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What are bricks made of?

The different clays extracted from a number of areas across the country often dictate the colour and properties of the finished brick, providing a clear indication of the clay’s origin.

Clay bricks and pavers are made up of a great variety of natural clay deposits which together with the firing characteristics of the manufacturing process govern the resulting properties of the brick or paver.

The clay is crushed and mixed with water to form a pliable material which can be moulded into different shapes and sizes. Once fired to a very high temperature it reaches a hard and weather resistant form.

What is the embodied carbon dioxide in clay bricks?

The current figure for total embodied energy CO₂for clay bricks 0.252 tCO2e/t, a slight increase on the 0.244 tCO2e/t reported for 2008.

Can bricks be reused?

Bricks and pavers can be reused as can buildings made of brick. Bricks are among the most commonly reclaimed building materials. Reclaimed bricks may also be used in buildings, road construction or can be crushed and used in landscaping.

Around the world there are many examples of old brick buildings and structures being reused as offices, apartments, theatres or entertainment venues.

What is the brick industry doing to reduce carbon emissions?

The main atmospheric emissions resulting from the production process are carbon gases, hydrogen fluoride and particulates. The brick industry has been working for many years to reduce the impact of such emissions. It has undertaken research and development into methods of process modification, participated in the production of process guidance notes on ways to reduce hydrogen fluoride and particulates emissions and made major capital investment in the latest technology such as filters and scrubbers. It is a clear objective of the brick industry to increase the percentage of production capacity covered by systems accredited to ISO 14001 or EMAS and to ensure that all legislative standards set for the control of emissions, toxic waste and environmental management are achieved.

We are building a new extension to a building. How do I find a match for the brick? It is possibly no longer made?

There are over 1200 types of brick on the market ranging from handmade stocks to extruded wire cut facing bricks in a multitude of colours and textures. The good news is that a close match should be found from newly manufactured bricks. If you decide to find a match, you can obtain a list of our current members here. Our members produce over 95% of the clay bricks and pavers sold in the United Kingdom and the Republic of Ireland. They will be able to provide you with catalogues and brochures to view the wide choice available. Once you have made a short list of possible matches you can obtain samples from the manufacturer who will be willing to give advice and help you further.

Some builder’s merchants specialise in brick and help with matching; a local one may help you find a suitable match and may offer to visit you to see the original.

We live in a house that has been extended at various times over the years. The bricks do not match in colour and our estate agent has told us that this reduces the value of the property. We have heard there is a way of changing the colour of the bricks permanently with some kind of dye or stain, is this true?

Yes, there is a technique for tinting brickwork, which has been used with success for well over thirty years. Experience has shown that tinting is a permanent modification of the colour and treatment of the brick but has no adverse effects on the durability or other performance attributes of the brick. The process consists of applying a colourfast oxide based pigment in a potassium silicate medium, which gives a permanent tint to the surface of brick masonry. It can be used to tint brick as well as mortar joints.

British Standards exist for the pigments used in the tinting, but there are none for tinting procedures. The techniques involve specialist knowledge and skill and are therefore best left to specialist contractors rather than a general builder.

We do not endorse the work of individual companies or craftsmen providing services in the construction industry. Note that there are few specialists offering this service.

We have the name of a brick; can you tell me who the manufacturer is?

We maintain an ever changing database of bricks and their manufacturers that may contain your particular brick. Contact us.

We want to build a new driveway with clay pavers, can you give us a few tips to get started?

First select the method of laying the pavers. There are two approaches, flexible and rigid.

Flexible is more advantageous in that it is easier, more economical, quicker and a dry process which can be driven on immediately, upon completion. Flexible paving can also be taken up, altered and reinstated. Essentially the flexible system consists of pavers close butted and laid on a 30-50mm uniform bedding course of sand on a compacted granular base. The fine joints are sand-filled. It is essential to ensure that a suitably robust edge restraint is provided to prevent the lateral spread of the pavers and the opening of the joints. Edge restraint may be provided by existing features such as walls or purpose made kerbs or channel details.

The rigid system looks different because it has more obvious joints filled with mortar. Some people think it has more aesthetic appeal because of its joints, but it is slower and harder to construct and requires more skill to lay and can be more expensive. Pavers are laid on a 20mm mortar bedding on a rigid concrete foundation and the joints between them, typically 10mm wide are filled with mortar.

I would like some information on designing a brickwork garden wall. Can you give me some advice about the design and detailing to be considered?

You can view our publication Design of Free Standing Walls which provides much detail in this area.

The most critical consideration when designing a freestanding wall is to make sure that it is adequate to resist severe gusts of wind. For walls no more than two metres in height there are simple guides that provide adequately stable construction. Another good guide is Building Research Establishment Good Building Guide 14 – Building Simple Plain Brick or Block Work Freestanding Walls.  For walls greater than two metres in height seek the advice of a structural engineer.

The following types of construction can be selected for stability. Piers may be incorporated, preferably projecting both sides of the wall. Alternatively, if space permits, staggering or curving the wall in plan is an option. For greater stability or taller walls, diaphragm forms, reinforced piers and chevron plan shapes can be considered.

Regardless of the structural requirements, detailing is extremely important in order to protect the brickwork from deterioration by the weather and to develop special features. A freestanding brick wall is far more exposed to weather conditions than an external wall in a building.

First the wall should incorporate a damp proof course (DPC) at its base consisting of two courses of DPC bricks. A flexible sheet DPC is not recommended as this can affect stability. At the top, a coping or capping brick will be required depending on the durability designation of the bricks selected. If ‘F1’ (Moderately frost resistant) bricks are chosen, a coping will be needed that projects a minimum of 50mm each side incorporating throated drips. In addition a flexible high-bond DPC such as a bitumen polymer giving good bond strength sandwiched between mortar will be needed below it.

If an ‘F2’ (Frost Resistant) brick is selected, a capping will be adequate but it is recommended that the same kind of high bonding DPC is included below it to protect the brickwork from possible staining. Both capping and coping materials must be frost resistant. Movement Joints should be spaced at maximum intervals of approximately twelve metres.

Mortar mixes should be compatible with brick types and suitable for the level of exposure. Generally the main body of the wall should be designation (III) or (II) and for the coping /capping course (II) or (I). Sulfate resisting cement may be necessary with bricks of ‘Normal’ soluble salts content.

As most freestanding walls will be at least one brick thick they will provide an opportunity to use one of the Garden Wall Bonds. If it is to be fair faced both sides, it may be necessary to select bricks for the through the wall headers for size consistency.

I am designing a new building. Can you give some information about the type of joint filler that is required for movement joints in long runs of brickwork walling?

Our publication Vertically Restrained Clay Brickwork Cladding provides a wealth of detail in this area.

Generally unrestrained and lightly restrained clay brickwork will tend to expand during the life of the building due to thermal and moisture movement changes. The spacing and thickness of movement joints in such walls is contained in Code of practice for use of masonry BS 5628: Part 3: 2001: Materials and components, design and workmanship. You can obtain the latest version from the BSI.

As a very general guide, spacing is commonly between 8 and 15m, depending on the brick type and the wall in question. The width of the joint in millimetres should be about 30% more than the distance between the joints in metres but it is advisable to seek advice from the filler manufacturer. Thus movement joints at 12m centres will need to be about 16mm wide.

The compressibility of the joint filler is possibly the most critical factor in the design of an adequate joint for fired-clay brickwork. A foam material that can be squeezed between finger and thumb to 50% of its original thickness has the approximate compressibility. Flexible cellular polyethylene, cellular polyurethane or foam rubbers are the most satisfactory materials. Hemp, fibreboard, cork and similar materials should not be used for movement joints in fired-clay brickwork.

The width and depth of seal for movement joints is important. To ensure adequate bond to the masonry the depth of the seal should be at least 10mm. Certain single-part moisture cured sealants are best used in joints of small cross section due to the excessive curing time in thick sections. Optimum performance in butt joints is obtained when the width to depth ratio of the sealant bead lies within the range 2:1 to 1:1, for elastoplastic sealants (including one or two part polysulphides), or the range 1:1 to 1:2 for plastoelastic sealants (including cross linked butyl rubber).

Sealants should be applied against a firm backing so that it is forced against the side of the joint under sufficient pressure to ensure good adhesion. The back-up material should be resilient and not adhere to or react with the sealant and be of a joint filler material as described above.

We have recently completed an office block where the brickwork is covered in a thick white efflorescence. Is there any way of removing it quickly before hand over?

Unfortunately there is no quick and permanent way to remove efflorescence. It could have been prevented initially by adequately protecting the brickwork during construction to stop large amounts of water entering the uncompleted brickwork. Extensive white efflorescence is usually indicative of ineffective or no protection.

It is preferable to allow the efflorescence to weather away naturally. However it is possible to remove it by brushing with a soft bristle brush. The deposit should be collected and removed so that it does not have the chance to enter the masonry at lower levels if the brickwork becomes wet again. Any deposit remaining may be removed or reduced by sponging with clean cold water.

Chemical methods are not necessary for the removal of efflorescence and are best avoided. Some manufacturers have products that purport to remove efflorescence but we believe they are unnecessary and that the procedures described above are effective and less costly.

We have been told that the brickwork on our house should have a sealant applied to it to prolong its life. We have had a quote, which is very expensive, but we are very concerned that the brickwork will decay very quickly if this treatment is not applied. What are your thoughts on sealants?

We believe the use of sealants and water repellent treatments on brickwork is totally unnecessary and take the view that properly specified and built work performs perfectly satisfactorily in resisting water penetration by wind driven rain, without their need. Brickwork inevitably gets wet in rainy weather and dries out later. This is the way it works and has done so for thousands of years.

Brickwork is a very cost effective facing material that retains its good looks. Many people feel its appearance actually improves with age and requires little if any routine maintenance for many decades. Some repointing of mortar joints may eventually become necessary in very exposed parts of the structure, e.g. chimneystacks.

The application of a surface treatment sacrifices this major advantage. Regardless of whether they are matt or ‘invisible’ finishes they change the natural weathering of facing brickwork, sometimes causing a patchy appearance. They are not permanent treatments, deteriorate over time and therefore would have to be reapplied at some date in the future. This results in an unnecessary maintenance liability and expense.

Furthermore the use of sealants on brickwork can cause problems. They can reduce the rate of evaporation of any water from the wall and depending on exposure conditions, particularly if it has full fill cavity insulation. The quantity of water in the wall may increase because the surface drying is inhibited by the sealant on the face. In certain situations it could be enough to saturate the brick sufficiently for frost attack to occur resulting in spalling i.e. when the brick surface breaks away exposing the soft and porous core of the brick.

If there were problems of water penetration through the walls, a surveyor or builder would be able to identify and correct the cause of the problem which is likely to be a fault in the detailing or construction of the brickwork. Applying a sealant or water repellent treatment to the brickwork is unlikely to correct such defects.

Properly built brickwork will give many years of trouble free service. Waterproof sealant or water resisting treatments has no place as the routine treatment of brickwork.

Our house is only three years old and built of a very beautiful brick that we love. However over the past few years we have noticed that the two courses of bricks below damp proof course level are beginning to flake and erode and it is especially noticeable where our new patio abuts the building. Why are the bricks doing this and what can be done to overcome the problem?

Probably moderately frost resistant bricks (F1 designation) were used on the project and if they remain very wet together with repeated freezing and thawing conditions then frost damage and spalling, i.e. when the brick surface cracks away exposing the soft and porous core of the brick, can occur.

The bricks below damp proof course level may be getting very wet if the adjacent ground is not well drained or your patio drains surface water towards the wall rather than away from it. If it does not, then you could cut the surface of the paving back from the wall by about 100-150mm (4-6 inches) and form a drainage channel filled with pea shingle. Make sure that water getting into this channel can readily drain out at the ends.

By definition an F1 designation moderately frost resistant brick is durable enough for use when detailing on the building protects the brickwork from saturation or near saturation e.g. by roof overhangs an d projecting sills and copings. BS 5628-3: 2005 Code of practice for the use of masonry gives guidance on the selection of bricks and mortars for use when brickwork might be subjected to frequent freezing and thawing when saturated. You can obtain latest version from the BSI.

Generally all bricks are acceptable for work below or within 150mm above ground but F2 designated frost resistant bricks should be used where there is a high risk of saturation with a poorly drained site and freezing may occur.

I want to specify engineering bricks on a project because I believe they will be more durable. They are very dense and will not get so wet, thus preventing them from spalling. Why are there not more buildings built of engineering bricks if they are so durable?

For clay bricks strength and water absorption are not properties that give a dependable indication of frost resistance. More importantly there are many bricks of only modest strength (7-20N/mmî) and high water absorption (20%-30%), which have excellent resistance to damage by frost action. Some bricks of relatively high strength and low water absorption are nevertheless only moderately frost resistant. There is no dependable correlation between strength or water absorption and frost resistance.

The two categories of frost resistance, F2 (Frost resistant) and F1 (Moderately frost resistant), referred to in BS EN 771.1:2005 Specification for clay masonry units are classified by declaration. This is as a result of observation after a number of years in use or sometimes for new products by subjecting them to a specified frost resistance test. You can obtain the latest version from the BSI.

Engineering bricks are classified only by their compressive strength and water absorption. There are Class A engineering bricks that have a compressive strength greater than 125N/mm² and water absorption less than 4.5% by mass and Class B engineering bricks that have a compressive strength greater than 75N/mm² and water absorption less than 7%.

Traditionally they are used in civil engineering applications. They can also be used as damp proof course (DPC) bricks and in the structural design of brickwork to resist lateral loads and large vertical loads. A correlation is recognized between flexural strength of brickwork and water absorption of the brick units.

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The Building Centre, 26 Store Street, London, WC1E 7BT

Telephone: 020 7323 7030
Fax: 020 7580 3795
Email: brick@brick.org.uk

         

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