Materials - Repair and maintenance Unit 302

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Level 3 Diploma in Bricklaying

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Unit 302: Repair and maintain masonry structures

Materials



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IntroductionSession aims

By the end of this unit you will be able to:

•describe the application of common materials used in masonry maintenance.



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Introduction

The majority of housing stock in the UK was built before 1930 and has become very dated. It is therefore necessary to be familiar with older building methods to enable reparation work on older buildings that does not to ruin its appearance or effectiveness. Indeed, the ability to carry out repairs on a building that match closely its existing features.

In addition to this, some home owners will want to carry out alterations to their properties to improve them, possibly by adding extra space or by changing the current layout of the existing building.

In order to carry out work effectively you will need to have a good understanding of the building materials used to repair masonry.



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Getting started

Lets take a look at your current knowledge of this area. See how many defects you can spot in this picture, focussing in particular on building practice and choice of materials.

© Shuttesrtock | Peter Guess



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How did you get on?

Bad brick colour match

Uneven sized bed joints

Brick bat too small

Oversized joints

No lintel?

Mortar looks very strong

Mortar stains on wall

http://1.bp.blogspot.com/-168ibqYrMgQ/Uhlo-25uA8I/AAAAAAAABFI/fbOEj-G2udc/s1600/058.JPG



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Materials used in masonry maintenanceWater saturation is the common denominator in most of the defects examined in this unit.

Given the weather in the UK it is inevitable that bricks will remain saturated for long periods of time.

Features that are particularly vulnerable are retaining walls, chimneys stacks, garden walls and parapet walls. All of these areas are exposed to the rain or can become saturated due to contact with the ground.

It is possible, however, to avoiding many of these problem by selecting the correct materials and building in features that will protect a building from the elements. They include corbels and oversailing courses, roof overhang, sill bricks, DPC and flashings.



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Types of Bricks

Common

Engineering

Facing

Used in areas where appearance is of secondary importance (eg internal walls, bricking in openings).

Have low porosity rates.Used mainly underground or where brickwork is exposed.

Mainly used where an attractive appearance is required.

© Shutterstock | Windu

© Wickes.co.uk

© Wickes.co.uk



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Brickwork applicationsCommon bricks Facing bricks

Can be used to match to existing.or where being covered over withrender.

Ensure correct size and colour match when repairing against existing work.

© Shutterstock | Peter Guess



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Brickwork applicationsEngineering bricksUsed below ground or where exposed to severe weather conditions. Engineering bricks have low water absorption rates. Many companies now manufacture class-B facing bricks that can be used to match existing facing bricks.

© matthouldsworth.com © Shutterstock | Artazum



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Brickwork applicationsReclaimed bricksMany reclamation yards will stockreclaimed bricks that can be used on many renovation projects where brickwork needs to be matched to the original specification.

They are generally softer than newer bricks and therefore easier to cut. This can be an advantage if you are repairing curved walls or gables for example.

© Shutterstock | Wheatley



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MortarMortar is made from fine aggregate (sand) and a binding agent (cement). When mixed with water a chemical reaction called hydration occurs, which causes the mortar to set.

Mortar is important for a number of reasons:•It helps to distribute the loads through a wall.•It helps to seal the wall against water ingress.•It helps to compensate for the variability of brick size when laying brickwork.

PlasticisersLiquid plasticisers are sometimes used instead of lime. They work by adding air into the mix, making the mortar more workable by reducing the friction between particles. It can, however, reduce the strength of the bond between the bricks and mortar.



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The use of limeAlthough many modern mortars use cement as the binding agent, lime should be added to improve the mortar’s workability, adhesiveness and resilience against moisture and thermal movement.

Mortar should typically be slightly weaker than the bricks because this increases its ability to resist the stress imposed by movement. A strong mortar mix will not allow movement, meaning that any cracks will occur along the bricks. Strong mortar mixes may also shrink and crack, which can cause spalling.

Normal drinking water should always be used for mortar. Sea water contains salt, which can increase the risk of efflorescence.

© Shutterstock | AdStock

© Shutterstock | Hxdbzxy

© Shutterstock | AdStock



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Application of mortar for repairing brickworkWhen preparing mortar, it is always best to mix a small sample first to match the finished colour in the existing wall. Choose the mortar mix to suit the types of bricks that you are replacing.

Under normal conditions, a 1:1:6 (cement:lime:sand) mix is generally acceptable. But for softer-type of facing bricks, a 1:2:9 mix is usually satisfactory. For very hard, dense bricks used in situations of extreme exposure, a 1:¼:3 is best.

With stronger cement mixes, watch for possible shrinkage of the joint, which could lead to hair-line cracking at the brick–mortar interface.

When re-bedding bricks, apply plenty of mortar along the top of the brick to achieve a full joint and to maintain the compressive performance of the wall.



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Application of blockwork• Wherever possible, blocks should be protected onsite from frost,

rain and mud splashing by wrapping them in protective sheeting.• Blocklaying should not take place in heavy rain unless the blocks

are protected.• Damaged and cracked blocks should not be used.• New blockwork should be protected overnight against the weather.• Blocklaying should not be carried out when the temperature is

below 3ºC.• Do not complete blockwork to a height of more than 1.5m in a day.• When setting out, provide a full block bearing at lintels wherever

possible.

© (All) TravisPerkins.co.uk



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Application of stoneworkRepairing stonework •Assess the damage and repair only what is necessary.

•Find the right match.

•Remove the damaged stone by chopping out the mortar joint with a comb or plugging chisel.

•Cut the new stone to shape, ensuring that you get the same-sized joints as are in the original walling.

•Relay stone and form joint finish. Remember to dampen the surrounding wall to ensure a good key and to allow the mortar to cure properly. Remember also to lay sedimentary stone horizontally along its natural bed line.

© (All) oldhousejournal.com



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Application of concrete

Reinforcing

Concrete is strong in compression but weak in tension. Therefore, reinforcing will need to be placed into concrete at certain times. This will be specified on site by a structural engineer. Reinforcing must always have a suitable cover of concrete on top of it to protect the steel from rust. Spacer bars can be placed underneath the reinforcing to keep it off the floor.

Compacting concrete

Newly placed concrete should always be compacted. This is done to remove any excess air that becomes trapped in the mix. As a general rule for concrete up to a thickness of 100mm, a manual hand tamp can be used. For deeper layers of concrete a vibrating poker can be used.



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Application of concreteCuring concrete

To allow concrete to achieve its maximum strength it needs to be cured after laying. This is done either by spraying the concrete with water after it has initially dried or covering with a plastic sheet to prevent water from evaporating too quickly.

Concreting in extremes of weather

Concreting should not be carried out in temperatures of 2ºC or lower. Retarders can be added to the mix to prevent concrete drying too quickly in very warm temperatures.



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Forming a finish

Forming a neat finish requires good timing; the concrete should be neither be too wet or too dry. Look at the finishes below and see if you can name them.

© hss.com© Shutterstock |Wuttichok Painichiwarapun

© Shutterstock/Jiggo_thekop

© Shutterstock | Witsanu Keephimai

© hss.com



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Forming a finish

The answers are:

Power float Smooth with bull floatWood or plastic float

Brushed and edgedPaved look usinghalf-round jointing iron



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Other materials used in repairing masonry structures

Cavity wall ties

DPC

Piers and cappings

Timber ©TravisPerkins.co.uk

©TravisPerkins.co.uk





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Special bricksFlashing

Insulation Lintels

© TravisPerkins.co.uk

© Wickes.co.uk

© [email protected]

© Shutterstock/wavebreakmedia



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Any questions?

Materials - Repair and maintenance Unit 302

Education

Transcript of Materials - Repair and maintenance Unit 302