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Heritage and listed buildings require due care and attention when specifying paint and protective coatings. This is due to the traditional construction techniques and the building materials such as lime based renders natural stone and even cob. Another modern feature often negated from heritage buildings is a damp course. When a modern film forming paint is applied to the fabric of a heritage structure without a modern damp course, moisture becomes trapped in the substrate leading to issues with damp. The knock on effect of this damp is the formation of mould which is a health hazard.

Also, the building structure itself can become damaged due to the build-up of trapped moisture content.

Promain have an extensive range of coatings for heritage properties. This range includes highly breathable mineral silicate paints from manufacturers Keim & Mapei. And traditionally formulated internal and external lime washes and linseed oil paints from the Traditional Paint Company.

Heritage Coatings

Historical church buildings tend to be constructed from natural stone and lime mortars/render. They are also generally without a damp course or central heating. Buildings constructed in is this fashion create atmospheres of high humidity. This is caused by the moisture leaving the substrate in the form of a water vapour. This then leads to formation and spared of mould within the building. This moisture can also cause water stains.

When specifying a coating for the refurbishment of historic church buildings it is of high importance the specified coating has a good level of breathability, stain blocking and anti-fungal properties. Our technical team would specify a performance coating such as Classidur Tradition. Classidur Tradition is specifically used for historic buildings, including churches. Classidur Tradition has excellent stain blocking properties and a very high resistance to the growth of mould.

Most heritage and historic buildings are coated externally with lime based renders. Lime based renders are also being applied to modern buildings in recent times. Lime based render are by far the most breathable of all render types. They are also relatively soft in comparison with modern sand and cement renders. This makes lime based renders particular suited to historic timber frame building. As the flexibility allows the render expand and contract with the buildings natural ebb and flow. Any type of paint coating applied to lime render will need to be highly breathable to allow the moisture to escape from the substrate and avoid damp related issues cause by trapped moisture. The coating will also need to be able to expand and contract with the building natural movement.

Lime washes such as The Traditional Paint Company Exterior Limewash can provide these required properties. Lime wash chemically bonds to the surface by preforming a chemical reaction and provide a high level of micro porosity. Lime washes however need to applied in the traditional way, by wetting down the walls and applying the wash sparingly. Applying to thick will result in unsightly mud cracking. Another alternative would be to apply a mineral paint such as Mapei Silexcolor. Mapei Silexcolor is based on a silicate base these type of paints also chemically bond to the surface and have an extremely high level of breathability. Another advantage of silicate based mineral coatings is the paints longevity, requiring less frequent routine maintenance than modern paints.

As with external substrates on historic buildings, internal substrates also tend be constructed from lime based renders and in some cases cob wattle and weave. It is of high importance a breathable and flexible paint is specified for the coating of internal walls constructed from these types of traditional materials. Application of a highly breathable coating will allow the moisture content within the substrate to escape through the breathable coating in the form of a water vapour. Allowing the trapped moisture will negate issues caused by damp.

Applying a modern form filming paint will hinder the passage of the vapour, leading to moisture entrapment and damp issues. An excellent paint to specify for this type of application is Keim Optil. Keim Optil is a silicate mineral emulsion formulated for interior use. It can be applied on to lime based renders and previous painted surfaces. This coating is highly vapour permeable, allowing the free passage of water vapour trapped in the substrate. It can also be applied to walls subjected to efflorescence. Keim Optil will hinder the formation of mould and fungi, so it particularly suited to historic buildings constructed without a damp course. Another benefit of Keim Optil is its light enhancing properties which can help to remedy difficult lighting conditions.