If you're familiar with the process of laying electrical conduits and water pipes under floors (known as "carcassing") you'll know that they are laid on top of the concrete floor base ("betao de massame") and are then covered by a thin screed ("betonilha"), normally of cement.
The inclusion of 'jorra' (pitch or bitumen) suggests that the screed is made of bitumen (like a tarmac pavement) or is a reference to the practice of laying a thick layer of bitumen between the concrete base and the screed as dampproofing - probably the former. You will find references to 'bitumen screed' in Google.

I'm drawing on my experience both of translating this type of construction text and of actually carcassing and laying screeds in my younger days!