Civil Engineering Reference
In-Depth Information
Case study
External tiling failure on a health service building
The BRE Advisory Service was invited to
establish the reasons for an external tiling
failure. The building was concrete framed with
blockwork or brickwork infill panels. The
external wall tiling had been fixed to a render
backing with a thin bed adhesive. Cracking,
loss of adhesion and deterioration of the tiling
had occurred some 15 years after the
building had been completed.
The external tiling had cracked and the
render coat had bulged away from the
background (Figure 9.6) at the south-west
corner. Away from the corner, tiles mainly
were intact and still adhered to the
background. The first movement joint was
7.5 m from the corner and then at 6.75 m
spacing (the column positions).
coping, and there was some frost damage.
The render backing to the tiles taken
from the area where the tiling had become
detached was analysed for sulfate content.
The amount of sulfate, determined as the
percentage of sulfur trioxide, was 3.5%. In a
mix of 1:1:6 cement:lime:sand;
approximately 0.3% sulfate would normally
be expected if ordinary Portland cement
was used in the mix. The sample was also
analysed using differential thermal analysis,
which showed there was a significant
amount of ettringite present. The common
bricks used as the base for the render
backing to the tiling contained sufficient
soluble salts for the reaction to occur.
The major cause of the failed tiling was
sulfate attack in the brickwork mortar and
render backing to the tiling. There was
considerable evidence that rain had
penetrated through the tiling and entered
the render and brickwork background; this
was shown by the stalactites on the soffit to
the walls at ground level and salt deposits
and staining of the concrete columns. The
external wall tiling had not formed an
impervious cladding to the building and rain
ingress through the tile joints had occurred.
Some of the cracking in the tiling could
be attributed to insufficient movement
joints, particularly at junctions with
dissimilar materials (ie between the
brickwork and concrete columns).
It was doubtful if it would be possible to
repair or replace the existing tiling. It was
possible the building could be overclad with,
for example, profiled sheeting, glass
reinforced plastics panels, or weather
boarding. In designing the overcladding it
would be important that care be taken with
the detailing at junctions to openings,
parapet walls etc to ensure the water would
be excluded from the existing walling. It
might be possible to fix the overcladding to
the existing tiling and thus avoid the noise
and disruption in removing it.
Figure 9.7
Replacement of detached tiles in progress.
Spacers are in place; a vertical movement
joint can be seen above the little finger
Figure 9.6
The render coat bulging away from the
background (right), loss of adhesion
(centre) and cracking (left)
Tiles on a parapet had also become
detached. The top of the parapet wall was
constructed with a tiled concrete coping
bedded on to common brickwork with no
DPC, therefore any rain penetrating through
the coping tiles could allow repeated wetting
and drying of the brickwork and render
backing. The internal face of the parapet wall
was rendered. The horizontal tiles to the
coping had cracked at positions
corresponding to the joints in the concrete
