Building with bricks | Clay Brick Association of Southern Africa

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How much water can a clay brick safely absorb?

The acceptable water absorption rate for face bricks ranges from 4.5% to a maximum of 12%.

The acceptable water absorption for clay plaster bricks is between 12% and 20%. If you are using engineering bricks the closer you are to the 12% the better the result will be. When the water absorption rate of a plaster bricks is too low, i.e. below 12%, it may be difficult for plaster to obtain a proper adhesion to the plaster brick.

Handmade historic bricks; many of which are often found to have an average porosity value of around 35%.

With highly porous bricks there is a danger that they might rapidly absorb moisture from the bedding mortar (particularly in warm weather) causing it to stiffen quickly. This would result in it losing the all-important characteristic of plasticity that would inhibit correct and accurate positioning to line and face-plane and the provision of a secure bedding, leading to poor adhesion with attendant negative consequences on aspects of compressive and flexural strengths of the overall walling.

It is important not to confuse ‘porosity’ with ‘permeability’, as they are not the same. Porosity is a measure of...

How is brickforce used in unreinforced walling?

Firstly, what is Brickforce?

Brickforce is a British brand consisting of two main parallel wires joined by in-line welded cross wires. Main wires are manufactured to a flattened profile to simplify location into the mortar joint without steel build-up problems at lap positions corners/junctions or when used in conjunction with wall ties.

There are various other materials that can be used for brick reinforcement, e.g. Mild steel reinforcing rods and expanded metal. These products and others suitable as brick reinforcement are obtainable in rolls of varying lengths and widths, from your local hardware shop or builder supplies merchants.

Why use masonry reinforcement?

Masonry has excellent compessive qualities and the majority of buildings constructed using this material last for many years with little maintenance. However, masonry has no significant tensile strength and movement caused by substrata changes, moisture or thermal effects can cause cracking.

The use of masonry reinforcement is a very simple and cost-effective way of greatly enhancing the strength and durability of masonry construction by providing both structural and crack...

What are the basics of laying bricks?

Are you planning a major project? Our user friendly guide "Bricklaying made Easy" is available at Builders Warehouse, or from the CBA for just R150.

Preparation

Plan site layout e.g. position of building, material stores, access etc.
Store and protect all materials to minimise saturation and contamination.
Control the wetting of bricks in hot, windy weather.
Do not lay surface saturated bricks.
Set out at ground level to locate all openings before commencing bricklaying.
Lay out dry and minimise broken bonds.
Prepare and take care of gauge rods - they are important quality control equipment.
Work all levels from one datum.

Protection of brickwork

The best treatment is to prevent it from getting dirty in the first place - so protect the wall as work progresses from mortar droppings. After the first course of bricks has been laid - protect the base of the wall by laying sand, straw, sawdust or plastic sheeting along the ground. This minimises mud splashes and damage from mortar droppings.

As clay brickwork should be kept dry as possible during construction, cover the...

Should new clay bricks be left to dry out before use?

Clay bricks expand fractionally after leaving the kiln (primarily due to moisture in the air) and minute increases in height and width (0.006 percent per annum) continue at a decreasing rate for up to 5 years.Fortunately with clay products the majority of this expansion happens almost immediately the product leaves the kiln and is exposed to atmosphere.

Building walls without control joints that exhibit cracking, appeared to have expanded only 2mm to 4mm;

In the good old days all the bricks would be purchased at the beginning of a project and stored for many months before being used. It was thought this gave them an opportunity to harden and "dry out". Today, purchases are JIT (just-in-time) and the timing from order email to delivery to use is less than a week. The age of bricks in stock will vary considerably from factory to factory and region. Obviously if product is in high demand they do not stand too long in the yard before delivery.

There are many sources of movement in walling and paving including ambient moisture levels, temperature, loading and creep, chemical action, ground movement and settlement. For more information, please download the "...

Mortar: what materials do I need?

The cost and quality of masonry work is significantly affected by the mortar used. Mortars may account for as little as 7% of the volume of the walls, but the role it plays and the influence it has on performance are far greater than the proportion indicates. Mortar provides a bed for laying; bond units together to give compressive and flexural strength and seals joints against rain penetration.

Four types of building mortar are detailed in SABS 0164.

COMMON CEMENT	Sand
COMMON CEMENT	Lime: sand
COMMON CEMENT	Sand plus mortar plasticizer
MASONRY CEMENT	Sand (common = Portland)

Approximate proportions for mortar:

MORTAR CLASS

COMMON CEMENT lt...

Mortar: what are my mixing quantities?

Mortar must not be used after it has started to set, which usually occurs about two hours after it has been mixed. One man – particularly if he is a weekend builder – can probably lay a little more than 60 bricks an hour. If you are working on your own or with one assistant, it is better to mix a number of small batches as they are required than to mix a one-bag batch. Do not use too thick a layer of mortar between bricks or blocks; this is wasteful and may lead to cracking.

Mortar class

Class I: Highly stressed masonry incorporating high-strength structural units such as might be used in multi-storey load-bearing buildings; reinforced masonry.
Class II: Normal loadbearing applications, as well as parapets, balustrades, retaining structures, and freestanding and garden walls, and other walls exposed to possible severe dampness. In practice, Class II mortars are used for most applications.

The amount of water added to a mix must be enough to make the mix workable and plastic

Masonry cement must comply with SANS 50413-1: Strength class 22,5X. The addition of lime to masonry cements is not permitted

MORTAR:

... ...read more

What bonds or jointing should I use?

Bonding brickwork means the arrangement in brickwork so that the units are tied together to form a solid mass. The load is then evenly distributed along the length of the wall.
These drawings show what happens to a wall that is not bonded and one that is bonded.

There are two methods of lapping:

The half brick lap
The quarter-brick lap, also known as the half bond and the quarter bond.

If bricks are so placed that no lap occurs, the cross joints or perpends are directly over each other, and we have what is known as ‘straight joints’, which must be avoided at all costs.

There are basically three types of bonds used in South African construction and examples of all three can be seen in all towns and cities, - the Stretcher Bond, English Bond and Flemish bond.

Stretcher bond
(alternate layers of stretchers)

Consists of bricks laid lengthways along the line and mapped. This is by far the most commonly used bond in South Africa. In cavity wall construction this is the most economical bond to employ.

English bond
Consists of alternate courses of headers and...

Should you wet clay bricks before using them?

Well-made clay bricks should never require wetting before laying except (rarely) under extremely hot and windy conditions.

Pressed or extruded bricks of low porosity should never be wetted prior to bricklaying as they naturally have a significantly reduced water uptake (and almost zero with a Class A engineering brick) that, if wetted, would result in the brick retaining a thin film of water on all its surfaces and this would cause it to ‘swim’ on the bedding mortar; and that invariably leads to it both sliding out of face line and sinking out of level. If this happens adjust the water content of the mortar so that it is used as stiff as possible.

Clay bricks purchased from non-accredited sources could have unacceptably high porosity and water absorption rates and might need to be soaked on site with water before being used.

What is the difference between cement, concrete and mortar?

Cement

Cement is a binder. Similar to flour in a recipe, the purpose of cement is to hold the other materials together. But you can’t just use cement alone. You need the other materials and what you mix with the cement will determine the final product.Cement is made from limestone, calcium, silicon, iron, and aluminum, among other ingredients. This mixture is heated in large kilns to about 2,700°F (1,482°C) to form a product known as clinkers, which roughly resemble marbles. These are ground into a powder and gypsum is added, creating the gray flour-like substance known as cement. When water is added to cement, it triggers a chemical process that allows it to harden.There are many different types of cement, but the type most commonly used in construction is Portland cement.

Concrete

Concrete is a composite of aggregate (such as sand or gravel), cement, and water. The cement makes up from 10 -15% of the total mass of concrete; the exact proportions vary depending on the type of concrete being made. Aggregate makes up more than 60% of a concrete mix — and up to 80% in some cases. The aggregate gives the concrete its mass...

What is the recommended gap for clay pavers?

The gaps on the pavers are 2mm to 6mm, which are to account for both PA and PB pavers so that lines may be maintained. (see the tolerances in the spec’s on both types of pavers)

The "nibs" technically are only to assist with laying and are not for any structural reason. Most nibs are offset so as not to end up contacting each other, but strictly speaking, the jointing material is designed to diffuse the lateral and vertical forces by transferring them through to the bedding sand and sub-bases layers.

It is highly recommended that the grade of jointing material is different to the bedding sand, to expand in the joints and create the lockup. It must also be vibrated so that it fills the joint to the bottom and in so doing allow the forces to be transferred through. Again, one of the more important issues in the design is the edge restraint which holds the whole system together, and patterns relevant to the usage are also critical.

Please download the "Movement of Brickwork" technical paper.

What are the duties of a Construction Health & Safety Officer?

The SACPCMP prescribes the registration of Construction Health and Safety Officers as a specified category in terms of section 18(1) (c) of the Act No. 48 of 2000. See the attached document for full guidelines. For additional detail about registration and services, see the website of The South African Council for the Project and Construction Management Professions (SACPCMP) (www.sacpcmp.org.za).

Services of the Health & Safety Officer during the construction phase of a project include:

Assist with the preparation of a construction health and safety plan
Confirm necessary documentation was submitted to the relevant authorities
Attend project planning meetings
Assessments and approval of contractor(s) health and safety plans
Attend the contractors site handover
Attend regular site, technical and progress meetings
Facilitate site health and safety meetings
Identification of the hazards and risks relevant to the construction project through regular coordinated site inspections
Establish and maintain health and safety communication structures and...

Can I use a cleaning machine on paving?

The following recommendations deal with vehicles and associated equipment and their use:

High Pressure washers should not be used on clay brick, as they remove the surface which will result in deterioration over time.
Equipment should be purpose designed to sweep the particular area. If there is any doubt, the vehicle manufacturer should be consulted.
Tyres should be inflated according to the manufacturer’s recommendations to ensure maximum weight distribution.
Polypropylene, not wire, brushes should be used.
Sweeping brush pressures should be set to the minimum required to suit the particular task, i.e. surfaces swept regularly will require a lesser setting than those swept infrequently or those covered with heavy deposits.
When sweeping, engine revolutions should be set at the minimum required to maintain vacuum (suction) pressure.
Operators, including reliefs, should be trained to vehicle manufacturer’s recommendations and tyre and brush pressures should be regularly checked.
Advice should be given to operators that, when equipment is stationary or left unattended, suction, brush rotation and water...