Making good line drain

I bought my house last year and one issue i could see immediately was that the back patio which runs the length of the house was slightly above the interior floor level!

The house is a mixture of solid stone and un-insulated cavity walls.

Although there was only minor damp issues I still wanted to improve it so I have installed installed a line drain along the length of the house.
Unfortunately, due to the drainage outlets I had to install it nearly level with the DPC to allow a suitable fall. Although not ideal my building inspector (I have recently finished an extension on the other side of the house) said that I could only do so much and that it was an improvement anyway.

Could anyone recommend how I fill the void behind the line drain where the back of the line drain meets the wall? The void varies from 1-15mm. I wasn't sure if I could use builders silicone instead of cement as its quite small in places.
I intent to repaint the plinth with a good quality exterior paint.

Thanks in advance

 

it's too small for stones, but if you put grit in, it cannot crack and will not cause damage to wall or drain with seasonal movement. Keep some by for topping up when it settles (easiest when fully dry)

The preference for stones is that the bigger the particle, the less it supports water movement by capillarity, and the better it drains. Cobbles or pebbles are best of all.

 

Keep it as a void. Use a polymer or polysulpide mastic if you plan to paint it, not silicone.