fyfestone tech movement control

8/3/2019 Fyfestone Tech Movement Control

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MOVEMENT

CONTROL


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Movement joints are used to eliminate or

control cracking within the fabric. The joints

are located in strategic positions and allow

slight, predetermined movement without

subsequent cracking to the masonry. Spacing,

design and location of movement joints depends

principally on the dimensions and shape of the

wall in question, detailing techniques and the

complexity of the structure. The joints should be

located at junctions which may be vulnerable to

cracking.

The position of movement joints will be strongly

influenced by structural and architectural

considerations but the following may prove

useful as an indication of where control joints may

be necessary.

MOVEMENT

CONTROL


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1. Cracking is most likely to occur in long straight walls.

Blockwork walls of excessive length should be divided into a

series of rectangular panels with movement joints between

each panel. The effects of end restraint need to be assessed

when deciding on the panel length. This can add either

25% or 50% to the actual length if one or two ends are fully

restrained. It is upon this total length that the empirical

rules are then applied. In the case of Fyfestone blocks,

the maximum length between movement joints is 9m.

The length of each panel should not normally be in excess of

twice the height of the panel and areas of blockwork above

and below openings should be treated as individual panels.

The data below is a general rule of thumb for methods ofcontrolling movement in blockwork panels.

2. Movement joints should be provided where changes of

height, thickness and profile (either on plan or section) occur

in the wall, since these junctions are particularly vulnerable

to cracking.

3. Control joints will be required at the junctions of intersecting

walls and junctions with columns, and also where walls arepenetrated by major service pipes and ducts, or where large

chases are incorporated to accommodate services.

4. A number of factors should be considered by the designer

when using Fyfestone:

providing control joints at suitable centres

using bed-joint reinforcement

protecting the blocks before and during construction

specifying the correct mortar

Detailed information is covered within BS5628: Part 3:

Control joints are vertical separations built into a wall and

located where cracking may occur due to excessive stresses

caused mainly by drying shrinkage.

As a general guide, the joints should be at regular spacing up

to 9m in external and internal walls.

It should be noted that on south and east elevations,

the effect of the early morning sun on these faces can

raise the temperature very rapidly and cause greater

movement to take place than elsewhere in the structure. It

is recommended that the above rules be strictly adhered to

unless further advice is taken.

Control joints may also be required at:

changes in wall height and thickness.

junctions with other forms of construction e.g. steel

stanchions and reinforced concrete columns

intersections with other walls and partitions particular

attention should be given where return walls occur.

return angles in L-, T- and U-shaped buildings.chases or recesses for piping, pilasters, fixtures, etc.

movement joints in roof and floor slabs. These joints

in the main structure must be continued through the

wall construction. The width of the wall joint and the

compressible filler should be similar to that used in the roof

and floor slabs.

one or both sides of some large wall openings, e.g. windows,

louvres or doors. However, the addition of localised bed-joint

reinforcement above and below openings can often

eliminate the need for control joints.

FORMATION OF CONTROL JOINTS

The wall is built in the normal half bond manner with the

exception that on alternate courses, half-length blocks are

used to form a straight vertical joint.

The sealant should be one of the following or similar:

an acrylic based sealant

two-part polysulphide

a silicone-based sealant

Internally, the joint should be left open as long as possible to

enable the wall to dry out thoroughly. Control joints should

be carried through all finishes. In cavity walls, the control

joints in each leaf should be offset. The flexibility of the cavity

ties is normally sufficient to compensate for the very small

differential movement between two leaves. Generally, the

joint spacing is greater on the inner leaf so the staggering of

joints is relatively simple.

TECHNICAL DATA

LENGTH TO HEIGHT RATIO OF PANEL (L:H) > 2:1 > 2.5:1 > 3:1 > 4:1

SPACING OF CONTROL JOINT (architectural masonry) 69m 69m 69m 69m

SPACING OF BED JOINT (reinforcement (mm)) 600/675 400/450 200/225


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HORIZONTAL CONTROL JOINTS

Limitation on uninterrupted height when the method of

limiting the uninterrupted height is adopted in accordance

with BS 5628 : Part 1, the outer leaf should be supported

at intervals of not more than every third storey or every

9m, whichever is less. This method employs shelf angles

and vertical joints, which subsequently provides a meansof vertical movement control. However, for buildings not

exceeding four storeys or 12m in height, whichever is less;

the outer leaf may be uninterrupted for its full height.

MOVEMENTS DUE TO THERMAL EFFECTS

In general, movements due to normal changes in

temperature of internal walls are likely to be small and not

an important cause of cracking. However, in long walls or

partitions where variations in temperature are likely to be

large, care should be taken to accommodate movement.

MOISTURE MOVEMENT

All concrete units shrink slightly after manufacture

but part of this shrinkage is reversible due to dry units

expanding slightly when wetted. However, care should

be taken to ensure that all units comply with the relevant

European Standard for drying shrinkage requirements.

To minimise moisture movement, all masonry units should

be kept as dry as possible prior to laying and when laying,

they should not be soaked in order to adjust the suction for

the mortar.

DIFFERENTIAL MOVEMENT

If practical, products with different characteristics should

not be rigidly bonded together. Thus clay and concrete unitsshould not be mixed unless consideration has been made

into allowing independent movement.

All concrete products shrink slightly over a period of time,

the initial shrinkage taking place during the first six months

to a year. Likewise some clay bricks built on top of concrete

brick plinth walls may cause severe cracking in the plinth

wall. Where dissimilar materials are used, for example in

cavity walls, it is good practice to avoid the use of rigid ties

and permanent bonding together of brick or block work with

the opposing component.

PRECAUTIONS

Procedures to minimise cracking:

1. Use the correct grade of mortar: an unnecessarily strong

grade of mortar will concentrate the effects of any

differential movement on few and wider cracks. A weaker

mortar will accommodate small movements so that any

cracking will be distributed as hair cracks in the joints where

they are less noticeable

2. Bonding: cracking of masonry is more likely to occur if bond

patterns are not maintained and alignment of vertical joints

results. This can be exacerbated by poor workmanship

3. Use masonry of low potential shrinkage. Ensure that the units

are dry before use and during laying

4. Reinforce the masonry with joint reinforcement at locations

of high stress

5. Allow for thermal and shrinkage stress by the correct

incorporation of control joints at appropriate intervals

Joint design should comprise a sealant cover either side

of the joint with compressible joint backing. The choice

of sealant is important. Fyfestone recommend the use

of sophisticated sealant such as two-part polysulphides

or acrylic resin polymers. The former is the most proven

performer.

The need for periodic maintenance of joints should be

recognised and considered when positioning joints.

LOCATION OF MOVEMENT JOINTS

Movement joints in masonry may either be expansive or

contraction joints; the latter being free to accommodate any

tensile stresses. The incorporation of movement joints within

a wall structure should be in accordance with

BS 5628 : Part 3: 2005.

Movement joints should be installed at not greater than 9m

centres and may be formed as a straight butt joint. Or in a

toothed fashion in the coursework using a separate medium,

such as dpc material, and subsequently pointed in a suitably

coloured mastic. Flexible damp proof courses may also be

used to act as a slip planes between materials of different

properties.

Care should be taken to ensure that all movement joints also

comply with the requirements of the other functions of the

wall, ie. lateral restraint, fire resistances, etc.

In estimating the correct spacing of movement joints, it is

best to design walls of concrete units into a series of panels.

Areas above and below windows and doors should be

treated as individual panels except where it is permissible to

control cracking by the use of bed reinforcement.

Generally the shape of the panels is critical in deciding the

susceptibility to cracking. It is more likely to occur if thelength exceeds about 1.5 to 2 times its height.

Care should be taken that there is no excessive end restraint

and if lateral stability is likely to be affected then dowels, one

end of which is not fixed, should be used to provide stability.

WALL TIES

Wall ties should conform to BS EN 845-1. For guidance on

selection and use of wall ties see BS 5628 : Part 3 : 2005.


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TYPE OF MOVEMENT JOINTS

Expansion Joint

Contraction Joint Internal

Contraction Joint Internal and External Where wall is penetrated by large duct or services

EXAMPLES OF WHERE MOVEMENT CONTROL JOINTS

COULD BE LOCATED


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Joint hidden by downwater pipe

At junction of columns, etc.

Expansion joint in floor slab

At staggered joints in a cavity wall

Junction of steel frame

EXAMPLES OF WHERE MOVEMENT CONTROL JOINTS

COULD BE LOCATED (continued)


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At window opening

CONTROL OF CRACKING USING REINFORCEMENT

If it is impractical to divide walls into a large number of

panels because of, for example, a large number of openings,

then reinforcement can be introduced to distribute the

areas of high stress. It is still important to maintain panel

length/height ratio at 22.5. The reinforcement should be

long enough, or have enough overlap, to distribute stressesadequately and be provided with the correct cover. All bed

joint reinforcement must be used in accordance with the

manufacturers recommendations.


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SALES OFFICE ENGLAND and WALES

North End, Ashton Keynes, Wiltshire SN6 6QX Tel: 01285 646801 Fax: 01285 646857

SALES OFFICE SCOTLAND and IRELANDKemnay Quarry, Aquithie Road, Kemnay, Scotland AB51 5PD Tel: 01467 651000 Fax: 01467 642342 Email: [email protected]

www.fyfestone.com

An AGGREGATE INDUSTRIES Business

Aggregate Industries UK Ltd pursues a policy of continuous product improvement and accordingly reserves the right to vary designs and specifications without notice.

FYFESTONE is a registered trademark of Aggregate Industries UK Ltd.

Whilst every effort is made to ensure the accuracy of content, both written and pictorial, interested parties should contact Aggregate Industries (the Company) for verification.This datasheet and any advice is provided by the Company free of charge and is accordingly on terms that no liability of any kind (including liability for negligence) will attach to the Company or its

servants or agents arising out of or in connection with or in relation to this data sheet or any such advice.

fyfestone tech movement control

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