The Brick Development Association offers some advice on ensuring the longevity of brickwork
In order to enhance durability, it is important when selecting and working with brick to consider its properties. Events that can diminish the lifetime of brick include deterioration by saturation and frost and ways to prevent these threats to brick will be explored in detail here.
Firstly, to the issue of saturation. Bricks which become waterlogged may freeze in winter and this conversion of liquid to solid increases the brick’s volume by 9 per cent.
For some types of brick, freezing and thawing repeatedly is detrimental to their quality. Additionally, when a brick is saturated for a long length of time, it becomes prone to sulphate attacks, unless it is protected by suitable mortar.
Another issue brick users should be aware of is exposure to harsh weather conditions. This can vary across the country, and driving rain can be more of an issue if a project is located in the southwest of England, or on west coastal areas of Scotland and Wales.
It is also advisable to bear in mind that different walls on the same building may be subject to different levels of exposure, and treated accordingly. Further recommendations on these issues can be found in the Brick Development Association’s (BDA) guide to Severely Exposed Brick, which can be downloaded from their website www.brick.org.uk.
How can these issues be prevented, in order to maximise durability and keep clients happy with the aesthetics and quality of your brickwork for years to come? One reliable and aesthetically pleasing way to reduce brick saturation is to introduce design features that shed run-off water clear of the walling below.
Roof overhangs or copings, projecting and throated sills at openings, bellmouths to renderings and similar features at the bottom of tile hanging and other claddings can provide protection to wall heads. Damp-proof courses (DPCs), flashings and weatherings can also protect brick from saturation.
The best way to lengthen the life of bricks, and take a proactive stance before the problem arises, is to choose a brick which is frost-resistant.
BS EN 771-1 classifies bricks into three categories: F2 for severe exposure, F1 for moderate exposure and F0 for passive exposure. If a project entails that bricks will be subject to repeated freezing and thawing, bricks from the F2 category should be used in the project.
F1 describes bricks which are generally durable except in a saturated condition. They are not as durable as F2 bricks, but generally suitable for use on the external face of a building, so long as measures to prevent saturation have also been undertaken, such as using projecting eaves and damp proof courses.
Bricks classified as F0 are prone to damage by freezing and thawing, and so should only be used inside buildings, or behind impervious cladding. If bricks in this category are being used in a project constructed in the winter, they should be protected if left on site overnight.
Another important way you can prolong the life of brick on a project is through using the correct mortar, as some mixes are more prone to saturation than others.
Mortars can be mixed with the aim of matching the durability level of the bricks. To enhance durability, simply increase the cement content. In general, designation iii of BS5628 mortars, M4, are likely to offer the best overall balance of properties for external walling in the UK.
However, this is not applicable to bricks used in severe exposure conditions, where designation (ii) M6 or even (i) M12 mortars might be better suited to clay brickwork. For a project-specific recommendation, it is best to seek the advice of the brick manufacturer.
The BDA recommends that mortar is measured using a gauge box or bucket and not a shovel, as cement is a free-flowing dry powder which occupies a smaller volume, so mixing using a shovel will result in a leaner combination than intended.
On site, carefully protecting the materials that are utilised can increase the durability of the brick by years. Bricks should be stored on a prepared hardstanding, and covered with well-secured polythene sheeting or tarpaulins, and cement and lime should also be under cover during the night.
To summarise, brickwork quality can easily be maintained if the right bricks are selected for the environment, the mortar is mixed correctly and the bricks are stored in the right way. It is also worth considering preventative design measures to prevent saturation.