Cob: linseed oil

[Matthew HALL(SED)]

I recently refered to the use of linseed oil as a natural surface treatment for earth walls and
renders. Linseed Oil is obtained from linseed which grows on the flax plant and can be obtained by
various methods. The oil is refined to remove certain naturally-occuring undesirable chemicals and
sometimes further treatments are used such as earth bleaching (to give very light drying oils). The
natural odour of Linseed oil can also removed through a deodorization process. 

There are 2 types of linseed oil available; raw and boiled. Raw Linseed Oil is just that,
completely untreated prior to packaging and contains no additives. Boiled linseed oil has been
altered through the addition of chemical drying accelerators, such as certain solvents and drying
agents. Boiled linseed oil is frequently mixed with 10-15% stand oil which is a drying oil of
increased viscosity, which is achieved through heating the oil in the absence of oxygen. The word
'solvent', in this context, is often wrongly associated with being ecologically harmful but many
common, natural materials are solvents and are very much needed for everyday life such as water,
alcohol:) 

In short, raw linseed oil is the pure extract from natural plant seed and takes longer to dry than
boiled linseed oil which includes drying agents but that aren't necesserally non-organic or
harmful. 

Regards
Matthew



____________________________________________________________________
Matthew Hall BSc (Hons) GradBEng
PhD Research Student
Centre for the Built Environment
Unit 9 Science Park
Sheffield Hallam University
Pond Street
Sheffield S1 1WB
England

Tel: +44 (0) 114 225 3200
Fax: +44 (0) 114 225 3206
E-mail: M.Hall at shu.ac.uk