What’s that white powdery stuff that can appear on brickwork?
Well the technical name is Efflorecence
It can also appear on concrete!
What Is Efflorescence, & How Is It Caused?
Basically it is caused by water soluble salts contained in either the mortar, or the bricks.
When any water in the wall (that has dissolved the salts) comes to the surface of these building materials the water evaporates, leaving the salts on the surface.
Although the salts sometimes come from the bricks, more commonly they originate from the mortar.
Although some efflorescence may be as a result of the initial construction water; walls that are regularly wetted can have more persistent issues, for instance:
Uncapped garden walls.
Retaining walls.
Walls exposed to driving rain.
Efflorescence is more prevalent on South and East facing walls as these are colder so the moisture gets to the face of the wall. North and West facing walls are generally warmer so the water evaporates before it reaches the surface leaving the salts inside the walls.
What Can Be Done To Prevent Efflorescence?
There are several things that can be done to minimise efflorescence including:
Overall design to keep water out of the wall structure.
Specifying Mortar Joints to keep water off the wall.
Protecting bricks from weather before they are laid
Specifying low alkali cement.
Specifying Washed Sand
Using a mortar admixture to minimise the water cement ratio.
Dealing With An Existing Problem
Probably the first step when dealing with an existing problem is ensuring the wall can be kept dry.
As long as there is a path for water to get to the surface it will be very hard to deal to achieve a permanent solution as water will continue to evaporate on the surface bring out fresh salts.
When removing the actual efflorescence its best to try a stiff brush first.
If this doesn’t work you can try hand washing again using a stiff brush. (Although it is tempting to wash the soluble salts off with a pressure washer the water can penetrate into the wall and then as the brickwork dries bring further salts to the service)
The final suggestion is to use a special chemical efflorescence removal chemical. (These tend to be acid based and need to be used exactly as the manufacturers recommend)
Brick ties, although small, have an important part to play in the structural strength of your new home.
In brick veneer construction, ties are used to pass all the sideways forces across the cavity (such as from wind) to the frame.
For double brick construction the ties share the forces between the leaves.
They prevent lateral movement at expansion and articulation joints.
Special ties also connect walls where bonding of masonry is not practical.
Effectiveness
Probably the biggest test of brick walls in Australia was the 1989 Newcastle (NSW) earthquake. . . . Generally brick walls survived well except where there were problems with the ties such as:
Rusted through galvanised ties;
Ties not properly connected;
Missing ties;
Incorrect ties used.
Types
Ties are available in a wide range of types and in various strengths such as heavy, medium and light duty. (Ancon Building Products have a very informative downloadable guide)
The tie illustrated above is a galvanised stamped steel plate tie, used to connect the brickwork to a frame. The tie is nailed to the frame (through the hole at the top) and the corrugated end is incorporated into the mortar joint of the brickwork. The section of tie which spans the cavity is shaped to shed water.
In the case of a double frame construction a wire tie with loops at each end, or a figure of 8 shape,are the common choices of ties.
Common Materials are:
Galvanised Steel – Most common type.
Stainless Steel – For high exposure locations or very long life. (Seem expensive but only a small component Thof overall building cost)
Plastic – Mainly for acoustic applications.
Spacing
Check with your Structural Engineer but for a typical medium duty application:
Vertical Spacing 600mm but 300mm around openings
Horizontal Spacing 600mm for Double Brick OR every main stud for Brick Veneer (normally 450mm for external walls and 600mm for internal walls
More information can be found in the Australian Standard AS3700 .
If you want a rendered surface on your retaining wall one of the best ways of achieving this is by using ‘Besser Blocks’.
These are hollow concrete blocks which are designed to incorporate steel reinforcement within the block.
A few issues when building these walls are:
Don’t skimp on the foundation. Even a 600mm high wall will need a concrete foundation 600mm wide by 250mm deep.
Make sure that the cement grout is well packed around the steel reinforcement.
Buy some of the yellow safety caps you see here to put over the reinforcement bars and ‘Keep Yourself Safe.
Don’t backfill behind the wall for at least a week
As well as free standing retaining walls Besser Blocks are also used as basement walls and to provide structural strength for external walls when building against a slope.
This photograph shows a typical example where the Besser Block wall will provide the external wall of a garage. ( You can also see the builders plastic which will form part of the ‘tanking’ to keep damp from passing through the wall)
When you are looking round your new home build you may think “What’s that gap between the window and the brickwork?” . . . . . . .or even “Why is there a vertical gap between the bricks in the middle of the wall?”
Before you panic it might be worth checking if it is an Articulation Joint.
Why Are There Articulation Joints?
Brick Veneer houses can move for several different reasons including:
Temperature
Humidity
Movement of the frame
‘Flexing’ of the foundation
As the structure moves articulation joints are used to accommodate these movements in the structure without cracking.
Unless the soil has been classed as either A or S (see: Soil Classification) vertical articulation joints must be installed in any un-reinforced masonry walls.
Location
In straight walls without openings, the articulation joints must be at a maximum spacing of 6m. They must not be closer than the wall height from the corners.
Where there is a door or window its normal practice to put the joint alongside so they are less obvious.
Construction
For articulation joints next to windows and doors a gap of 10 mm must be left between the edge of the frame and the brickwork.
In a plain wall the gap between bricks again should be 10mm.
The space between the bricks is taken up with a foam filler with a flexible seal on the outside face keeping water out.
The bottom of this photo shows what the finished seal should look like . . . . . . . the top part shows a problem that will needs to be sorted. (normally this tearing of the sealant from the brick is caused when the sealant is too thin)
What you can’t see is that during the construction the bricklayers should be inserting expansion ties across the joint.
During construction it is well worth checking that there is NO MORTAR in the joint. . . . Any mortar will stop the joint acting as it should and can cause cracking over the next few years.
Unfortunately brickwork overhanging the slab like this is more common than it should be. . . . but it’s often not the brickie’s fault.
How it Happens
Normally the problem is that the slab has been constructed smaller than the required dimensions.
This wouldn’t be a problem, but for the fact that most houses come with prefabricated frames which mean the frame is too big for the slab. If the frame components aren’t ‘adjusted’ to make them smaller they will overhang the slab, and as a consequence the bricklayer overhangs the brick to maintain the wall cavity.
How Much Is Too Much?
The Building Code of Australia (BCA), Part 3.2.2.7, Edge Rebates, states ‘Exterior masonry must not overhang more that 15mm past the edge of the slab’.
Interestingly the maximum overhang permitted for the frame is only 10mm from the edge of the slab.
Solution
To my mind the best solution is to bolt a steel angle to the slab using masonry anchors.
The reason the masonry anchor is 50mm from the top surface of the concrete is to prevent it breaking out.
I have heard of people suggesting pouring concrete, or a cement grout I wouldn’t recommend that. To do it properly would require dowel bars to be drilled into the concrete and reinforcement fixed before trying to bond a thin piece of concrete to the slab.
For the typical modern house with slab on ground base there are two minimum heights above ground level that need to be considered:
Next to the building.
Distance of 1m away.
The reason for these minimums is to keep water out of the building, including the structure and foundations.
Next To The House
Floor level above external finished surfaces must be a minimum of:
50 mm above impermeable (covered paved or concreted areas) that slope away from the building
100 mm above the finished ground level in low rainfall intensity areas ( 5 minute intensity of less than 125mm/hour for a recurrence interval of 20 years -see: Rainfall Intensity to check your site), or sandy well-drained areas
150 mm in any other case.
Distance of 1m
The external finished surface surrounding the slab must be sloped away from the building, for the first 1m by a minimum of the following:
25 mm in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving)
50 mm in any other case.
Normally in clay soils I would allow another 15-20mm to allow for any ‘Soil Heave’. (See:Building on Clay Soils)
Overall
To meet the Building Code the range of total heights above ground will vary between 75mm and 200mm depending on circumstances. If you want a smaller step between inside and outside (for reasons such as Better Accessible Design) you will need to talk with your House Designer about a detail which meets the intent of the Building Code (Keeps water out of the house).
I hear a lot of people agonise over the choice of bricks for their new house.
That’s probably because they are:
Looking Too Closely. At the builders display centre you may be handed individual bricks or see a board with about 8 bricks on it. When you have been in the house a month you probably won’t notice the individual bricks. You only see the overall effect.
Taken In By The ‘Hype’. Brochures use words like Premium, Valued, Crafted and other ‘Bulldust’. (see ‘Brochure Bulldust’ below)
Brochure Bulldust
These premium bricks are derived from the uniquely textured and blended heritage of the original “hand made” English bricks. It is these timeless characteristics that have been applied by highly skilled craftsmen to a range of clay colours.
The palette now includes subtle grey blends, warm, earthy reds & tans, bold coffee browns and deep black tones.
This premium range of genuine clay bricks are unique and highly valued by building professionals. The range is a statement of luxury befitting premium homes, residential developments and commercial applications.
Translation
In the old days when all work was done by hand it wasn’t practical to mix clay to get a consistent colour, so you got what came from the raw clay.
These bricks are machine made with a mix of clay colours, but we think we can charge a lot more for them.
HINT
When choosing bricks go to a Brick Suppliers Display Centre and only look at bricks panels from at least 3m away. It much easier to see if a cheaper brick gives the effect you want.
I have previously carried out a worked example of the insulation of a Brick Veneer Wall, so as a comparison here is double brick wall.
I have also shown (in brackets) the effect of using a hebel block in place of one of the brick ‘leaves’:
Element
R value
Outside surface air layer
0.03
110mm brick
0.08
25mm cavity
0.12
110mm brick (*or 125mm Hebel Block)
0.08 (*0.81)
Plasterboard 10mm
0.08
Inside surface air layer
0.12
Total R value
0.51(*1.24)
U value = 1/R
1.96 (*0.81)
The heat losses or gains for 150 sq m (fairly typical external wall area) of this type of double brick wall at 15 degrees above, or below, outside temperature will be:
Area x ‘U’ x temperature difference = watts per hour
150m2 x 1.96 x 15degrees = 4410watts per hour
Heating/Cooling Requirement = 4.41kw/hour
Using Hebel for one of the leaves will improve the heat loss as follows:
150m2 x 0.81 x15degrees = 1822watts per hour
Heating/Cooling Requirement = 1.82kw/hour
Still not as good as the 1.17 kw/hour of the typical brick veneer construction
Don’t forget heat is also lost through windows, ceilings floors and ventilation.