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Fibre reinforcement to plasters – problems associated with natural hair and alternative fibres, natural and synthetic.

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Fibre reinforcement to plasters – problems associated with natural hair and alternative fibres, natural and synthetic.

April 6, 17:00 - 18:00

Mortar analysis

Tom Balch, Rose of Jericho

Animal hair has been added to strengthen and reduce shrinkage in lime plasters for centuries. This reinforcement is particularly important when applying basecoat plaster to laths (especially ceiling laths) as it reinforces and strengthens the crucially important nibs from which the ceiling plaster ‘hangs’. The first ‘pricking-up’ coat traditionally contains hair reinforcement at a rate of at least 8kgs/m3 (c.4kgs/tonne). Subsequent coats to lathwork and all coats to solid backgrounds normally have hair added at the reduced rate of 5kgs/m3 (c.2.5kgs/tonne).

Hay and straw were sometimes used as alternatives, but the vast majority of traditional basecoat plasters were reinforced with animal body hair from horse, cow, pig or goat. When examining dry historic plaster it is normal to find hair reinforcement present and apparently in good condition. However, recent analytical work is suggesting that some degradation and loss of tensile strength can occur over time.

This degradation appears to occur more rapidly in currently available animal hair. The vast majority of animal hair is now imported in neat bundles from countries where anthrax is a problem, and the hair is cleaned and sterilised in the country of origin to ensure any bacteria spores are destroyed. This treatment, which can include boiling and/or steam treating, appears to decrease the resistance to degradation and reduce the durability of the hair in the alkali lime environment. It is thought the protective keratin proteins and natural oils in the animal hair are depleted during the sterilisation treatment.

Date: Wednesday 6 April

Time: 1700 – 1800

Price: £12 plus VAT (£14.40) or £130 plus VAT (£156) for the webicard which entitles you to attend the entire programme  from September to June at no additional cost (the webinars from September will be provided as recordings.

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