That's why a protective coat must be applied. This coat consists of size of 70 gr. To make size you let the lime grains soak one night in cold water. The size is applied to the linen with a wide brush. When the first coat is quite dry, it is brushed lightly.
Powdered chalk is added to the size.
This mixture is applied on the first coat. When the second coat is quite dry, brush it lightly again. Add chalk to size that only contains 40 gr. of lime per liter. Add at least 2 liters of chalk to 1 liter of size. Thus you obtain a pulp that is just liquid enough to be applied easily and yet gives a few millimeters of coating.