Advice on the repair of the concrete floor - deep large hole in the floor

[Danny Hardy]

Hi, thanks in advance for any advice.

When we had a new front door installed, we also removed a low wall that previously sat beneath a window. This has left a hole in the floor, which is part of the cavity wall. I now need to fill this hole up to floor level in preparation for applying Mapei Latexplan No Ammonia self-levelling compound throughout the hallway before laying laminate flooring.

I’m using this compound because the hallway previously had asbestos floor tiles, which have now been removed, leaving bitumen behind and this compound I have used before and is suitable for that requirement.

The hole measures approximately 14cm deep, 7cm wide, and 41cm long. It has a cement base at the bottom and brickwork towards the front. Around the top of the hole is a black plastic-type material, which I believe to be a damp-proof course (DPC). From the top of this DPC, there’s a further 2cm gap before reaching the main floor level.

Could anyone please advise on the best way to fill and prepare this hole so it’s ready for the self-levelling compound?

I am also concerned with the fact that this hole has no DPM and would like advice about if I should 1

Many thanks!

 

[blup]

Hi, thanks in advance for any advice.

When we had a new front door installed, we also removed a low wall that previously sat beneath a window. This has left a hole in the floor, which is part of the cavity wall. I now need to fill this hole up to floor level in preparation for applying Mapei Latexplan No Ammonia self-levelling compound throughout the hallway before laying laminate flooring.

I’m using this compound because the hallway previously had asbestos floor tiles, which have now been removed, leaving bitumen behind and this compound I have used before and is suitable for that requirement.

The hole measures approximately 14cm deep, 7cm wide, and 41cm long. It has a cement base at the bottom and brickwork towards the front. Around the top of the hole is a black plastic-type material, which I believe to be a damp-proof course (DPC). From the top of this DPC, there’s a further 2cm gap before reaching the main floor level.

The dpc is the dpm, just overlap the new with the existing then apply the levelling compound.

Could anyone please advise on the best way to fill and prepare this hole so it’s ready for the self-levelling compound?

Before doing the above obviously fill the cavity below first, Screwfix and Tool Station do a repair mortar product (Bostik cementone) that is workable but sets quickly.

I am also concerned with the fact that this hole has no DPM and would like advice about if I should 1

The membrane appears to be what you describe as the dpc. The dpc runs under the brick and block work in the main walls. They should overlap.

Many thanks!

 

[Danny Hardy]

You cant put their floor leveling compound straight over a DPM, I have asked Mapei, I am considering filling the void with hardcore, tampered down, then adding sharp sand to level it out, adding a dpm to the surface as you say, over the hole and hardcore/sand, overlapping, then use a concrete repair mortar to fill the rest of it up to the main floor level, then the floor leveling compound can go over the whole lot, floor & concrete repair, once the concrete repair is primed

 

[dazlight]

best way would be remove all that old Dpm
Then put some visqueen sheet in and lap it up the door. Then fill in with the Mapei na and granno chips.
I’d then Dpm over all that with an epoxy Dpm but you could just screed it all with the na then use a decent underlay with taped joints.

 

[Danny Hardy]

Hi Dazlight,

Thanks so much for your advice and response – I was actually considering something very similar.

My plan was to line the hole with a U-shaped DPM, as you suggested, then fill it with MOT Type 1 hardcore, compact it thoroughly, and add a layer of sharp sand on top to bring it level with the rest of the floor. I’d then place another DPM layer over the top.

After that, I was thinking of applying a bonding slurry (cement, water, and PVA) to help the new concrete adhere to the old, and then fill the remaining section with general-purpose concrete to bring it flush with the existing floor. Once that's dry, I’d prime the area and apply Mapei NA across the whole floor before laying the underlay and laminate, just as you recommended.

What do you think of that approach?

I am thinking having fresh concrete sitting over the DPM sheets would be ok, I think this is how they do it when they lay a new floor anyway, Mapie NA not so much. The new concrete should hopefully bond well with the sides and floor where their is old concrete with the help of the slurry, forming a sort of slab.

My only concern with your suggestion is the compatibility between Mapei NA and an epoxy DPM. From what I've been told by Mapei, none of their primers or smoothing compounds are suitable for use over liquid DPMs, although they can be used over bitumen without primer, or over bare concrete if primed with Mapie Primer G. That makes things a bit tricky.

Also, I’ve been asking around, and I'm still wondering – why does everyone keep recommending Visqueen DPM? It seems really expensive for the small amount I need. Isn’t there a more affordable DPM alternative that would do the job just as well?

Lastly, is there a specific reason you suggest removing the old DPC rather than simply overlapping it with new material?

Thanks again!

 

[dazlight]

You could use a builders rubble bag. Done it loads.
It’s to stop any water / moisture getting through under the door frame.
Any moisture tolerant compound is fine. Not sure who you spoke to at Mapei as their na is and can go under liquid Dpms.

I do my way as it dries quickly.

 

[Danny Hardy]

Can you link an epoxy DPM that you are sure the Mapie NA can go over for me please? I know Mapie NA can go under liquid DPMs but your suggesting fill the hole, epoxy DPM over the top of that now filled hole, then put the Mapie NA again over the top of the epoxy DPM right? and my concern is it then bonding with the epoxy DPM under it or am I not understanding you correctly? Thanks

 

[Danny Hardy]

Ok Daz, I just looked at the datasheet for the Mapie NA and it does indeed say

Latexplan No Ammonia is suitable for levelling differences in thickness between 3mm to 10mm on new and
existing substrates. It can be used over most existing adhesive residues, including bitumen. Also suitable for
use over plywood substrates and MAPEI surface applied DPMs in most cases without priming

However the Mapei DPM looks very expensive so if you know of 1 that I can use please let me know

 

[Danny Hardy]

Hi Dazlight, I was looking at the datasheet for the Mapei NA last night and realised that its only supposed to be for smoothing differences of between 3mm - 10mm which sounds like a bit of a problem?

I know you suggested adding granno chips so I assume thats because the hole is deeper then that? also from the top of the hole -> main floor level ranges between 1-2 1/2 cms which is to much for standard NA

 

[dazlight]

Does the rest of the floor gave a Dpm ? How old is your house.
How many m2 is the hallway.

 

[dazlight]

3kg Fball F77

 

[dazlight]

I can’t see any visqueen Dpm in your pictures ?

 

[Danny Hardy]

No there is no Visqueen DPM. I have not touched any of it yet or done anything with it, we just have a bare hole and the exposed DPC

I am not sure if there is any DPM under the concrete floor however I believe thaty the bitumen you can see acts as 1? I will be adding an underlay that has a DPM

The house was built about 1960s

The hallway is about 4.2 square meters.

Is the reason you suggested using the Mapie NA to level the floor upto floor level and not using concrete just drying times? I am really in no rush, I can wait for conrete to dry fully, especially if its a better solution considering the depth being 1-2.5cms, can I pour concrete over the Fball F77 expoxy DPM?

Thanks

 

[dazlight]

Ok fill in concrete then.
Then the na over the whole floor at 3mm
Fball f77 3kg / ardex DPM1c 3kg
Then the underlay & laminate

 

[dazlight]

1st thing to do is remove anything loose