Frequently Asked Questions | Page 2 | Clay Brick Association of Southern Africa

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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 brick do I use to build a fire wall?

Question continues: "The walls are 3m high by 4.5m wide by 0.2m thick, and supported at each end of the 4.5m I believe this will have a fire rating of 240 minutes? How do I support the wall for strength against wind? Are steel wire wall ties sufficient? "

ANSWER

You do not need a special type of brick such as a fire brick. I suggest a double skin masonry wall in standard imperial clay brick, with each leaf 106 mm in thickness. This will yield an overall wall thickness (unplastered) of 212 mm which will have a nominal fire rating of 240 minutes.

I would recommend supporting each 4 meter length of wall with a 340 x340mm brick pillar at each end, as well as using wire ties (brickforce) as suggested.

Chris Dickinson
Corobrik

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...

Should I seal my paving?

Mark Hunter-Smith of Algoa Brick advises:

"Any form of sealant or dressing on a brick automatically turns a maintenance free product into one that has to be maintained as the sealer will weather and or peel off over time. The only time this has limited success is internal feature walls that are protected from the elements. Sealing traps moisture in the bricks and wall and cause softening and failure of the mortar. In most older buildings you will be able to see that the bricks to not fail, it is the mortar that crumbles or splits.

"Applying a sealer to an external paving situation is probably the hardest to do as it is totally exposed to weather as well as car tyre abrasion etc. It has no roof overhang to protect or vertical walls for rain to run down i.e horizontal surface taking full pounding. I do not think a sealer will last very long in this application especially in the high wear areas which can create a patchy type finish. Also a sealer makes the paver waterproof so rain water pooling occurs and also surface can become rather slippery.

"I would suggest rather a good clean with a high pressure setting of a garden hose using industrial type soap like...

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...

What is the white, powdery substance on my bricks?

Efflorescence is a powdery deposit of salts which forms on the surface of bricks and paving. It is usually white but efflorescence can be yellow, green or brown.

Efflorescence does not in any way influence the structural strength of clay bricks or pavers. Roman buildings that have been standing for 2 000 years can show efflorescence

A temporary efflorescence is particularly common on new brickwork and paving as soluble salts are dissolved and transported to the surface of the brickwork and paving by water. The efflorescence on new well fired brickwork and paving may be unsightly, but it will not cause damage unless the brickwork and paving are under-fired or soft-fired, in which case serious efflorescence can cause flaking of the surface of the brick or paver.

Efflorescence can occur from a variety of sources. Besides the brickwork, soluble salts can originate from the sand, mortar and the water used. Ground waters that are naturally salt-bearing can be drawn into the base of the brickwork and paving.

Remedies

The best removal method is simply to brush off the deposit with a stiff dry bristle brush after the wall has dried out. Collect the...