Any surface on the exterior of a building which is continuously exposed to the elements (e.g. wind, rain and temperature change) will weather over time, but there are certain factors which will determine how quickly this weathering will occur. Materials, orientation, location and contact with adjoining surfaces will all play their part. This blogs explores which aspects of a build are particularly vulnerable repeated saturation, under which circumstances weathering may be accelerated and what can be done to increase longevity.
Areas of Vulnerability
Near Ground Level
Any brickwork that close to surrounding ground and landscaping such as below the damp proof course (DPC) is more vulnerable to the repeated action of freeze thawing if saturated. This continuing cycle can cause damage such as spalling of the brick surface.
In additional to this, in saturated brickwork, active soluble salts contained within certain clay types and/or the surrounding material can cause a chemical reaction with the constituent of the Portland cement in the mortar. Also known as sulfate attack, this can cause the surface of the mortar joints to crack, the inside to crumble and expand, and the brickwork to be disrupted.
Bricks are not manufactured or tested for use as pavers.
Masonry such as cills, plinths, cappings and copings receive the brunt of more water during wind driven rainfall and therefore are more likely to become saturated. This is because they all feature horizontal or inclined surfaces and often project from the overall exterior brickwork. These structures may also increase the vulnerability of the brickwork beneath them as water cascades from them on to the surface below. Any decorative detailing which allows water to pool should be avoided.
For overhanging coping, bricks with a drip groove are preferred as this will help direct water away from the rest of the wall.
Location, Location, Location
Any brickwork in locations which are regularly exposed to severe weather conditions, such as wind driven rain, can be particularly vulnerable. In the UK areas are rated as sheltered, moderate, severe and very severe exposure to wind driven rain based on extensive metrological studies. All areas within 8km of the coast or river estuaries and buildings on high ground should be considered a grade higher than illustrated on the map.
As well as physical location, the height of any building should also be considered. The taller the structure, the more likely it will be exposed to a greater ferocity of elements such as wind and rain.
BS EN 771-1 states bricks must be declared into one of the categories below:
|F0|| Not frost resistant
|Should not be used in external applications|
|F1||Moderately frost resistant|| Durable in most building elevations except where saturation
and repeated freezing and thawing can occur i.e. below the DPC and projecting
|F2||Frost resistant|| Can be used in most normal building applications and degrees
of exposure. Check suitability of individual products with their manufacturer
Please note: The durability rating of a brick does not necessarily affect its appearance. Ask the supplier or manufacturer about specific brick durability ratings.
Engineering bricks are often specified for high degrees of exposure such as 150mm above and below ground in freestanding walls, however they are not sold for their appearance.
Facing bricks, which are mainly sold for their aesthetics (available in a wide range of types, colours and textures) may not be suitable for extreme situations, however it is worth noting that some Facing bricks do have engineering properties and may be more suited for projects in severely exposed detailing or regions.
Mortars and Joint Profiles
Mortar can be particularly vulnerable to weathering and deterioration. Usually a 1:1:6 mix of cement, lime and sand is sufficient for the majority of brickwork between the DPC and eaves. However, for the more vulnerable scenarios highlighted in this blog, a mortar of increased durability should be considered, but it should never exceed the strength of the bricks it is accompanying.
The mortar joint profile is also extremely important to the long term performance of brickwork. In these situations, the performance criteria is much more important than aesthetics with an emphasis on the importance of good workmanship.
The two joint profiles recommended for severe weather conditions are Curved (Bucket Handle) and Weather-struck as they both have excellent strength and weather resistance.
Dependent on the brick chosen bucket handle or weather-struck jointing should enhance the appearance of the brickwork whilst maintaining good resistance to the elements. Speak with an Ibstock Advisor for more information.
Further information regarding best practise with regards to vulnerable brickwork and mortar types, as well as guidance for other building challenges, can be found within the technical information section of the Ibstock Brick website or speak with one of Ibstock’s Technical or Design Advice Team.