Design - Movement Control

Under normal circumstances, masonry constructions will experience some movement associated with drying shrinkage, thermal expansion and contraction. This can be easily accommodated by using suitable methods.
 
Calculating exact movements is not feasible in practice and therefore several rules of thumb have been established for masonry construction which has been proven to work in practice over many years.
 
 

MOVEMENT JOINTS

Internal walls of low-rise dwellings and houses do not normally require movement joints and the use of bed joint reinforcement is usually sufficient. Movement joints are not normally needed below dpc. Movement joints are particularly suitable at intersections of dissimilar materials, at intersecting walls for example.
For acoustic separating and party walls, vertical movement joints should not be used.
 

General Guidelines:

  • Airtec blockwork should be divided into approximately 6m long panels.
  • Each panel should be separated by a suitable vertical movement joint placed in unobtrusive locations (note: not to be used in acoustic separating or party walls).
  • The first movement joint should not be more than 3m distance from an internal or external corner / angle.
  • Adverse effects of movement can be minimised by protecting from extremes of moisture before, during and after construction. Recommendations can be found in BS 5628: Part 3: 1985 clause 20.
  • Over strong mortars should be avoided to reduce the effect of movement.
  • Movement joints can be formed by butting up the Airtec blocks against a 10mm strip of rigid filler which is left in place until the wall is finished. This can remain in place or be removed. However, additional sealing is recommended to achieve adequate air tightness.
  • Stop beads should be used at the ends of the joint.
 

BED JOINT REINFORCEMENT

Bed joint reinforcement is particularly suitable for houses and low rise dwellings and wherever a vertical movement joint may not be aesthetically practical. Reinforcement laid on horizontal beds is particularly suitable for areas of high stress. For example, under concentrated loads such as loadbearing joists or beams and at openings around windows and doors.
 

General Guidelines:

  • The reinforcement should extend at least 600mm into adjacent blockwork.
  • Ideally the reinforcement should be of a suitable length so that any stresses are transmitted to movement joints or adjacent areas of blockwork.
  • Reinforcement should normally have a mortar cover of at least 13mm on the face of the internal blockwork and 25mm on the external faces.
  • Where a wall is supported by a floor, the first two courses above the floor junction should be bed-joint reinforced.
  • Masonry grade reinforcement should be used. Plastering grades are not suitable.
 

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