricks or rendering, the joint must be
cleaned. Lumps of mortar or render can transfer forces across the closing joint and will cause the bricks to crack
(or spall). Control joints are usually constructed with a highly compressible material (in the form of a sheet or
rod) inserted to keep dirt and moisture from penetrating to the cavity. For aesthetic reasons a compressible
caulking material, matched to the mortar colour, is usually applied on the outside. As the joint closes,
compressible caulking compounds may be extruded from the joint but incompressible ones may damage the
bricks. If extruded caulking compound is considered unsightly, it can be cut out and replaced or the compound
can be recessed during construction. Care must be taken when choosing a caulking compound to ensure it is a
highly compressible type that will survive for the design life of the building and not discolour significantly. There
are numerous suitable materials available and manufacturer’s recommendations should be sought.
Where a control joint has flexible masonry ties built in, a piece of the compressible material must be removed to
accommodate the tie. ■
Damp Courses and Flashing
Membrane type damp proof courses (DPC) must be laid across the full width of the wall or leaf and must project
through the mortar on either side and be completely visible after laying and cleaning is complete. Recessing DPC
below the edge of the brickwork so that the mortar bridges the DPC invalidates its use and is therefore entirely
unacceptable. Bridged DPC may lead to rising damp, salt attack and or accelerated corrosion of the built-in
components that may lead to structural failure. Recessing flashing below the mortar although common is not
good practice as it allows the water that should be shed to soak into the wall below the flashing.
DPC and flashing at the base of a wall may be combined. Lengths should be as long as possible but where not
continuous, two adjacent pieces should overlap by at least 150 mm and if possible be sealed together. If a
termite shield is used in the same joint as the DPC, the DPC material must be compatible with the termite shield
or corrosion may destroy the DPC.
General practice has been to recommend that flashings and DPCs be sandwiched between the mortar. There is
some evidence that the common practice of laying flashings and DPC directly on the lower course of bricks and
placing the mortar on top may be superior in some instances. ■
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Cleaning of Clay Masonry
The Basics of Brick Cleaning
The cleaner the bricklayer leaves the wall, the easier will be the cleaning task. The majority of the mortar
residues and smears should be cleaned before they set hard. However, in most cases some additional cleaning
will be required to completely remove the mortar residue.
Cleaning techniques may involve high-pressure water jet equipment or hand methods. Whatever technique is
used, the following requirements must be observed to ensure additional staining problems are avoided.
Test Areas
Testing in one or more small areas is the safest way to determine the correct technique and chemical solution to
remove mortar residues. This must occur well before final cleaning, as it will usually not be possible to assess
the effectiveness of the test clean until the masonry dries.
Clean Soluble Salt Deposits First
Efflorescence, a white ‘fluffy’ deposit, cannot be removed by water or acid. Dry brushing to remove the
efflorescence before washing is recommended. If efflorescence is wetted, the salts go into solution and are
drawn back into the brickwork and will reappear as the masonry dries. Efflorescence will eventually disappear
through natural weathering.
Vanadium salts produce a green or yellow efflorescence or stain (mainly seen on cream and light coloured clay
bricks). Hydrochloric acid will make these stains much worse and may make them impossible to clean. Mild
vanadium stains may be treated with sodium hypochlorite (household bleach). Spray or brush on dry brickwork
and leave until the stain disappears, then rinse off. Proprietary mould cleaners containing sodium hypochlorite
and sodium hydroxide can be used as above and have been found very effective. Proprietary brick cleaners may
also be effective and should be used only according to the manufacturer’s instructions. Proprietary cleaners
usually contain acids that must be neutralised after use with a solution of 15 grams of washing soda
per litre of water.
More than one chemical application may be required and the walls should be rinsed thoroughly after each
treatment. t
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Cleaning of Clay Masonry (continued)
High Pressure Cleaning
High-pressure water washing is now common for cleaning brickwork. If used the pressure must be kept below
1000 psi (7000 kPa), the nozzle must be kept 500 mm from the brick face and the nozzle must be a wide fan jet
type with an angle of 15 degrees.
The following practices must be observed:
•
Cleaning should not start until the mortar has hardened.
•
Hard lumps or persistent smears should be removed by hand.
•
Mask adjacent materials.
•
Do not apply the acid with the high-pressure sprayer. Use a low-pressure spray or broom it on.
•
Clean from top to bottom in small sections.
•
Work in the shade, ahead of the sun, if possible.
•
DO NOT USE EXCESSIVE PRESSURE OR GET TOO CLOSE, as this will damage the face of the brick and the
mortar joint. Mortar joints that are no longer smooth with sharp edges is a clear sign of excessive pressure.
Excessive pressure is used to make cleaning faster; it does not do a better job of cleaning. t
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Cleaning of Clay Masonry (continued)
Saturate the Wall Surface
Failure to completely saturate the surface of the wall is in itself a major cause of cleaning stains. Cleaning
solutions containing dissolved mortar particles and acids will be drawn into a dry masonry wall, causing staining.
Furthermore, saturating the surface of the wall keeps the acid solution on the face of the masonry where the
mortar smears are present. It is not true that face saturation weakens the acid and slows the cleaning.
Water should be trained on the wall until the brick suction is exhausted. The area to be cleaned must be
saturated as well as all brickwork areas below. If the wall appears to be drying on the surface, reapply water
until ready to apply the cleaning solution.
Recommended acid strengths are based on application to a surface saturated wall.
Note: This point must be strictly adhered to for bricks manufactured in Queensland. Their raw materials contain
large amounts of iron oxide and failure to saturate the surface of the wall allows acid solutions to react
with the iron oxide and create severe iron oxide staining. Failure to saturate the surface of the bricks
manufactured in other parts of Australia can also lead to the acid reacting with iron oxide but to a much
lesser degree. This form of staining is known as acid burn and is particularly visible on light coloured
bricks. Acid absorption into bricks can also lead to vanadium and manganese staining. t
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Cleaning of Clay Masonry (continued)
Acids – The Basics
The traditional masonry-cleaning chemical is hydrochloric acid, (also known as muriatic acid or spirits of salts).
Its main function is to dissolve the cement in the mortar mix. It has few other uses and in many stain situations
should not be used.
Hydrochloric acid is a corrosive S6 poison and care must be taken when using it. If acid is splashed onto the skin
it should be immediately swabbed with clean water, or more effectively, with a solution of bicarbonate of soda
in water, which will neutralise the acid.
The recommended acid strength for light coloured clay bricks is 1 part acid to 20 parts water and for other bricks
is 1 part acid to 10 parts water. Acid takes time to dissolve the cement and should be left on for 4-6 minutes (or
longer if needed) before washing off. After washing a solution of 15 g per litre of washing soda or 24 g per litre
of sodium bicarbonate should be sprayed on to neutralise any remaining acid. Excess hydrochloric acid will
eventually evaporate from the brickwork, however, it is likely to cause staining of the bricks and damage to
built-in components. Other acids such as sulfuric acid or nitric acid will not evaporate and are not used in
brick cleaning.
Note: The recommended strength must be strictly adhered to. Bricks manufactured in Queensland may contain
large amounts of iron oxide and the use of acid solutions stronger than 1 part acid to 20 parts water can
dissolve these particles and create iron oxide staining. For light coloured bricks manufactured elsewhere
the use of solutions stronger than 1 part acid to 20 parts water can lead to acid burn.
Proprietary masonry cleaning solutions containing a mixture of acids are available. If used, the manufacturer’s
recommendations must be strictly adhered to. Excessive and incorrect use of some proprietary cleaning solutions
has in the past, produced very bad staining. t
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Cleaning of Clay Masonry (continued)
Safety Precautions
All masonry-cleaning acids are dangerous. Acids that do not dissolve cement as quickly as hydrochloric acid are
not necessarily safer and can be very much more dangerous to human health. To avoid personal injury:
•
Wear goggles, gloves and protective clothing.
•
Always pour acids into water – this avoids splashes of highly concentrated acid onto the operator.
•
If splashed onto the body, wash with clean water and if possible, neutralise with a mixture of bicarbonate
of soda and water.
•
The manufacturer’s instructions and safety precautions must be strictly adhered to if proprietary cleaning
products are used. ■
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