Concrete floor pouring advice

[Coll659]

Hopefully the last time I bother you all with my floor. Next week I will be pouring the concrete floor in the house in renovating and looking for advice and tips. It's an old house with stone foundations, I dug out the old rubble that the old wood floor was sat on until I got to compacted ground and now have the following:

 

 -sand blinding

-30mm eps

-Dpm

-Insulation (200mm EPS in some places and 100mm PIR in others) 

-underfloor heating foil

-underfloor heating pipes stapled to insulation

-4mm composite rebar 150x150 on 50mm chairs

-30mm EPS insulation around edges and an expansion foam skirt

 

I'll be getting the concrete delivered with a pump truck and hoses in one go. The main entrance is marked with the red arrow in the picture before, I'll start in the back room and work my way towards the entrance. It's approx 110m2 in total. 

 

 

My questions are: 

 

How do I make joints between the rooms taking into account there will be underfloor heating pipes going through doorways. Should the slabs be completely separate for each room to avoid cracking and allow expansion? 

 

What advice and tips do you have to successfully pour it all. It will be the finish floor (just tiles and laminate going on top) so I need it smooth and level. I guess I need long straight pieces of wood or something for screeding. Should I make one for each room the full width of the room for screeding? but what do you normally use to screed from (like rails) 

Then a bull float and keep working back through the house to the entrance. And then I believe after it starts to dry a little you trowel it up? How long after pouring is this normally? 

 

Any advice or tips would be great. 

 

 

 

 

[Redbeard]

Where or what is your Vapour Control Layer? The only thing I can see in the right place is 

35 minutes ago, Coll659 said:

underfloor heating foil

If that's a VCL is it taped to within an inch of its life at all joints, penetrations and perimeters?

[Tom]

Apologies if I'm late to the game here, but do your walls have a DPM? Have you considered the risk of rising damp in the walls?

[Redbeard]

Out of interest, why 30mm EPS below the DPM?

[Coll659]

41 minutes ago, Redbeard said:

Where or what is your Vapour Control Layer? The only thing I can see in the right place is 

If that's a VCL is it taped to within an inch of its life at all joints, penetrations and perimeters?

From what I understood the underfloor heating foil does this job? But I will look more into this thanks. 

 

And yeah the walls have an old dpc (the hard tar like one, forgot the name of it right now?) it's old but doesn't seem to be letting any damp up through the walls and it has been empty and in heated for quite a few years. You can just about make it out in the picture below

[Coll659]

Just now, Redbeard said:

Out of interest, why 30mm EPS below the DPM?

Just to protect the DPM

[Redbeard]

10 minutes ago, Coll659 said:

Just to protect the DPM

It's a tiny point, but that's arguably what the sand blinding is for. I guess no harm having belt and braces!

[Iceverge]

I would recommend you get some experience help with this as it'll be a mess if it goes wrong.  What kind of team have you currently lined up? 

 

You could build an expansion joint into the doors to allow it to crack there. 

 

I wouldn't fret too much about DPC's in the walls but would ensure that the localises water table is well below it. 

 

You might need to add a french drain to the house if it isn't. 

 

The rest of the plan sounds fine. 

[Coll659]

Thanks for the advice. 

 

Currently I have a few people who have no experience but are useful for lugging around hoses where we need them, then there's me and one or hopefully two more people who are not professional builders but pretty good with this stuff and some experience of building work. I will see if I can get someone with experience but not sure if that will be possible yet. 

 

I'm thinking to use 100mm eps in all the doorways, set to the level of my concrete and put outer conduit pipe for my underfloor heating pipes to pass through, and tape up the ends. This will then make each room completely separate with it's own slab. I can then just put my flooring straight over the EPS. 

 

The water table is pretty high but the foundations come up above the ground quite a lot so my dpc and floor layer is well above water table. But I am also in the process of digging a french drain as well. 

 

Looking at local rental shops and see they have the vibrating bull floats and wondering if it's worth hiring one or just using a normal one

[torre]

Not something I've done lots of but this looks quite challenging to me given all your walls are in place and you've got to work your way out via three or four rooms, much harder than having access from all around the slab.

 

You've quite a lot of concrete and limited access and working time while aiming for a finish you can tile on. How are you setting your level throughout the building? You don't want high spots and I'd be prepared to accept being a bit low in corners that are hard to reach if you're feeling pushed for working time and budget for some self leveling compound. It looks tricky to get back through to trowel over too.

 

Would it cost much more to do two pours? looks like a single doorway divides the top and bottom of the floorplan. That might take the pressure off a bit and let you see how the first one goes. As @Iceverge said this is messy if it goes wrong.

 

[Onoff]

My 3x3m bathroom. I screwed "screed rails", (actually lengths of Unistrut), either side and made a tamping board. 100mm of wet concrete. Came out flatter than a flat thing.

 

 

[Onoff]

This is my room at the stage where the Type 2 hardcore on compacted ground had been sand blinded then had 25mm lain over it:

 

 

I squared of the old footings with shuttered concrete. The original tar DPC is at the top of the breeze block:

 

 

I then painted liquid DPM up to the tar DPC:

 

 

Then stuck 2" of EPS as perimeter insulation:

 

 

 

 

The went 1m up the wall with more DPM on the two external walls before studding:

 

 

[torre]

@Onoff nice job and that's closer to the size of floor I've done when renovating. The method works well, room or two at a time, even if inexperienced.

 

I don't think I'd have been confident to handle another 10 times the volume of concrete being poured in the next hour or two throughout the house though.

[Onoff]

Didn't someone on here get pumped, self levelling screed/concrete? You just pump it and it flows/levels itself to the required depth. 

[Coll659]

Thanks all for the advice. 

 

Definitely agree that the best advice is to not do it in one pour. Unfortunately for to a variety of factors i love if need to do it in one go. 

 

My plan is to cut all the perimeter insulation to the perfect level, plus the insulation in the doorways to level from. Perhaps a laser set up as well. 

[Onoff]

You could perhaps stick some eps blocks mid floor in the rooms to act as a level guide. Then dig out and fill later. 

[Coll659]

48 minutes ago, Onoff said:

You could perhaps stick some eps blocks mid floor in the rooms to act as a level guide. Then dig out and fill later. 

Good idea I'll consider that

[Onoff]

1 hour ago, Coll659 said:

Good idea I'll consider that

 

Worth a thought too if you intend fitting a flush shower tray anywhere. Leave a big square/rectangle with the waste coming into it. Big block of eps. Later you can shunt the tray and waste around. 

[Adrian Walker]

23 hours ago, Onoff said:

Didn't someone on here get pumped, self levelling screed/concrete? You just pump it and it flows/levels itself to the required depth. 

Yes, I used CEMEX Evolution self leaving concrete on a project, worked very well. 

[Nickfromwales]

On 12/09/2025 at 12:00, Onoff said:

You could perhaps stick some eps blocks mid floor in the rooms to act as a level guide. Then dig out and fill later. 

Better to use bits of batten going floor to ceiling with white paint and a datum marked on it? Can use a full length attached to the ceiling timbers and then cut and wiggle free just as the concrete goes hard enough to take foot traffic over walking boards?

 

EPS marker blocks will likely gets smashed / knocked off as the pour goes ahead, with zero time / opportunity then to reset them. Once a pour begins, you ain’t stopping it! Battens are then going nowhere, so with that and the perimeter insulation set up as datum’s the stress should be somewhat removed. 
 

On 12/09/2025 at 11:36, Coll659 said:

My plan is to cut all the perimeter insulation to the perfect level, plus the insulation in the doorways to level from. Perhaps a laser set up as well. 

Don’t do this, always have this higher than the pour, with a fat permanent marker line drawn on it from a laser line, and then cut off the excess later. If the pour happens to spill over the top (accidentally) then it’ll drop down and bridge your original DPC.

 

Where your original DPC is, I’d black jack the area, 100mm below, and 100mm above as insurance, as once you’ve poured there’s no going back. Use a 75% water / 25% mix of liquid DPM product to prime the areas that you intend to then brush the liquid DPC on to, as brushing onto friable masonry that has not been ‘sized’ will be a pita and it’ll pull off very easily. Priming will allow the product to soak into the surface, providing an excellent key for the surface applied layer(s). A good few £££ to go on this, but I’d be doing this if it were my place.
 

You might find that the dilute mix will go through a cheap electric HVLP gun, like one for spraying fence panels with preservative, which would make life a lot easier. If that works, just make a larger amount of the diluted mix so the gun is constantly ‘wet’ and you can refill without having to measure the solution each time; if the black jack begins to cure in the gun you’re fecked. 
 

If you set this job out, and prepare yourself, you can likely do this in one sitting, but if you’re 10% off in the prep and sequencing then it could very well go 2 pairs of tits up.

 

On 11/09/2025 at 16:20, Coll659 said:

I'm thinking to use 100mm eps in all the doorways, set to the level of my concrete and put outer conduit pipe for my underfloor heating pipes to pass through, and tape up the ends. This will then make each room completely separate with its own slab. I can then just put my flooring straight over the EPS. 

No need for 100mm, just use 25/30mm PIR and then the expansion perimeter / edge insulation either side for your expansion relief. That edge insulation towns corners just fine, so aim to have the middle of the PIR directly where the door will reside. 
 

No need to install the conduits afaic, and I’ve been doing these jobs for decades.

 

All you (actually) need is simple foam up-stands there, but they get battered during a pour. I’d say stick with the block of insulation there and use that to get the doorways poured cock-on, (as you’re DIY’ing). 

[saveasteading]

I'm panicking for you. That concrete will come faster than you can level it.

Then it's too wet to walk on for a few hours for any precise work....until it's not, at which stage it is getting hard and difficult to improve. 

 

Cracking isn't your biggest worry. Di not allow any extra water in the mix. It will crack jaggedly at the doors but it doesn't matter.... or you lay a bit of hardboard in the surface to make it crack there.

 

As above, fix level markers to the walls and also in the middles they can come out again.

 

How many loads? 2 I guess.  Give yourself at least an hour between them, perhaps 2.

 

A shovel each and a bull float.

Polythene over the lot once you can walk on it.

[Nickfromwales]

I’d go level -3-5mm as your target, and then SLC each room to get it spot on, if you insist on DIY. 
 

Or pay a liquid concrete company to do the pour and admit this is a huge undertaking to get flat first time as a DIY project.

 

Some battles you can’t avoid, others you can pick and choose. Professionals will pour this in one go and get it pretty damn near perfect for you, with zero stress, plus the onus is on them to get it within their stated tolerance.  

[Spinny]

You don't say how thick the concrete is going to be ? 

(We had our pipes tied to the mesh rather than the insulation and had a polythene vapour barrier)

I'd have thought you need a detailed military plan for the day with some possible fall back options and everyone pre-briefed.

Talk to the concrete company to try to understand exactly what to expect from them. We ended up with an old pump lorry because the newer one was in for servicing, no flow control at the outlet end of the pipe, people had to shout and wave hands across a 30-40m distance to get the pump turned on and off. A significant delay between off and the flow ebbing away. At the beginning you can get a very watery slurry coming out of the pipe at first, so might possibly want to consider dumping this somewhere (out of a doorway or window or into wheelbarrows or something ?). At the end the concrete remaining in the pipe has to come out, so you might want to have a plan for where this can be dumped - we ended up with a considerable concrete mass on our driveway until we eventually got the builder to remove it. Know where the mixer and pump lorry are going to park and ensure it is clear of vehicles. Have plastic sheeting and tarps available so you can protect the road/driveway as necessary from leaks that may occur under the lorries. Know what the options are with the concrete company if things were to go wrong - lorry arriving late or early - having to abort part way through (will they then empty onto your property regardless etc) - job taking longer than expected. Check those volume calculations and know what you are going to do in case of shortfall or surplus.

Have boards avalable - we had a 6m board spanning our footings from one side to the other - not sure how that works for an existing building. Do you just work back from the far room, or is it feasible to do one corner room, then move to another corner room while someone is finishing/checking the first, then move back etc - I have no idea as I've never done it. Do you assign a person to each room ? Who does what exactly ? Will they be dressed appropriately - our builders young lad turned up in shorts and shoes and had to have concrete washed off his legs FAST to avoid concrete burns - brickie turned up in long protective trousers, gloves and wellington boots with shovels.

 

Pipes full of concrete are heavy and they can jump about a bit when the pump is running so make sure the pipe itself doesn't damage anything. I had to put some bits of insulation around the corner of our house to protect it.)

 

I am sure you must have any conduits, drains, manifolds, services in place - u/floor heating pipes pressurised - perhaps your cabling and plumbing pipes are going in the ceiling and walls ?

 

Keep the egde insulation higher. 

 

Levels can be tricky - have you used a water level to double check them - maybe know what your tolerance might be at doorways.

 

Splitting the pour may cost money - but how much money is it going to cost if things go wrong - likely an awful lot more.

 

Edited 14 hours ago by Spinny

[Spinny]

1 hour ago, Nickfromwales said:

Once a pour begins, you ain’t stopping it!

This.

 

And too high is too high - you are ****ed. But too low is fixable with levelling compound.

Edited 14 hours ago by Spinny

[saveasteading]

7 hours ago, Nickfromwales said:

Some battles you can’t avoid, others you can pick and choose.

I've been a contractor for decades and seen hundreds of big slabs going in.

I have seen enough to know that your plan worries me. 

 

I will step in to help or for interest in most processes but have always kept out of the way during this because it is skilled and brutal at the same time.

Good points made above.  eg the pipe is full of stone and is stupidly heavy as well as kicking around. The guy on it is usually  a super-fit 30 year old.

Consider buying 3 barrows and hiring 3 labourers instead of pumping.... you win control too and can compact and level as you go.

You will need scaffold boards to move around on.

 

Washdown at the end is a horrible, filthy job, especially the inside and outside of the pump pipe.

 

I mentioned this post to my daughter (Contractor , Project Manager, Architect).  Her jaw dropped and she immediately thought of the risks. One she added was how well your insulation layer is covered...…  the membrane must be intact and completely sealed at all laps, otherwise the concrete forces through and the insulation floats to the top carrying your reinforcement with it. I have seen this happen. Check your laps and tape as necessary one more time.

 

BUT seriously consider postponing this and getting a professional gang to do it.