1.4 Control Joints

1.4.1 General Notes

It is the specifiers responsibility to note on the plans where control joints should be formed, This document outlines suggested locations for vertical & horizontal control joints and should act as a guide. Before commencing work confirm the layout of control joints and other visual detailing of the finished work. Control Joints must be reflected through final coating. Any substrate that has been installed by a separate contractor to the plasterer/applicator shall be responsible for ensuring that any control joints are in place according to the substrate manufacturers specifications. Defining the location of control joints in a generic form is not easy because each building creates a unique situation. While control joints are an ideal method they are limited in providing a path for relief. In some cases further action may be required, please refer to an engineer or architect for further information. Installation of control joints in the following suggested locations will minimise the chance of cracking occurring by relieving actual & potential stresses on the wall surface due to various conditions but not limited to the following;

  • Thermal expansion and contraction differentials between dissimilar materials, Geological movement or settlement.
  • Engineered flexibility in the design of the building.
  • Vibration barriers between areas holding heavy equipment or subject to vehicular traffic vibration.

1.4.2 Types of Control Joints

Typical Control Joint (negative detail)

This is where a break in the cladding is located. Where the structure is timber/steel framing the control joint will generally be a proprietary PVC flashing.

Expansion/Structural Control Joint

A Expansion/Structural Control joint is where there is a break between the underlying structure. On a timber/steel framed house this can be formed by having two studs next to each other which are not attached to each other. with a break in the top and bottom plate. These types of joints are generally found on larger projects and there centres need to be determined by a structural engineer, the fixing either side of the control must be no less than 50mm and no greater than 100mm.

Expressed Control Joint

An expressed joint is where the control joint is carried through the surface of the plaster only, these are not a replacement for a Typical Control Joint, instead they are used in small areas where there is a chance of hairline cracking.

Drainage Movement Joint

A Drained Movement Junction ( DMJ ) allows for the egress/removal of any moisture that may penetrate the control joint. If a control joint is penetrated or breaks down, any incidental moisture that passes beyond the joint is deflected & removed from the cladding system without affecting other building components. Creating a DMJ is a relatively straight forward process when combined with standard Resene Construction Systems' Control Joint details. Most vertical & horizontal control joints finish into a proprietary uPVC starter track or head flashing, it is at these junctions or interfaces that allowance must be made to create a DMJ. There is no point providing a control joint that minimises potential cracking issues yet creates another problem that the control joint isn't designed to do. By this we are referring to the ingress of moisture through a control joint junction that doesn't allow drainage to the outside of the cladding. You can easily create a DMJ by checking/cutting out the pvc front & underside of the starter track/Head Flashing, this allows a clear drainage point for surface water to clear the cladding. Inter-storey drainage joints must be provided for walls over two storeys or 7m in height in accordance with the requirements of NZBC E2/AS1

Retrospective Control Joint

A retrospective control joint, is a control joint that is installed in a system after the plastering has been carried out. A saw cut is placed through the render system and should be no greater than 15mm deep into the substrate. A PEF Backing Rod will then be installed into the joint. Depending on what stage the render is at will determine how this is finished. If the surface of the render is to be painted you would mask either side of the control joint and seal and paint accordingly. If the surface of the render needs to be painted you must seal the control joint and paint the surface accordingly. Retrospective control joints are common in Masonry Substrates where it is easier to cut in a control joint after the rendering has been completed.

1.4.3 Control Joint Locations

General Locations (required on all substrates)

There are some typical locations for control joints as noted in 1.4.2, these should be installed where ever the following occur.

  • Where columns intersect beamwork control joints should be formed so that they are running vertically and horizontally of the intersection
  • Large doors & windows ie Ranch Sliders, & Bi-Fold type where the window area is greater than 8.0m2
  • Junctions between dissimilar materials, ie Masonry to Resene Construction Systems EPS/XPS System
  • Where there are small widths of plaster (ie. less than a trowel width)

EPS/XPS Substrates

  • Where the wall length is greater than 8 metres in length a control joint will need to be installed
  • Where a two storey dwelling wall height exceeds 6 metres a horizontal control joint is required
  • Control Joints are required at all interfloor levels on multi-level construction (eg. 3 or more floors)

Integra AAC Panel

  • Where the wall length is greater than 8 metres in length a control joint will need to be installed
  • Where a two storey dwelling wall height exceeds 6 metres a horizontal control joint is required
  • Control Joints are required at all interfloor levels on multi-level construction (eg. 3 or more floors)

Clay Brick and Masonry Substrates

  • If the brick/block wall is being continuously rendered over the foundation then a control joint must be installed, typically a Retrospective Control Joint is the best solution.
  • Where a inter-floor slab sits on top of the blockwork and is exposed then a retrospective Control Joint will need to be installed where the block meets the slab, this applies to the top and bottom edge of the slab
  • Control Joints must be installed in accordance with NZS 4229 Section 13, block/brick manufacturer, construction specification and/or engineer's requirements.

ICF Blocks (polyblocks) Substrates

  • A control joint must be installed 50mm below the floor slab level, this control joint must carry right the way through to the concrete core of the ICF block.

Proprietary Substrates (eg. Fibre Cement Boards/Sheets, AAC)

  • The substrate manufacturers specifications must be followed
  • It is the builders responsibility to ensure that the appropriate allowances for control joints are in place

1.4.4 Important Notes/Considerations

  • Control Joints should never have mesh carried over them (unless it is being cut through afterwards)
  • Should be a minimum of 6mm in width and  be reflected through the coating (ie. should not be textured over)
  • Control Joints should follow the substrate manufacturers specifications
  • Where a Resene Construction Systems Horizontal Control Joint meets a external corner flashing it must extend through this
  • Where a Resene Construction Systems Vertical Control Joint Flashing meets a Starter Strip or Head flashing a Drained Movement joint must be formed
  • Where a Vertical Control Joint meets a Head Flashing or Starter Strip a break in those flashings should occur.
  • Where you have a control joint on one side of the structure try and reflect this control joint in a similar place on the opposite side of the structure

1.4.5 Examples

Vertical Control Joint with a Decorative Mouldings

When you install any control joints you will need to make sure the control joint has been installed correctly. Particular care needs to be taken if you are installing a decorative moulding over the top of the control joint. Where you have a control joint running vertically and a decorative moulding is installed over the top of the control joint

  • Make sure that there is either a physical break through the moulding if the moulding is extending more than 150mm past the joint

or that

  • the moulding is left floating if it is extending less than 150mm past the Control joint. In this situation the area of moulding less than 150mm is not fixed to the cladding instead it is sealed around the moulding edge.

Vertical Control Joint meeting a Sill/Jamb Junction

Where a vertical control joint meets a sill/jamb junction care must be taken that the control joint will not flex and move at a different rate to what the window edge may move at, therefore the control joint must extend through the window flashings. To acheive this the following process must be carried out.

  • Window Flashings are installed if required by the Resene Construction Systems Cladding/Render system
  • The control joint flashing is installed if required by the Resene Construction Systems Cladding/Render System
  • The window flashings should be mitred/checked out where the control joint intersects the window flashing
  • Plaster as per usual
  • After texturing is complete scribe out the corner between the sill and jamb to the same width as the control joint which is meeting this area, care must be taken so that damage is not caused to any underlying soakers or membranes
  • Seal this control joint location area and paint it.

What this achieves is a flexible control joint location so any movement in the wall is not only allowed for in the vertical control joint, but also through the window sill edge.