My balcony in the apartment seems to have a crack in the render. I am wondering what could cause this and how to fix it. I have timber decking on the ground and I’m not sure if that is causing the issue ( is there water pooling underneath it and causing rising damp - the decking has been there 17 years by the previous owners). It is only happening on the edge.
As you've mentioned, the cracking could be caused by several reasons or a combination of those. Movement, moisture or even just aged render could be the issue. Even after investigating and removing the delaminated render on that corner, I'd suggest that you might never discover the actual reason for it. If the decking has been there for a long time and the cracking has only begun recently, it doesn't sound like they're necessarily associated. You might find that they never installed an external corner trim. Corners are prone to cracking, and these trims give the render something to bind into. If there is no trim, you might consider installing one.
I'd recommend you use a flathead screwdriver to pick out all the damaged render on the corner until you reach solid material. You can then patch the area with Dunlop 4L Premix Render Joint And Patch. Here's a handy step-by-step guide: How to render. After you've applied the render, take a coarse bristle brush and stipple the area to mimic the effect of the surrounding render. Make sure also to cover your decking so you don't get cement residue on it.