Block Work

7/21/2019 Block Work

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Advantages of using blocks below ground level

The benefits to the builder of using blocks below ground are:

• Speed of build.

• Lightweight and safe.

• Less waste as blocks can be cut accurately.

• Lower cost.

Independent tests by Architects and Charted Surveyors have shown that you can build

foundations at least twice as fast by using trench blocks and four times as fast as building

with common brick.

Blockwork foundation and insulated cavity wall

This form of construction incorporates a blockwork foundation below ground level with a

traditional brick and block cavity wall above.

The cavity can be partially filled or full filled as required. This type of construction offers a

structure with good sound and thermal insulation qualities.

FOUNDATIONS AND BLOCKWORK BELOW GROUND LEVEL

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Solid blockwork foundation and insulated cavity wall



Block cavity wall foundation

This is an alternative solid block foundation construction. The blocks below ground level are

laid to form a cavity which is then filled up to ground level with a cement/aggregate mix.

The cavity can be partially filled or fully filled as required.

FOUNDATIONS AND BLOCKWORK BELOW GROUND LEVEL

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Hollow cavity wall with a blockwork foundation



Building with solid and hollow blocks

Blockwork has become a very popular quick method of building external and internal walls. The

combination of moisture-resistance, strength and thermal insulation qualities makes it possible

for blocks to be used for a wide range of external and internal wall solutions for all types of

buildings ranging from traditional domestic dwellings to commercial and industrial units.

Apart from the size of the blocks the building operations used to erect walls are the same

as for brickwork.

However, there are a number of constructional factors to consider when building with

blocks to achieve a satisfactory standard of finish and to maintain stability within the wall.

Some of these factors are:

• Never mix different types of blocks in the same run of walling, and do not use common

or facing bricks as closers as they will reduce the thermal and sound insulation qualities

of the blockwork.

• Always set out the first course dry so that the position of cut blocks can ascertained and

any adjustment to the width of joints can be made to achieve and maintain a bond within

the wall.

• Use only specified mortar mixes and ensure that bed and cross joints are solidly filled.

• Care should be taken to maintain gauge to correspond with brickwork gauge.

• Care should be taken when laying heavy blocks as they tend to settle, causing the wall

ties to slope down towards the inner leaf increasing the risk of water penetration.

• The process of building with blocks is much quicker than building with bricks. Since the

blockwork rises more quickly, the weight of the blocks causes the fresh soft mortar bed

to be squeezed out resulting in a wall that can be deformed and out of plumb.

• The blocks should be tapped down to compact the joint and ensure the wall is plumb.

Do not tap blocks sideways to bring them to plumb as this tends to open a gap on one

side of the bed joint causing the block to wobble.

BLOCKWORK CONSTRUCTION

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Bonding

Blocks are available in many shapes and sizes and therefore there are many different

bonding arrangements possible.

When setting out a bonding arrangement for a particular wall, there are certain building

principles that should be followed:

• The blocks should be laid to a regular bond, usually half bond where possible.

• Under no circumstances should the blocks be laid to a bond of less than a quarter bond.

• Take care that broken bond is no less than quarter bond. If less and particularly if close

to a reveal, the vertical line of the potential weakness may result in shrinkage cracking.

• There will be occasions when the wall length does not work to full block sizes, but it is

essential to avoid close laps of joints. Always ensure that a lap of at least 100mm exists.

Joints that are closer than this can result in vertical cracking.

• Corners may be bonded by cutting standard blocks or by using quoin blocks.

• Wall junctions are normally bonded, or ties can be use with a straight joint. Butterfly ties

should be used where vertical differential movement may occur.

• If it is not convenient to build a junction wall at the same time as the main wall, some

provision must be made to allow the junction wall to be bonded to the main wall. Indents

may be left to allow bonding to occur at a later stage.

• Bonding should be set out so that lintels bear preferably on a whole block. If this is not

possible, a minimum two-thirds length block is acceptable but definatley not less.

• Lintels should normally bear by at least 150mm.

• Some types of hollow and cellular blocks may need to be filled under lintel ends to

provide sufficient bearing strength.

• Course heights must be checked regularly with a vertical gauge rod as work proceeds.

• Gauge should normally be equivalent to three courses of metric bricks.

• In windy weather, block walls should be restrained by temporary propping.

• In windy weather, the day work lift height may be reduced as an alternative to propping.

• Blocks should be kept dry before use.


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Normal half bond

Badly placed broken bond creating a vertical weakness in the wall

Lintel bearing on a whole block

Bonding in blockwork

Cut blocks

Lintel bearing on

a whole block




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Bonding quoins and junctions

Purpose-made quoin return block

Quoin bonding with cut block to form half bond

Alternative method of quoin bonding using coursing blocks



Bonding quoins and junctions


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Bonded ‘T’ junction

Bonded ‘T’ junction using a straight joint and wall ties



Building walls in solid or hollow blocks

External walls

One of the primary functions of an external wall is to provide an efficient weathershield

to prevent the penetration of moisture which can have a detrimental effect on the internal

structure of the building. The high moisture resistance of some building blocks makes them

ideal for the construction of inner and outer leaves of external cavity walls as well as solid

external walls.

When used as an inner leaf they can be combined with bricks, stone or timber framing as

an outer leaf with the cavity partially or fully filled.

When used as an outer leaf they can be used as a single solid thick block or with an inner

leaf constructed also of blocks. In some cases the inner leaf may be constructed of timber

to form a timber frame.


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Typical cavity wall construction using facing bricks and blocks



Closing cavities of external walling built with blocks

With all cavity walls it is essential that the cavity be closed at reveals to openings such as

door and window openings. This can be achieved by using cut blocks or by using special

reveal blocks manufactured for the purpose.

The diagrams below show the two methods.


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For bonding purposes, three courses of brickwork are equal to one course of blockwork.

This makes bonding simple as long as both bricks and blocks are kept accurately gauged.

Closing cavity using cut blocks Closing cavity using reveal blocks



Junctions walls

The diagram shows a typical method of constructing junction walls.


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Junction wall construction for cavity walls

Inserting wall ties into cavity walls constructed of brick and block



Bonding using cut blocks, special blocks or coursing bricks

To maintain bond within a wall it may be necessary to use either coursing bricks or blocks

of quarter, half or three-quarter size which have been cut from a whole block, or special

blocks manufactured to those sizes.

These blocks are integrated into the walling bond at junctions and over openings in the wall.

Ordinary facing or common bricks should never be used for this purpose.


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Typical use of cut and course blocks to maintain bond

Coursing bricks



Internal block walling

One of the most common uses of building blocks is for the building of internal or partition

walls. Partition walls can either be of solid or cavity construction. When used as a partition

wall, the blocks can reduce sound transmission between rooms as well as providing

excellent thermal insulation between rooms. They also provide a secure fixing for shelves,

radiators and other fixings.


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Internal wall of cavity construction

Internal wall of solid construction

Solid internal partition wall

Plaster or smooth faced finish

Cavity partition wall

Smooth

faced blocks

Internal plaster

Block Work

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