What Went Wrong? Porcelain Paving Installation Failures
This is the first in a series analysing landscape project failures as recorded by expert witnesses commissioned to produce court compliant statements for use by the court’s system.
All locations and company names have been redacted, and all images anonymised to avoid any conflict. All cases shown have been settled through proceedings.
Modus operandi – how the analyses are conducted;
In order to produce a series of inter-related articles, the same format will be used throughout.
All expert witness comments are made using either Industry Best Practice or British Standards where they apply when writing reports in the absence of any documentation or working practices mentioned as specification by a contractor.
PORCELAIN PAVING – British Standard BS7533;101 and 102. All comments are made using this standard.
Most common complaints and reasons for disputes and project failures.
- Lack or absence of bridge bonding slurry on the backs of slabs (or too little material applied)
- Lipping, or raised edges between slabs, causing trip hazards or unsightly shadows across the surface in artificial light.
- Mis-match between impermeable and permeable laying/grouting systems, using either permeable grout and impermeable laying base, or vice versa, allowing water to enter or become trapped under the slabs.
- Colour mis-match when two or more batches are used without ensuring colour matching and pattern/effect.
- Sharp joints, especially when laid with wide (10mm) joints in a grid or chequerboard pattern, corner to corner, leaving a dip in the grout in the four corners, causing injury to small toes, especially around swimming pool projects.
- Dry cutting blades used to resize slabs, leaving ragged sharp edges to the sawn side.
- Absence of cross falls and adequate drainage, allowing water to build up on the surface (surface tension) causing a slip hazard, especially during wet and frosty weather.
- Inadequate laying bed/base, using dot ‘n’ dab or incomplete beds containing voids.
The image below is a genuine example of a failed project, with comments describing the original complaint, and subsequent findings of the expert witness.
This is a side path leading from the front garden to the rear of a twenty-year old detached house. The original paving was lifted and removed offsite, and replaced with 20mm porcelain.
The total area paved was sixty square metres, all laid to the same specification.
The contractor used soft builder’s sand, which is not recommended due to its fine, rounded particles which do not compact properly, leading to instability. It retains water, causing poor drainage and allowing for movement. British Standard BS7533;101 calls for sharp sand.
The slabs were not fully slurried on the backs. Ensure a full layer – between 2mm and 3mm thick is applied to the whole of the back, enough to cover the pattern. This is the bridge bond between the laying bed and paving slab.
It would appear that the slab was laid using PVA (Polyvinyl Acetate) which is not waterproof and will break down in wet conditions or frost, leading to bond failure. The white residue is likely to be PVA (although no laboratory tests were deemed necessary) although it could be the release agent used to allow porcelain slabs to be removed from their moulds.
Polyvinyl Acetate – also known as white glue – is a water based polymer, used in schools for craftwork, or in carpentry to stick wood together.
All porcelain slabs should be washed, or brushed and cleaned with a damp cloth the remove the residue dust from the back of the slabs, otherwise the slurry bond may be compromised.
The use of PVA is not recommended in damp conditions, as an acid produced by cement and PVA together will break down any bond.
The grout was permeable, which allowed water to penetrate under the slab and accelerate the breakdown of the PVA.
This single photograph summaries many of the defects found when surveying paving projects.
The whole sixty square metres required lifting, the laying bed removed, and replaced using correct British Standard methods, paid for by the contractor by order of the court.
Over sixty percent of all disputes include paving, and over fifty percent of those concern porcelain projects.
