Hi there,
I'm not well versed in these materials but from what I've picked up elsewhere, incorporating the right amount of fibrous material, such as
straw, in your clay dung mix can strengthen the wall/surface you're building. As for sticking to the building, using thin
chicken wire (think stucco) on the exterior before applying your mix
should help bind the material to the presswood and give it strength to hold together.
Definitely double check on these suggestions, as again I haven't worked with these materials, but when reading about
cob I picked these things up.