Taking stock of social housing plaster pains

// the building envelope

Social housing is a valuable component of UK housing stock. However, due to lack of funding compared with the private sector, cost is often a key purchasing trigger when specifying building materials. Plaster is one of the most extensively used materials, yet compromising quality to reduce cost can lead to long-term property maintenance issues. Here, Iain Spence, Technical Manager for Tarmac’s Limelite range, puts forward the case for alternative plaster use in social housing.

With the UK’s population density rising, along with the number of tenants living in social housing, there is a great strain on the building fabric of many social housing properties. Combined with a lack of affordable housing stock and new-builds, tenants are living in properties which were never built for the purpose nor occupancy level which they are currently being used for.

The initial specification process is different for public and private sector housing. With housing association properties, building materials are usually specified by the housing association or a procurement framework, rather than the contractor. In the case of plaster, if any remedial work needs to be undertaken, the plasterer will often find that materials have already been selected for them.

Housing association properties are typically supplied with gypsum plaster, due to the ease of application and low cost price, but it possesses some inherent weaknesses which bring into question its suitability.

Moisture mismatch

A key issue linked to gypsum plaster is its difficulty in handling moisture.  The hygroscopic nature of gypsum means it easily absorbs and retains moisture from the surrounding atmosphere and substrate. Damp then leaves the plaster susceptible to the growth of black mould and salts.
The bulk of UK social housing stock is relatively old, and damp is a regular issue. Double glazing has been used to improve the quality of social housing stock, but while it may improve heat retention and offer better sound insulation, it can diminish ventilation and increase humidity levels, highlighting the limitations of gypsum plaster.

Remedying the effects of damp on gypsum plaster often involves the difficult process of removing the original plaster, and treating the walls 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; all at the expense of the housing association. This can be a time-consuming process and there is no guarantee of a successful outcome.

Re-education of plaster choice

Lightweight renovating plasters, such as Limelite from Tarmac, have proven to be highly successful for period properties, and many housing association properties could feasibly fall into this category, given their age and susceptibility to damp.

An important benefit of a lightweight renovating plaster is its ability to mitigate the potential humidity and air-flow issues faced by ageing social housing properties, by allowing moisture to pass through it, which dramatically reduces the likelihood of damp occurring. Typically, it includes a salt inhibitor which increases the retention of dissolved solids within the plaster, helping to protect the decorated finish.  The result is the balanced moisture movement through the construction fabric which allows the substrate to dry naturally.

The installation process is relatively similar to the traditional method: first the damaged plaster must be removed and then, if needed, treated with a DPC. The wall can then immediately be plastered with the lightweight renovating plaster and coated with high-impact finishing plaster before being painted with a water-based emulsion.

One final benefit of renovating plaster is that you do not have to wait for the walls to dry before plastering. The typical drying time for renovating backing plaster is just one day, whereas gypsum-based backing plasters can take up to 10 days or even months to dry during the winter; further drawing out the repair process and finances.

Final thoughts

In short, I would urge housing associations currently specifying gypsum-based plaster to re-think the reasons behind this choice. While budgets are often tight, the potential remedial work would go far beyond the slightly higher material costs of a lightweight renovating plaster. The poor moisture handling ability of gypsum based plaster is a key trigger for damp, and the only way to truly tackle the issue is to reconsider its use during the specification process.

For more information on renovating plasters, please visit www.pozament.co.uk/product-family/limelite.

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