Over the last five years UK local authorities have paid out £35m on compensation and legal fees related to damp[1], leaks and damage. Given the funding challenge that local authorities face, they are under growing pressure to ensure that housing stock is fit for purpose. While some of the main causes of damp are well known, others are sometimes less evident. One example is plaster.
Here Tom Emery, Specifications Co-ordinator at Tarmac’s Limelite division, explains how a change of approach to plaster choice could help local authorities finally beat damp for good, and make significant cuts to annual maintenance bills in the process.
With over 1.6m local authority-owned properties across the UK[2], the sector provides a sizable proportion of the nation’s housing stock.
In urban areas, particularly in the Midlands and North of England, much of the council-owned housing is made up of 19th century solid-wall properties. For much of the latter half of the twentieth century, local authorities used traditional lime-based plasters throughout these properties, largely to great effect. However, due to the rise in popularity of gypsum plaster – and its perception as a one-size-fits-all ‘wonder product’ – it soon overtook lime-based products and became the plaster of choice in council housing. It has remained so to the present day.
There is no denying that price also came into the equation, with the accessibility of gypsum plasters freeing up precious costs from maintenance budgets which could either be used to undertake other remedial work, such as installing double glazing, or spent elsewhere.
However, one of the major product flaws of gypsum plaster is that it offers very poor levels of breathability, as it quickly absorbs and retains moisture from the surrounding atmosphere and substrate.
It is this distinct lack of breathability which makes gypsum plaster highly susceptible to damp and black mould growth. Crucially, the problem is often exacerbated by local authorities looking to make further cost savings, by attempting to cut energy wasted through heat loss. For example, the increased use of double glazing and cavity wall insulation will improve the air tightness of the property. However, a by-product of this is a notable increase in condensation, which in turn creates further damp problems due to gypsum plaster’s tendency to absorb moisture. What’s more, the removal of air bricks has also hampered the breathability of older properties.
Tom Emery, Specifications Co-ordinator
Treating damaged gypsum plaster is a lengthy and expensive process, with the plaster having to be removed, the walls treated with a Damp Proof Course (DPC) before waiting for it to dry – which usually happens at a rate of 25mm a month – to receive a backing plaster. Crucially, if gypsum plaster remains on the local authority’s specification programme for remedial works, and is used again once the old plaster has been removed, then there is no guarantee that the problems will not return.
Ultimately, this is where local authorities have both the opportunity and capacity to make a change; not just to their specification, but to the whole-life costs of their properties, and the living conditions of their tenants. Persisting with the use of gypsum plaster in aging housing stock will do little to reduce the prevalence of damp, and will only serve to add further cost – be it maintenance or compensation – into a section of the UK housing market which is already under immense strain.
The alternative is for local authorities to switch their plaster specification for older properties back to a lime-based product, such as a lightweight renovating plaster. Such products are able to mitigate the potential humidity and air-flow issues faced by ageing social housing properties, by allowing moisture to pass through them, dramatically reducing the likelihood of damp occurring.
One of the main reasons for lime-based plasters falling out of use was the application time, especially when compared to gypsum. However, modern variants are just as easy – and quick – to apply as their gypsum counterparts, and do not require the skill or expense of a specialist contractor. Crucially, renovating plasters also dry much faster than gypsum. In real terms, this translates to lower levels of inoccupancy due to maintenance work.
Typically renovating plasters, such as Limelite from Tarmac, include a salt inhibitor which increases the retention of dissolved solids within the plaster, helping to protect the decorated finish. The result is a highly breathable plaster solution which delivers balanced moisture movement through the construction fabric. In turn, this breathability allows the substrate to dry naturally and prevents damp and mould growth. What’s more, for walls with metal reinforcements, the fact that moisture isn’t retained within the plaster prevents any corrosion occurring.
While the balanced movement of moisture through the substrate in itself will play a huge role in preventing damp from occurring, it is also worth noting that the aseptic qualities of a lime-based product will further curb the spread of mould and bacteria. Given the negative health impact mould can have, the value of this further barrier to its growth should not be underestimated.
Ultimately, given that most local authorities are in charge of their own specification, making the change to a renovating plaster could make a sizeable impact on the amount of money spent on remedial damp problems, in particular those stemming from gypsum plaster. Not only is it an accessible way for councils to save money, but it can also promote a safer and more comfortable living environment for tenants. I would encourage those local authorities keen to make a change to their specification, to get in touch with suppliers who understand the challenges associated with this sector of the housing market and have an open and honest conversation about the most appropriate solution for their housing stock. Doing so will not only benefit the properties in question, but all the tenants who live there too.
For more information on renovating plasters, please visit www.limeliteplaster.co.uk
[1]http://www.bbc.co.uk/news/uk-england-leeds-38914352
[2]https://www.gov.uk/government/statistical-data-sets/live-tables-on-dwelling-stock-including-vacants – Table 100
