How to fill this gap : internal concrete floor

[Steve Campbell]

Hi folks. See below. In taking up carpet to get new floor fitted, this section turned out to be very weak mortar that was falling to pieces (the carpet grippers just fell out). Looks like this patio door may once have been a window and the builders just filled the floor space after the concrete slab with crap weak mortar. I’ve dug it out (not difficult !). Now need to refill….but….what with and how ?

Basic DIY’r here so looking for advice. I presume I can blank off the underneath and door frame with some damp course material as per half of it already so whatever I put in doesn’t stick to door ?

I don’t have a mixer…how much “stuff” will it take….presume some kind of concrete mix ?

Total dimensions = 4cm deep, 17cm wide & 180cm long
Thanks

[Vsix and Vtec]

Are you sure it was concrete you just dug up and not screed?

Either way, it won't take much. Half a bag of ready mix should be enough.

[119]

Vsix and Vtec said:

Are you sure it was concrete you just dug up and not screed?

Either way, it won't take much. Half a bag of ready mix should be enough.

Enough for what?

That looks quite thick and in front of double doors so would be nearer 2 bags.

[Steve Campbell]

Vsix and Vtec said:

Are you sure it was concrete you just dug up and not screed?

Either way, it won't take much. Half a bag of ready mix should be enough.

It was light brown like brick mortar but very weak...so definitely not concrete I don't think. I don't know the difference between concrete, mortar, screed to be honest ! I just want it to be a robust flooring for new LVT's going down but without messing up the door. The floor will be levelled with epoxy prior to tiles so it doesn't need to be perfect but what was there before was completely rubbish ! I could dig a screwdriver into it with not too much difficulty....it came out easily with a hammer and old screwdriver.

If anyone has a simple product that you think would work then please linky ! I make it 12-13000 cm2 or just less than 0.013m2 but I don't know how much that takes in terms of the products I've been googling etc. Yes it's double doors 180cm wide. Dimensions in the original post

Edited by Steve Campbell on Monday 22 April 14:24

[Rough101]

If it’s for LVT won’t you have plywood underneath? In which case is fill that with expanding foam.

I’ve done similar and it’s fine.

[Steve Campbell]

Rough101 said:

If it’s for LVT won’t you have plywood underneath? In which case is fill that with expanding foam.

I’ve done similar and it’s fine.

No it will be epoxy levelling compound on the concrete flooring.

[T1547]

Use this: https://www.tileexperience.co.uk/mapei-topcem-pron...


Pre-mixed rapid drying screed. Will give you a semi-dry mix that you can pack into the gap and trowel off flush with the surrounding screed.

[OutInTheShed]

I think you should understand what's what with damp course/lead tray under the door frame before flinging cement about.
This depends on what's outsdie too.
You might want a gap inside the frame, you might want a moisture barrier of some sort.
You want to avoid bridging the damp course etc.

As for filling the trench, I'd probably knock up a bit of concrete to fill it 5mm or so from the top and let that go off for a week, so the screed/levelling or whatever is not great thick lump that takes forever to dry and shrinks or some other disaster.

[James6112]

Steve Campbell said:

Vsix and Vtec said:

Are you sure it was concrete you just dug up and not screed?

Either way, it won't take much. Half a bag of ready mix should be enough.

It was light brown like brick mortar but very weak...so definitely not concrete I don't think. I don't know the difference between concrete, mortar, screed to be honest ! I just want it to be a robust flooring for new LVT's going down but without messing up the door. The floor will be levelled with epoxy prior to tiles so it doesn't need to be perfect but what was there before was completely rubbish ! I could dig a screwdriver into it with not too much difficulty....it came out easily with a hammer and old screwdriver.

If anyone has a simple product that you think would work then please linky ! I make it 12-13000 cm2 or just less than 0.013m2 but I don't know how much that takes in terms of the products I've been googling etc. Yes it's double doors 180cm wide. Dimensions in the original post

Edited by Steve Campbell on Monday 22 April 14:24

Hi
Are you getting someone in to lay the LVT or diy?
If the former, i’d ask them tbh
Whatever goes down has to be very dry/low moisture, before LVT goes down

[essayer]

+1 check with LVT fitter before doing anything

[dickymint]

essayer said:

+1 check with LVT fitter before doing anything

+2 in fact I'd leave it for him to do as he's the one that has to get the finished floor level.

[T1547]

OutInTheShed said:

I think you should understand what's what with damp course/lead tray under the door frame before flinging cement about.
This depends on what's outsdie too.
You might want a gap inside the frame, you might want a moisture barrier of some sort.
You want to avoid bridging the damp course etc.

As for filling the trench, I'd probably knock up a bit of concrete to fill it 5mm or so from the top and let that go off for a week, so the screed/levelling or whatever is not great thick lump that takes forever to dry and shrinks or some other disaster.

Concrete laid as thinly as that gap looks to be is likely to do exactly that - shrink and crack.

The product I linked to is polymer modified, shrinkage compensated and rapid drying.

Agree check the damp course arrangement/location.

[Pheo]

Isn’t the whole point of that gap that it’s a cavity wall and hence you need said gap to stop damp jumping across?

Think a cavity closer would be normal and then go over the top with the screed?

[Vanden Saab]

dickymint said:

essayer said:

+1 check with LVT fitter before doing anything

+2 in fact I'd leave it for him to do as he's the one that has to get the finished floor level.

This, I have taken the old tiles off and filled the holes normally gets the ' sorry booked up for months' response.

[dickymint]

Vanden Saab said:

dickymint said:

essayer said:

+1 check with LVT fitter before doing anything

+2 in fact I'd leave it for him to do as he's the one that has to get the finished floor level.

This, I have taken the old tiles off and filled the holes normally gets the ' sorry booked up for months' response.

I've pissed off a few plasterers by 'prepping' some walls

[AW10]

T1547 said:

Concrete laid as thinly as that gap looks to be is likely to do exactly that - shrink and crack.

The product I linked to is polymer modified, shrinkage compensated and rapid drying.

Agree check the damp course arrangement/location.

We're changing some of the cupboards in our utility room and I thus need to extend the tile flooring to areas that are currently bare screed. As the room has polypipe overlay UFH I'll need to add about 30mm of height over an area of 0.3 sq metres. The Topcem Pronto looks ideal and I'll need almost a bag but it appears I'll need to prepare the existing screed with a 2-3mm thick layer mixture of Topcem Pronto Slurry and Planicrete SP which are two further separate products? So I'll have loads of Topcem Pronto Slurry and Planicrete SP left which seems a bit of a waste? Or have I missed something? Would be grateful for feedback.

[Steve Campbell]

OK bit more investigation on my part. This is what I appear to have as current >


I want to put something to "frame" the infill against the door so the door isn't "stuck" to it. Was thinking I could use DPC sheet. So would I bridge across the foam as per diagram below (yellow) using DPC sheet or simply use the "orange" DPC ? Any tips ?


This product also seems ideal in terms of simplicity, only 1 bag required and self levelling as well : https://www.screwfix.com/p/no-nonsense-cement-base...

Thanks for comments so far. Hoping to get this done at the weekend.

Edited by Steve Campbell on Wednesday 24th April 15:08

[AW10]

That screwfix product looks useful but will require more careful shuttering.

[Steve Campbell]

AW10 said:

That screwfix product looks useful but will require more careful shuttering.

Does this mean the blanking off ? The area I'm trying to fill is already "shuttered" by the existing internal screed on the long edge & walls at either end. My question is more how to prepare the base and the door frame element. The "hole" is 4 cm deep, 180cm long and 17cm wide. I'm assuming the product will flow but it won't be like water and will be fairly viscous. Will I need to "tape" the DPC sheet I use so it doesn't move or something else ?

[AW10]

Yes, that's what I meant and I was thinking more about my application than yours; sorry.