Movement Joints or Expansion Joints are installed in buildings as the name suggests to prevent cracks developing or alleviate the potential for masonry to crack through thermal expansion and contraction. Hence in the Norhern hemisphere it is likely that most movement will occur on south facing walls because they receive the most sun. Movement Joints should be installed in long runs of wall at 6.0 to 9.0m spacing depending on the type and location of material used.
In the example below cracks have appeared in a large detached rendered property less than three years old beacause; a) the blockwork substrate was built with relatively 'green' blocks that had not been alowed to dry out properly before being used, followed by a rapid overcoating with concrete render; and b) wall lengths are exceeding 6.0m without a break in construction.
In the intervening period the blocks have gradually dried out and shrunk combined with thermal movement resulting in cracks to the blockwork and rendered surface finish. Apart from being aesthetically undesirable the cracks provide a pathway for moisture ingress, increasing the potential for further delapidation and reducing the buildings thermal efficiency.
To alleviate stresses and hence further cracking we installed a Movement Joint in the outer skin of the cavity wall to Thor Helical Remedial standard method TMJ-01 with the extension of slip ties into Crack Stitch to pick up large cracks. Following completion of the movement joint installation all walls are rerendered with a proprietary polymer modified cement render and acrylic based finish coat to hide the slip tie and crack stitch installation.
The following example of a solid wall construction joint was installed to provide a degree of flexibility between two buildings that had suffered from structural rather than thermal movement.
The property is located at the end of a terrace of four Victorian cottages. At some point not long after the original development and additional cottage was added by 'butt jointing' to the north east gable of the terrace. The addition is on a gently sloping site that falls away to a river some 100m away. Construction is solid wall in mainly soft Norfolk Reds with slightly harder buff bricks forming architectural features all set in a traditional lime mortar. The two properties were combined some years ago to form the building seen today. A modern Utility / Kitchen extension was built onto the rear elevation some 20 years ago and all structures are clad in traditional red clay pantile.
The owners had commissioned an Engineer's Survey / Report but this was not made available for inspection. From our visual inspection it was evident that the later Victorian addition had rotated away from the original terrace. The result of this movement has ben that the butt joint between the two structures has opened up ranging from 10mm at ground level to 50mm at eaves level on the from elevation, and correspondingly from 10mm to 35mm on the rear elevation. The rotational and 'pulling' effect had created further cracks between ground and first floor windows on the front elevation, and internally producing cracks in plaster finishes at first floor landing level in what would have originally been and external wall.
It was evident that the movement had been a historical and ongoing problem with unsympathetic cement patch repairs to construction butt joints and brick bed joints. Engineering 'tell-tale' studs were also evident on internal plaster finishes within the first floor landing walls. Cause of the movement had been established as a leaking surface water drain on the gable / front corner which had subsequently been repaired. Our remit was to re-introduce some structural integrity to the building whist providing a certain amount flexibility to accommodate any possible future movement.
Our repair strategy involved removing all traces of cement infill to the front and rear butt joints and installing movement joints to Thor Helical standard method TMJ-02. To accommodate the variation in width and to disguise the joint a lime mortar pigmented to match the buff bricks of the architectural feature. The joints were then finished with buff coloured mastic to provide a uniform with for the construction joint and blend in with existing brickwork.
The weakened panel of brickwork between ground and first floor windows was reinforced with a Masonry Beam and Crack Stitch which were extended to coincide where possible with slip ties of the Movement Joint to provide some continuity between them. Internally, cracks were reinforced with Crack Stitch and plaster finishes made good ready for redecoration by others.