Sand and cement renders have been the most common replastering method used on rising damp affected walls since the 1950s. Whilst effective, they can also present problems. Hudson Lambert of Safeguard Europe explains.
In the face of rising or penetrating damp, there is a need for internal plastering that is impervious to salt-based damp damage. Traditional strong sharp sand and cement mixes are effective at holding back damp and salts; yet they are slow and expensive to apply, and are associated with condensation risk, poor insulation qualities and a cold feel that is unpopular with building occupants. They are also not suitable for heritage structures because they are inflexible, don’t breathe and can damage underlying brickwork.
For this reason, Safeguard has developed two new replastering systems that combine the effectiveness of sand and cement without the drawbacks. Both Dryzone Renovation Plasters and Dryzone Express Replastering complete the Dryzone System range of rising damp renovation products, enabling the sourcing of all necessary materials from one place.
The Dryzone System enables the treatment of rising damp from start to finish. Simply install a new damp-proof course with either Dryrod DPC Rods or Dryzone DPC Cream and choose one of the plastering specifications below.
Replastering System No.1: Dryzone Renovation Plasters
Dryzone Damp-Resistant Plaster is a modern formulation of breathable damp and salt resistant plaster that can be applied with traditional plastering techniques. For older buildings, Dryzone Hi-Lime Renovation Plaster is also available.
Unlike sand and cement renders, Dryzone Renovation Plasters are non-destructive to the underlying masonry, do not require gauging and provide a warmer surface. Simply mix and apply two coats.
These highly effective Safeguard renovation plasters can be applied to walls while they are still damp and has a porous structure which controls salt migration, allows walls to dry out by evaporation and results in higher thermal resistance, reducing the risk of condensation. Other properties include a low compressive strength ensuring that the plaster can easily be removed at a later date without damaging underlying brickwork; high water vapour diffusion and conformity for the EN998-1 CE Standard as ‘Renovation Mortars’.
Dryzone Damp-Resistant Plaster is applied in two layers as a 5mm anchoring rough coat and a 15mm to 20mm top coat. The working time of the plaster is 30 – 60 minutes depending on temperature and humidity; and a 2mm skim coat can be applied after 24 hours.
Replastering System No. 2: Dryzone Express Replastering System
This specification utilises plasterboard and provides the speed and convenience advantages of a traditional dot and dab plasterboard application and also provides a salt and damp-proof interior wall surface.
The system is quicker and consequently less expensive to install per m2 than traditional ‘wet’ plaster systems. These materials combined allow for treatment and room reinstatement in around a day – a massive improvement over the weeks that more traditional methods may take – and obviate, for example, problems associated with decanting tenants for significant periods of time.
There are two elements to the system: Dryshield Cream, which primes walls; and Drygrip Adhesive to direct bond plasterboard to treated walls. Armed with these products, a skilled operative can treat rising damp, replaster and complete re-decoration in just 24 hours.
Once a DPC is installed, Dryshield Cream is applied to affected walls. It is a breathable, salt-resistant water-repellent that weakens the crystal strength of salts forming in or at the masonry surface as damp evaporates. Easy to apply by brush or roller, the cream not only acts as a primer for Drygrip Adhesive but also penetrates the masonry structure deeply so as to form a durable, robust bond.
Developed for ‘dab’ fixing plasterboard directly to masonry surfaces, Drygrip Adhesive forms a strong and long-lasting bond and is resistant to both salts and damp. Once fixed, the boards can be tape-jointed and skimmed as in ordinary drylining situations.