Plinth/damp course -render fallen off

alexandramj

Hi there,
The render/concrete has fallen off parts of the plinth of my house extension. So I removed the rest myself- it crumbled off easily! The extension was done by the previous owners. 

I’m trying to fix this myself on a budget with no rendering experience.

Can I just paint the bricks with a masonry hydrophobic product, or must I render it with concrete? 

As you can see the pebble dash is also crumbling off but I can’t afford to get this redone professionally.
Can I just leave it as it is or is that risky for the breeze blocks underneath the scratch coat (which also rubs off easily)  p

I’ve had a few quotes but some ridiculous prices and varying answers so don’t know who to believe. 

Thank you!