Get plastered, without the damp patches

A change in plaster choice can help landlords and local authorities to eradicate damp and cut their maintenance bills in the process, argues Tom Emery of Tarmac

Over the last five years, UK local authorities have paid out £35m on compensation and legal fees related to damp, leaks and related damage. Given the funding challenge that local authorities face, there’s a growing pressure for them to ensure that their housing stock is fit for purpose. While some of the main causes of damp are well known, others are sometimes less evident. Plaster is one example.

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 20th century, local authorities used traditional lime-based plasters throughout these properties, largely to great effect. However, gypsum plaster’s rise in popularity – and the general perception that it’s a one-size-fits-all ‘wonder product’ – meant it soon overtook lime-based products and became the plaster of choice in council housing up to the present day.

Impact on building fabric

There is no denying that price also comes into the equation, with the accessibility of gypsum plasters freeing up precious costs from maintenance budgets. However, one of the major 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.

Its distinct lack of breathability makes gypsum plaster highly susceptible to damp and mould growth. The problem is often exacerbated when local authorities carry out further energy efficiency upgrades, for example by fitting double glazing and cavity wall insulation. While these methods improve air tightness, they also lead to a notable increase in condensation, which combined with gypsum plaster’s tendency to absorb moisture can create further damp problems .

Treating damaged gypsum plaster is a lengthy and expensive process, involving plaster removal and wall treatment with a Damp Proof Course before waiting for it to dry, typically at a rate of 25 mm per month, to receive a backing plaster. Crucially, if gypsum plaster remains on the local authority’s specification programme and is used to replace old plaster, there is no guarantee that the damp problems would not return.

The case for renovating plasters

Ultimately, 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 would do little to reduce the prevalence of damp, and will only serve to add further cost into a section of the UK housing market 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 airflow issues by allowing moisture to pass through.

One of the main reasons for lime-based plasters falling out of use was their longer application time, especially when compared to gypsum. However, modern variants are easy and quick to apply 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 means the properties don’t have to stay unoccupied due to maintenance work.

Typically, renovating plasters include a salt inhibitor that 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 building fabric. This allows the substrate to dry naturally and prevents damp and mould growth, and prevents corrosion in walls with metal reinforcements.

In addition, the aseptic qualities of a lime-based product will further curb the spread of mould and bacteria. Given that most local authorities are in charge of their own specification, switching to renovating plaster could make a sizeable impact on the amount of money spent on remedial damp problems, in particular those stemming from gypsum plaster. In addition to being a budget-savvy alternative, it also promotes a safer living environment for tenants.

Tom Emery is specifications coordinator at Tarmac’s Limelite division