How to repair cracked exterior cement rendering?

WombatRenno

I have an old 1910 cottage that is in pretty good nick but the cement rendering on one side of the house is a bit cracked & broken in some places. I've added a couple photos to highlight the condition, but it's clear some of the render has separated from the material inside the foundation as it has a hollow sound when tapped on. 

What is the best process for repairing the cracks and larger missing pieces? 

Should I pull away a whole section of the render that is hollow and use some sort of structural repair mortar to fix it?

I would like to complete a long-term repair that will maintain the render for the future.

For context:

• The previous owners (I assume was for some time) had the down-pipe draining directly into the corner between the render and the step, which I assume is why this area has seen the most significant degradation due to the consistent moisture exposure. I have now rerouted the down-pipe so this area is no longer exposed to as much moisture. 
• The area in the photos is ESE facing and gets most of the morning sun. It is otherwise out in the open (no roof etc.).
• The foundation is typical of a 1910 cottage - brick and wood (which you can see a bit of in the first photo). 

EricL

Hello @WombatRenno 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your exterior render.

It's difficult to tell what your renders current status is. Part of it might still be in good condition and is till well attached to the wall. My worry is that by removing parts of the render it will be necessary to remove the rest as it will compromise its structure. I can see sections of your render damaged by moisture and others by possible age. If you are not prepared to do a full render of the area, I suggest patching the cracks and small chipped sections with Earl's 1kg Concremate Expanding Cement. For larger sections, I recommend Davco 5kg 136 Rapid Patching Mortar. 

However, should you decide to explore what's behind the render, any damage that you discover will need to be addressed. This includes foundation issues, irrigation damage, moisture and condensation damage and anything else that you might find. But once all those issues have been addressed putting on a new render and painting the surface would be the best way to protect it.

Let me call on our experienced members @Dave-1, @Nailbag and @AlanM52 for their recommendations.

If you need further assistance, please let us know.  

Eric