How to make a drip edge on a plastered fence post?

[sulfobus]

I have repaired fence posts with leca that have received red primer and plaster. The top stone is uneven old Öland stone. The old posts were frost damaged (were made with hollow bricks instead) and I suspect it was partly due to water running around the top stone as it does not have a drip edge. How would you prevent water from penetrating behind the plaster? The top stone is not yet mortared.

 

[Stuff]

Maybe ask a sheet metal worker to craft a hat in metal that is painted in a color that matches the fence?

 

[sinuslinus]

On page 55, there are a couple of conceptual solutions. http://vpp.sbuf.se/Public/Documents...983 Slutrapport Murat och putsat byggande.pdf

 

[hapazard]

Can't you just place a piece of tar paper under the stone, the transition between stone and paper should break the dripping.

 

[sulfobus]

Thank you for the suggestions, I was considering cutting a groove as a droppnäsa, but these suggestions are probably better.