Cracked floor under UPVC door

[Louis.]

Having removed the carpet by the front door I've found the floor cracked underneath the upvc door. I presume this has occurred when the door has been fitted and the bolts have been screwed down.

I have removed all the broken floor and want to repair this. The floor in the house is concrete with a bitumen top layer/DPM. What I have noticed is that by the front door it seems to just be concrete/sand and cement.

If I'm to replace this area can I just use sand and cement then a liquid DPM? I'm wanting to fit laminate in this room so floor needs to be flat.

 

[Wayners]

Looks like our estate buildings.

Builders (1960s) put a cavity on every door.
Guess it was easier vs doing properly. They put damp course roll over to bridge cavity and poured concrete over. Only 50mm deep then hollow cavity.
I removed. Lined cavity with dpm plastic and filled with concrete.
Both back and front do had cracks in floor and many local houses are the same so I pass on why.
Yours maybe the same

 

[Louis.]

I've highlighted the photo to make it easier to understand.

There's DPC exposed under either wall left and right (highlighted blue). Then a DPC wrapped over the door lintel (also blue).

Where the red line is where the bitumen layer starts and everything between lintel and red line is just concrete. There appears to be a void left and right of the lintel as a screwdriver just disappears into the abyss.

What's the best way to deal with this then? Shall I put another DPC down then lay screed over the top? It's all bone dry which is nice.

 

[Wayners]

Oh.

Asbestos tiles on the floor although they look like plastic. They probably are not plastic..
We popped all ours up in an hour and dumped some years ago however you may want to be careful and not dig at yours

 

[Louis.]

Oh.

Asbestos tiles on the floor although they look like plastic. They probably are not plastic..
We popped all ours up in an hour and dumped some years ago however you may want to be careful and not dig at yours

That's just a full bitumen layer over the concrete base, they aren't tiles.

 

[Wayners]

Bitumen was used to hold asbestos tiles at some point?
Anyway. Not what your asking.

If you knock with hammer you can hear that it maybe hollow if cavity runs under where your red and blue line is? Maybe.
Could line vertical edge with thin polystyrene against lintel/outside wall.
Stops the cold.
Dpm
Pour concrete mix.
Not saying I'm right but investigate.
Normal to have blocks or bricks under door.
Maybe you have drain pipe under there exiting house and lintel bridges over..

 

[Wayners]

Oh..

When they build houses/shops concrete floor can sink.
That's why shops have cracked tiles as floor base sinks but outside walls stay put.
This can cause cracks but not sure you have that problem as just doorway. Just thought I'd mention

 

[Louis.]

Bitumen was used to hold asbestos tiles at some point?
Anyway. Not what your asking.

If you knock with hammer you can hear that it maybe hollow if cavity runs under where your red and blue line is? Maybe.
Could line vertical edge with thin polystyrene against lintel/outside wall.
Stops the cold.
Dpm
Pour concrete mix.
Not saying I'm right but investigate.
Normal to have blocks or bricks under door.
Maybe you have drain pipe under there exiting house and lintel bridges over..

So if the bit between blue and red is hollow, shall I knock this out to then run the vertical insulation?

 

[Wayners]

Yes. I've done mine and a few others on our estate..

Didn't want to fill as is just incase it creates a damp bridge.

Investigate and have a think about it

 

[Louis.]

Removed the concrete and it seems this whole cavity has just been filled with rubbish. There's wood and nails in here.

Presume this isn't ideal as it will be bridging the cavity and potentially introducing damp?

Shall I remove all the rubbish from the cavity then do as above?

 

[Wayners]

Yes. Imo

 

[Louis.]

How much of the cavity do I need to clear?

I've gone down and found a DPC coming from under the base of the house. This isn't along the full length of the threshold cavity.

I've cleared this much so far, and feel I could be clearing forever? Shall I trim back that clear DPC flush then run fresh?

 

[Louis.]

I've shoved a tube onto the hoover and managed to clear loads more. It's about 30cm clear below the lintel DPC.

Is this sufficient?

 

[Louis.]

 

[Wayners]

Yeah that will do.
I'd drop some plastic in and fill with concrete mix.
Could use a rubble sack for dpm