Has anyone used false beams when putting placo on the ceiling… used to be able to get polystyrene ones, years ago… and whilst I would prefer wood… we may have to go the other route… needs to be lightweight and hollowish
The idea is to disguise where sheets of placo meet/fall short… on the new ceiling…of our little gîte…
All ideas welcome… 
Many years ago (going back 30 here) we had a building constructed in our garden as an office.
The ceiling was put up and rather than plaster it (the walls we breeze block which we just painted - it was an office - workspace after all) the builder nailed in flat batons to cover the gaps and the effect looked professional after the ceiling boards and the batons had been painted white.
Cheap and cheerful and very effective.
Just been helping a friend , I got him a roll of off cuts (side bits from the trunks) from the local serie . He trimmed, removed the bark, sanded and stained and they look like beams. He put them over some of the placo joints in their new kitchen , looks better than I expected. Saves a lot of filling.
I think that I would go down the cheapest way of buying some tasseau, or something similar, plane it, stain it and then glue it on. It doesnt need to look like massive beams, smaller is best in some instances !