Filling floor cavity void to fit sliding doors

[a1topdog]

I'm having a set of external floor to ceiling glass sliding doors fitted, and the door fitters have advised that I need to fill the current (55mm) cavity void to level with the top of the floor brick work as the door frame needs to sit on a solid base. The frame will sit on the outside course of bricks but is not wide enough to also sit on the inner course, hence having to fill the void. The fitters have advised me to just back fill the void with concrete. Is this correct?

If so should I line the void with a dpm then concrete? Also what mix of concrete would you advise?

Thanks in advance.

 

[oldbutnotdead]

Hopefully they're better at fitting doors than advising on building work.
You need a cavity closer under the door, you also need them up the sides and a tray above the lintel with weep vents as well to prevent draughts, cold bridging and other nasties.

 

[a1topdog]

Thanks for the reply.

Their point is that the sill/ frame is not wide enough to sit on the inner and outer course of bricks. So if I did as you suggest and just fitted a cavity closure half of the frame at floor level would not be supported.

 

[oldbutnotdead]

In that case you need something structural above the cavity closer. Paving slab (not ideal, cold bridging), soldier course of bricks (ditto), nice wide timber plank (might rot and might compress over time causing movement problems).
Is the bottom of the door below dpc?

 

[a1topdog]

No, the frame will sit on top of the dpc.

 

[oldbutnotdead]

OK, that's not as bad then (their filling-in suggestion). What is the frame made of, how wide is it, how much of it will be sitting on the front skin & how much overhanging? And if the door is at DPC level where is internal floor level relative to the door? Is the floor solid or suspended timber?