3D printed parts are stronger in the X and Z direction than the Z direction. It has struck me that there may be a simple way to improve layer adhesion.
After printing, say, the fifth layer of a model, the nozzle should make another circuit just inside the inner skin, but, instead of printing a continuous length of plastic it should stop every 5 mm or so and extrude sufficient plastic that could run down the inside of the wall to a depth of 5 layers or so. In this way there would be strands of plastic running in the Z direction as well as X and Y. During this circuit it may be better to have the fan switched off.
At the sixth and subsequent layers this process should be repeated, but offset slightly at each layer.
A further improvement may be if the infill was arranged so that there were little channels for the plastic to flow down. In the attached picture. for instance, there is a small channel which could guide the molten plastic.
