What Went Wrong? Patio Edging Detailing Failures
This article is the ninth in a series of articles written under the heading of ‘What Went Wrong?’ involving landscape projects that have failed for one reason or another. All cases are genuine court claims, examined using notes taken from expert witness reports commissioned to produce court compliant statements for use in a claims court.
Locations are anonymised to prevent conflict. All cases have been settled through court claims, or by insurance companies.
Using the same methodology throughout the series, to ensure the same standard of information is followed, with an introduction to the claim, the problems identified, and the outcome of the case.
All expert witness comments are made using either Industry Best Practice, or British Standards where applicable, in the absence of any specification provided by the contractor.
PATIO EDGING – SMALL UNIT INSTALLATION. All matters of design and installation of paving are covered by BS7533:101 and 102. As the British Standards are only advisory, on every occasion, the Consumer Rights Act 2015 will apply to claims of poor workmanship.
The most common complaints involve separation and movement of small element paving units breaking away from the main body of paving.
Many designers and specifiers produce schemes with an outer perimeter edge of small element paving – either a sett version of the main paving used in the scheme e.g. tumbled sandstone setts used in conjunction with standard sized/random rectangular patterns as a design detail for aesthetic purposes, or, more frequently in court claims, concrete block paving units.
Inboard detailing – rows of blocks or setts laid against the building or drainage channels – are rarely subject to failure, as they are held captive between the main body of paving and the rigid building/drain.
External Edging Sett/Block Installations
The photograph shows a typical edge against a lawn, separating a porcelain patio from the grass. The only reason for such a design decision could be aesthetic, with two different colours creating a more interesting terminal to the project.
1. Laid at the same level as the lawn, with no change of level, there was no obvious practical reason for the additional paving.
2. The blocks were laid as a double row of half-bond units, over soft builders sand and cement with no oversailing foundations from the underside of the main paving works.
3. There was no bridge bond slurry connecting the setts to the sand/cement, nor any indication of any jointing material between the blocks.
4. Within a short period of time, the blocks have migrated away from the paving, there being no mortar haunching to secure them.
5. In effect, the concrete blocks had been added to the main paving as a separate entity.
6. This type of ‘additional installation’ is always bound to fail, as there is no inherent strength of integrity to the construction.
Securing Edging Blocks/Setts to Paving Slabs
The cross-sectional drawing shows a typical constructional make-up of a porcelain paving project, including;
a. Soil and ground sub-base.
b. MOT Type 1 base.
c. 30mm sharp sand/cement mortar laying bed.
d. 20mm paving slab
e. Reinforcing mesh sheet within the mortar bed, extruding from the main paving.
f. Concrete foundation under the sett edging, with the mesh under the sett.
NOTE; The sett is 75mm thick, whilst the porcelain paving is only 20mm thick.
By use of this simple technique, the edging sett/block becomes an integral part of the paving structure, and is not an ‘add-on’ feature.
Other Issues with Edge Detailing
If the same materials are used – sandstone setts for example – there should be no problems with the mix of sizes and their surface treatment vis jointing or pointing, as the same compound can be used across the site.
The use of concrete blocks is more problematic, as the units are not intended to be pointed, but butt jointed and finished with kiln dried sand, which is not compatible with standard paving pointing materials such as resin-based products.
When pointing the main body of work, any jointing material residue that comes into contact with the concrete blocks can cause staining to the surface.
This often leads to issues where the blocks are open to water ingress, which can cause problems with freeze thaw damage, even when they are laid using a bridge bond slurry.
Summary
This particular project was condemned across the board, as there were so many other problems on site, including breaching damp-proof course, no bridge bond slurry on any of the slabs, with every unit loose within its (soft sand/cement) laying bed, with trip hazards across the patio.
