Adding damp proof course to French doors

ashe

We've got a guy in replacing a large window we had put in with a set of French doors 

the original window was a bodge job and we've never been happy with it, so looking forward to seeing the back of it. 

When he has taken the floor-level sill up, there is a gap between the floor and the external brick work. He has said the internal floor and external brick flat level has damp proof course but the gap and internal face of the bricks doesn't have one, but it's a fairly simple diy fix and I'm happy to have a go. 

He has suggested;

* 18 inch damp proof course roll along bottom of the gap and up the sides 
* fill this with concrete and allow to set
* snip off the parts that are proud of floor level
* carpet up to door 

just wanted to confirm this is correct course of action before I go ahead with it?

I'll add a photo to post #2 as just added one and it erased my post so had to type all out again 😂

ashe

It's the gap in this photo essentially that he is saying I'll need to line with DPC and fill with concrete 

ashe

If so presume I'll need;

https://www.screwfix.com/p/capital-valley-plastics-ltd-damp-proof-course-black-30m-x-450mm/59882

https://www.travisperkins.co.uk/ready-mixed-concrete-and-mortar/blue-circle-multi-purpose-ready-to-use-concrete-20kg/p/346658

& something to smooth/level it off with?

stuart45

How thick will the concrete be?

ashe

stuart45 said:

How thick will the concrete be?

Do you mean depth or thickness between the external brick layer and internal floor?

ashe

Just gone and measured it;

1.8m length
20cm depth
6cm width 

hopefully the 18inch DPC be ok as that's 45cm-ish?

stuart45

The thickness of the new concrete you will be laying over the threshold, as in  will it be 4 inches deep?

ashe

stuart45 said:

The thickness of the new concrete you will be laying over the threshold, as in  will it be 4 inches deep?

It's 20cm deep the hole, so 7.87 inches, and 6cm wide so 2.36 inches 

FreeBear

Did something similar with my front door - Had to remove a ruddy great lump of concrete which left me a ~50mm deep void to fill. Used an offcut of DPM to line the recess followed by a bucket of screed.

In your situation, I think I'd cut a few bricks up to fit in the bottom of the cavity with a thin(ish) layer of mortar on top. Whilst still wet. put a bit of DPM sheet in, then fill with concrete - Aim for a ~100mm thick layer tamped down & leveled off. If you try to fill the entire void with concrete, you are going to need around 50Kg. Using a few bricks to fill some of the gap, you can cut the concrete needed down to 20-25Kg.

stuart45

So you intend to leave the inner skin DPC in place and carpet over it?
Normal method is to remove one course of brick from the inner skin,, DPM over it and the cavity and concrete over it.

ashe

stuart45 said:

So you intend to leave the inner skin DPC in place and carpet over it?
Normal method is to remove one course of brick from the inner skin,, DPM over it and the cavity and concrete over it.

I'll have a look at what's there when he goes and report back, as he is nearly done. He said I could get rid of the inner skin dpc because it will have been originally where the wall was under the old window but that wall is gone now. I was thinking to just line the cavity with the 18 inch dpc and fill with concrete, but then @FreeBear above suggests this will need a lot of concrete so may follow his advice to raise the gap a little