pouring a step

[ted]

I have to pour a concrete step to a pvc door with built in horizontal door seal. It's about 900mm wide about 50mm high and I guess supports the door seal underneath and prevents water falling in to the cavity. It just projects 20mm from the door seal outwards.

What mix of concrete should I use and how would I pour it to avoid cement falling down into the cavity? Any tips appreciated.

 

[dble8]

you can get readymix bags just add water type for that amount, get one bag should do it.just be careful and it wont go in the cavity or cover it with anything that works so the concrete wont go down that way