Durability
The major factor of influencing the durability in Fyfestone
Architectural masonry is the degree at which it becomes saturated
with water. It may become saturated directly by rainfall,
indirectly by water moving upward from the foundations or laterally
from adjacent materials.
External Masonry
External masonry is much less likely to become saturated where
projecting features have been provided to shed run-off water clear
of the walling below.
Examples of such features are:
- Roof overhangs or copings.
- Throated sills.
- Bell mouths to rendering and similar features at the base of
tile hanging and other impermeable cladding.
Fyfestone Architectural masonry is inherently durable and if
used in accordance with the appropriate European Standard will last
the lifetime of the building into which they have been constructed.
They possess excellent frost resistance and, in general, provided
they are selected following the recommendations of BS 5628 : Part 3
then problems should not occur.
Durability is also governed by the characteristics of the units.
The compressive strength of the concrete blocks will determine the
units suitability, depending on the application and exposure
condition.
BS 5628–3 : 2005 gives general recommendations for the design,
construction and workmanship of masonry, including materials and
components and the main aspects of design, other than structural,
which is covered by BS 5628–1 and 2.
All Fyfestone Architectural masonry is suitable for conditions
near or below ground level. The inner leaf of external wall
constructions below d.p.c. where the cavity is filled is, together
with internal walls below d.p.c. considered protected and as such
any block can be used provided it meets the structural and
stability requirements of the building.
Frost action
Low temperatures alone do not damage masonry, but if it
saturated, or near saturated, the water can freeze to ice within
the fabric. As water changes from liquid to solid, it expands and
induces stress in the materials. Frost resistant materials should
be used in the design for masonry unless there are protective
features which protect it against severe wetting.
Extra care should be given to the choice of masonry units and
mortar if the masonry is liable to be splashed with deicing salts
from roadways or if the building is to be located in conditions of
extreme exposure weather.
Sulphate Resistance
Where the masonry remains wet and sulphates are present, the
selection of the unit needs further consideration.
However, aggregate concrete blocks have been used successfully
below ground level for many years, with a proportion used on sites
where sulphates are present and yet no failures have been reported.
Whilst blocks meeting the general requirements for use below d.p.c.
have been accepted as suitable for use in sulphate soil
classification DS1, work by the
Concrete Block Association, has shown that the 7N/mm² aggregate
concrete blocks tested were able to withstand conditions equivalent
to sulphate soil classification DS-3.
Carbonation is a major factor in achieving the necessary
durability and results from the open texture and permeability of
the aggregate block by allowing the surface to dry between the
manufacturing and backfilling operations.
DAMP PROOFCOURSE
The three basic requirements of dpc’s are their ability:
- a) to resist damp penetration from below
- b) to resist water penetration from above
- c) to resist horizontal damp penetration
The choice of dpc depends on a number of factors, i.e. exposure
and type of construction. Tables 1 and 1a detail the factors to be
taken into account.
| SITE EXPOSURE |
CONSTRUCTION RISK |
LOW RISE 1-3 STOREYS* |
MED RISE 4-7 STOREYS* |
HIGH RISE 8+ STOREYS* |
| Sheltered |
Low |
A |
A |
B |
| Moderate |
High |
B |
B |
C |
| Severe |
Low |
B |
B |
B |
| |
High |
B |
C |
C |
| |
Low |
B |
C |
C |
| |
High |
C |
D |
C |
*Building height and dpc standard
A dpcs specified with only basic normal installation
B dpcs carefully specified with detailing at vulnerable positions
and above normal site installation
C dpc’s very carefully specified and thorough detailing and high
standard of site installation required
D consideration to be given to change of basic type of construction
to that with a lower risk
It is beyond the scope of this manual to detail exact examples
of dpc’s and reference should be made to BS 5628: Part 3 :
2005.