The soda solution is made by boiling 1 litre of water with 50 g of soda powder. The liquid is applied when still warm. Potash solution is either based on pure potassium carbonate or on wood ashes, which contain about 96% potassium carbonate. A potash solution is made up by boiling 1 litre of water with 0.5 litres of pine ash and letting it simmer for 15 minutes. The solution is sieved and applied while still warm. The treatment has to be repeated every two to three years.
Soda and potash lye have been used for surface treatment in many Swiss villages for hundreds of years, and the buildings have kept well. A drier climate is, of course, partly responsiblefor their success.
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