Read up on Safeguard Europe's expert advice on penetrating damp

Hudson Lambert, Director of Safeguard Europe, considers the issue of penetrating damp in new and converted properties, and how modern masonry treatments can solve the problem.



ater ingress into masonry is an age-old problem. Many building stones are naturally porous, and the external walls of many older properties – residential or non-residential – encountered in conversion will be constructed with bricks that are considerably more porous than would be permitted today. Walls constructed from porous materials soak up water every time it rains – often acting as a conduit for rainwater to permeate through to the inner face of the wall where it presents itself as damp patches or blistering paintwork.

They are also less thermally resistant than dry walls, which means that heat loss from the affected building is increased. Test work carried out by the University of Portsmouth showed that a modern brick lost half its insulation value when fully saturated with water, and a study by English Heritage has shown that the loss of insulation value can be even higher for more porous historic bricks – as would be the case using salvaged/reclaimed in new buildings.

Of course, not all rain penetration through masonry is caused by the porosity of materials; defects such as cracks, faulty pointing and poorly sealed doors and windows are a primary cause of many penetration problems. However, where masonry is particularly porous, it can be a major contributing factor, and for this reason, there have been efforts over many years to develop products that can be used to reduce the permeability of such masonry.

In new properties, defects are typically a function of craftsmanship issues, such as poor detailing and, for instance, poorly installed or designed proprietary dry verge systems that shed water onto gable-end walls rather than taking it to the eaves (this can be identified by heavy streaking down brickwork).

Remedial measures can be taken to waterproof porous brick in conversions and renovated properties, and to protect new brickwork with pre-emptive treatment; by way of applying colourless masonry water-repellents that have been designed to reduce the permeability of masonry without affecting its appearance.

Early attempts to achieve this kind of protection involved liquids made by dissolving waxes or linseed oil in a solvent. These were simply painted or sprayed onto masonry and could block rain penetration for a time. However, they were vulnerable to discolouration and could often become sticky and attract dirt. Their main disadvantage was that they worked by blocking pores of masonry, trapping moisture in walls and preventing it from evaporating.

These days, the most effective masonry water-repellents are based on silicones. The main reasons for this are that modern silicone water-repellents form an incredibly long and lasting bond with most types of masonry and that they line the pores of masonry rather than blocking them – allowing the masonry to ‘breathe’.

The first silicone water-repellents were simple solutions of silicone resins in carrier solvents such as white spirit. Once applied, these formed a resin coating on the masonry surface and suffered from the same drawbacks as other resin solutions such as linseed oil-based products – i.e. they blocked the pores of the masonry and trapped moisture.

The 1970s saw the introduction of water-repellents based on specialised silicones. These were still solvent-based, but the molecules were smaller than silicone resin molecules, allowing them to penetrate below the surface of the masonry. Their water-repellent effect was partially derived from lining the pores of the masonry, rather than blocking them, which meant that treated masonry retained a degree of breathability. Further developments in the 1980s saw the introduction of another class of silicones known as alkoxysilanes. These had an even smaller molecular size which allowed deeper penetration into masonry and improved breathability.

These developments meant that by the mid-1980s solvent-based silane/siloxane water-repellents were available that combined excellent water-repellency with high levels of breathability (<10% reduction in water vapour permeability). The best products had long life-spans (often more than 10 years) compared with cheaper products based on metal stearates which typically broke down the effects of UV radiation from the sun within two to four years. However, penetration depths were limited to a few millimetres which limited their performance as even the smallest surface crack could allow wind-driven rain to pass behind the treated layer.

In terms of performance, the solvent-based silane/siloxane water-repellents were not improved upon until the introduction of masonry water-repellent creams, such as Stormdry, in the 2000s. These also utilised silanes and siloxanes as their active ingredients but formulated into a high-build cream that allowed deeper penetration into the masonry (>10mm in Fletton bricks for the best formulations). Masonry water-repellent creams appear white when applied to masonry, but become colourless once the cream has penetrated.

The proportion of active ingredients as well as the blend of silanes and siloxanes varies considerably between different cream formulations so it is difficult to make generalisations. However, the high penetration depth of good quality masonry water-repellent creams provides longer life expectancy – largely since any molecules of active ingredient more than 2mm beneath the surface of the masonry cannot be attacked by ultraviolet light. In the case of Stormdry, accelerated ageing tests carried out by independent laboratories suggest a life expectancy more than 25 years.

A further benefit of cream formulations is that they are much easier to apply around details such as doors and windows than liquid products which tend to be applied by spray.

The durability of silicone water-repellents is largely due to the strong covalent bond that they form with the silicon atoms present in most masonry materials including brick, mortar and sandstone. However, certain masonry materials such as pure limestones do not contain these silicon atoms and, consequently, the performance of silicone-based water-repellents is reduced on these substrates. These substrates can be treated through specialist techniques and product selection, but it is advisable to seek technical advice from the product manufacturer before doing so.

Safeguard Europe’s range of market-leading, proven damp-proofing solutions is supported by the company’s own highly qualified and experienced staff. The support and know-how it offers is extended to contractors, specifiers and property owners and includes technical advice, specification help, research and even in-house laboratory analysis of plaster and masonry.

A new CPD seminar created by Safeguard Europe offers an in-the-workplace CPD called ‘Dealing with Penetrating Damp’ which sets out four steps to help architects, builders and other building professionals to deal with both the causes of penetrating damp and the factors which can exacerbate the problem.

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