What are the black marks on my Hemp Plaster

What are the black marks on my hemp plaster? 

Marks within and on the surface of hemp plaster are normally caused by moisture being trapped in the hemp fibres during the drying process. 

The drying time on hemp plaster can vary dramatically depending on the conditions, given the right conditions, it can take anything between four days and up to a month or more to completely dry depending upon the substrate, thickness of application, wetness of material and environmental conditions.

This should be monitored closely and action taken to adjust the conditions if there are drying issues. (Such as mould growth or black marks on the surface of the plaster) Gentle heat, plenty of ventilation and even dehumidifiers may be used cautiously in cold, damp buildings, during the drying process. 

Once the hemp plaster is dry, if the marks persist these can be, sprayed with a diluted bleach solution or Beecks Fungicide and gently wiped/washed away.