In more detail; The plain card sub-roof is first covered with a thin white PVA glue and water mix. I then apply the white 'DAS' in small thin sheets, about the size of a Oreo biscuit. Once the roof is covered, I use a modelling tool to smooth out the whole shape and even add 'sausages' of 'DAS' to the sides and lower portions of the thatch. Once I am satisfied with the shape (this is done by eye after studying actual thatch roof shapes on the internet or historical books) I 'comb' the 'DAS' with a modelling tool, using a dragging action at first and then a prodding action when I am detailing the roof. The over-hang (the exposed section at the bottom of the thatch) is prodded with a cocktail stick in a jabbing motion. I then leave it to dry (or cook in the oven).
Once the main shape is finished and completely dry I add the topping or apex, the bit that covers the top of the roof. The rough shape is modelled with a 'sausage' of 'DAS', pressed in to the existing thatch, then 'combed' with a modelling tool and later trimmed back to the up-turned shape you see. The small indentations are meant to represent the way that thatch is held down by weaved straw or thatch.
You can also see some of the continuing problems I have with deformation following my mistake with 'cooked DAS'.
I am pleased with the finished thatch effect, which should really become apparent once the building is painted.