Installing concrete floor

[Eddy_H]

Hello, I’ve just started digging out a concrete floor to replace a worn out slab and was hoping to get a few pointers regarding the install.

30m2 floor area and I’ve planned;

1, Compact the sub-soil 2. 100mm MOT compacted 3. Sand blind and lightly compact 4. 1200 DPM 5. 100mm Eco-Therm insulation and 19mm perimeter insulation

6. 100MM C25 concrete to around Finished floor level.


Access to property is restricted and wheel barrow can’t get through FRont or back door. I’ve spoken to a local concrete company who can supply, pump and level the slab for around £1500.

My main questions are

1. I’ve read that you won’t be able to place laminate flooring or carpet directly on the slab as it’ll be too rough, can anyone suggest the easiest way to get the slab smooth enough?

2. I am planning to support the stairs with some sort of brick or wood pad placed between the stringer ends and the insulation. Can I just leave this in situ and embed it in the slab once poured ?

Any help would be appreciated.

 

[Jaygray]

I'm not a builder so take this with a pinch of salt.

Concrete floor is an easy one. Put some self leveling compound down after the pour. Very diy friendly.

Re the stairs, I'm planning to do the same. Bit ill use a concrete terma block. Easy the but to size and lay.

Have you considered running all your power an water supply in Central guttering tj make it easy to change/ run bee cable in the future?

 

[Eddy_H]

I was hoping that you could simply pour a thin layer of levelling compound on the floor to just cover the surface stones, but I wasn't sure it would actually stick to the new floor and not crumble when walked on. Mind you, it would need an awful lot to cover a 30m2 area.

I can get away with surface mounting my pipe work but it would be neater buried, it's something I need to think about. The gas pipe needs to be encased in the actual concrete as far as I'm aware.

My main aim was to get away from having to have someone out to do a separate screed, hence, having concrete on top of the slab. It's a shame you can't screed it in sections like they do when plastering a wall,using battens to screed off

 

[Jaygray]

If you prime it, it will stick. This is fairly common and what the builder did on my extension.

The other option, which might be harder and more expensive is to have the concrete polished. But I'd only do this if you were planning to display the concrete floor.

Burried would be better. More importantly, what are you going to do in 5 years if you want to add another socket or radiator? This is what has put me off making the switch.

 

[Eddy_H]

A option someone mentioned to me, but sounded a bit of a bodge, was to put the slab over the dpm, a layer of sand on top and bed the insulation on the sand,then caber deck the floor?

 

[Eddy_H]

This is the first house I've had with a concrete floor, it's proving to be a real headache, so much easier with a suspended floor

 

[23vc]

A option someone mentioned to me, but sounded a bit of a bodge, was to put the slab over the dpm, a layer of sand on top and bed the insulation on the sand,then caber deck the floor?

As long as the main ground bearing slab is done right, then you can make up whatever on top of it. The dpm would need to fully enclose the insulation and floating floor though so might end up more hassle and it’s not normally done like that.
When i did mine, which was about the same size as yours, I made it so when the slab was poured it could be tamped dead level against 2x2 formers, which gets it fairly close, then a few hours later when it could just take my weight stood on a bit of board, went round the entire thing and troweled the hell out of it with my plastering towel, which was hard work, but resulted in a really nice smooth finish, not a typical dusty aggregate concrete finish. Did it again since on a garage. It’s a bit of a ball ache but works for me.

Still had to do the odd patch of SLC to get it bang on (SR1 3mm tolerance?) for large porcelain tiles but that was dead easy and was only a couple of bags.

 

[stevie888]

You'd normally screed a slab and a good screeder will produce a finish that needs no levelling.

If you don't want to do that then a powerfloat used properly will give you a suitable finish

 

[23vc]

Agree on the screed, but having done both over the years the slab finishing method I described above I’d say is DIY’able, a decent S&C (or pumped) screed much less so!

 

[endecotp]

2. I am planning to support the stairs with some sort of brick or wood pad placed between the stringer ends and the insulation. Can I just leave this in situ and embed it in the slab once poured ?

Here’s a previous thread about this:

T

Thread 'Temporary/Permanent stair support for insulation & UFH'

17 Sep 2025

I'm replacing my suspended floor with a concrete one, and have just poured the slab. The plan now is 150mm PIR, UFH pipes, and 50mm liquid screed.

The stairs are currently supported on a temporary 6x3 timber which allowed me to pour the slab straight through (picture below). The stairs need supporting on the stringer by the wall, and the post.

How should I support the stairs permanently?
1 - Directly on the slab. Wood? Brick? Something with a better U value? I would then insulate around the supports and pour the screed around them.
2 - Create a new temporary support that will allow...

• twillmo
• floor construction insulation slab stairs
• Replies: 20
• Forum: Building

I think others have asked the same question; search the forum.

 

[Eddy_H]

In terms of compacting the sub soil and MOT, I'm concerned about using a whacker plate in and around the house walls, talking to neighbours, I think these properties have had issues in the past. The sub soil looks really loose, you can dig it with your hands easily.
I've never used a whacker plate before, so I may be overthinking it, but would using a garden roller be effective and gentler ?

 

[Deluks]

In terms of compacting the sub soil and MOT, I'm concerned about using a whacker plate in and around the house walls, talking to neighbours, I think these properties have had issues in the past. The sub soil looks really loose, you can dig it with your hands easily.
I've never used a whacker plate before, so I may be overthinking it, but would using a garden roller be effective and gentler ?

A roller won't really cut it, use a hand tamper in sensitive areas. In the past I've got by with a 4" fence post.

 

[Eddy_H]

So, I picked up Tamper from toolstation and used round the wall perimeters, whacker in room centers, all well and feels solid. I am now getting ready to build up the layers,

My proposed make up is 340mm ( 100mm hardcore, 25mm sand,100mm insulation, 100mm C25 and allow 15mm for laminate or tille ). I plan to use a SLC to smooth the concrete for the final surface to go on.

Is bringing the concrete up to 15mm below my absolute final floor height and levelling off a reasonable target for Diyers ? I was going to fit battens to level off from but the shape of the floor plan ( unders stairs, alcoves, vestibule ) makes this quite difficult. The firm who are supplying the concrete will arrange for a pump ( needed as there';s limited access ) and says the lads will level off as well for a couple of hundered quid....what sort of height/flatness tolerance would be expected on a poured / levelled slab ?

 

[Russanthonypowell]

sounds like you have to move a lot of material "out" by hand if theres no access for a barrow.
A floor spec that would give you the least amount of hassle may be
compacted earth formation (yes this can be adequate) 1200mm gauge visqueen 100mm (70 kPa strenth) insulation, 500Gauge membrane Min 40mm Liquid screed. the screed is pumped and is a superflow which gives you a level for carpets, tiles, timber flooring..
Just one note to consider is the drying time for the liquid screed (by this I mean before you can tile, you would be able to walk on it next day) can be quite lengthy espesially if gypsum based. equally a win win for this could be a cementious based screed is stronger and less drying time.

PS perimeter insulation required as standard.

 

[Eddy_H]

''sounds like you have to move a lot of material "out" by hand if theres no access for a barrow''

I've had the week from hell, already filled 2 x 10 ton skips, that's by filling 2 x rubble buckets and loading to a barrow outside front door. There is still half the floor area to go ! My hands are wrecked.

There's no hardcore or concrete in your make up ? To be honest, now I might as well continue and see it through, Dig 340mm, 100mm hardcore/insulation/concrete. My big concern is the lads getting the concrete level because I'm aiming to smooth it with a couple of mm self levell compound and I haven't got the clearance under door frames to start compensating for 20/30 mm high spots after the pour.

I understand now, why only one local company even bothered to come out and quote for this job and even they don't seem to want to do it, easier ways to make money than this.