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Insulation, UFH, conduit and Slab



Day 31 of the build. (this is taken from the day we started shuttering the foundations)

The weather up North has been spectacular for about 3 weeks, so we (Mandy and I) pushed to prepare and pour the slab before the weather changed, as I'm sure we will get a few weeks of low pressure, wet changeable weather after this spell.

Following on from the foundation ICF walls, I'd already loaded around 20ton of 40mm to dust in a pile the slab area. Sat on the sand blinded radon barrier.

Job one was to sort the drainage. I'd posted previously about my plan, and some constructive comments suggested changing my planned route, but with the extra length of run to the drain invert level I would have had to increase the floor height even more. So stuck with my original sketch. We ran string lines to mark the main areas, namely WC, SVP in the plant room, shower, WC and Bath, a need ran the drainage to the locations, as the utility backs onto the plant room I didn't add a drain in here as I'll run through the stud and use the SVP. Once the drainage was in place and is tested. We spread out the hardcore and compacted it. I used 10mm crush and run to bed the drainage and cover the pipes, I also ran ducting at this level, bringing in water, power, treatment plant feed plus some future ducts. 

To get the hardcore level / flat I used 3m lengths of galvanised conduit set on mortar pads all level to each other and used a 4M ally beam to screed the slab.

I compacted the first layer then used another screed pass to fill in any deviations and used this as the level for insulation.

I used a combination of 200 mm EPS 70 (50mm sheets and 100mm sheets all layed to stagger the joints, and used foam to seal to the ICF.

The top layer was 100mm EPS150 this gives a firm hold for the UFH staples, and a firmer feel to the insulation layer.




We plan to use a large shower tray and have this level with the floor, so I made this area sunken with two layers of EPS150 and a layer of 50mm PIR.

As we were installing the insulation I installed 2 * 100mm ducts for the ASHP in the second layer of insulation these were only 800mm long, and a duct for cables.

I also added flex ducts in the insulation for Hot & Cold services to the kitchen, utility, WC,Shower,bath, all these were cut using a hot knife.

Lastly I cut some pipe for floor sensors  in the kitchen, lounge, bedrooms and bathroom.



The underfloor heating consists of three loops around 95M length, planned using Loop cad.




The manifold was plumbed , filled and a pressure gauge to ensure no leaks. We have good water pressure so could pressurise to 6 Bar. ( With the heat ☀️ this rose to 9 bar one day).


The above picture also shows  K Steel screed rails. I used these to break the slab into smaller bays, and mainly will be under stud walls. The slab will for the foreseeable future be our finished floor, so I wanted to introduce expansion joints and force any cracking to these locations🤞.


I also used Tibmix metallic  dry shake topper on the concrete, the dry shake should help suppress the fibres and also increase the surface hardness. 

The pour happend on Friday 16th June, the first 5cube arriving at 8.30.  we did the kitchen bay first which needed the 7t 360 to move / place the concrete, then, poured the WC / plant room and utility bay. This was an error, I wanted to pour the lounge next so both bays could be finished at the same time, but under the pressure of the pour took advice to do the awkward section next. This resulted in only a 3rd of the lounge bay having concrete, so this was spread out lower so the next load could fill the bay.

By the time the second load arrived, the kitchen and utility bay was ready for power floating. The pan worked well and I had some time to start edging the slab, the rebar didn't allow the power float to get to the edge of the slab. 

By 13.00 all bays were in and leveled, but not floated, but the sun was very hot, and the kitchen bays was getting hard rapidly, I managed to float this but was struggling to to get a perfect finish. 

To dry shake makes the surface hard and this was apparent, the lounge and bedroom bays floated better, and to the main the dry shake suppressed a lot of the fibres but there are still some visible. The kitchen bay was rock hard by the time I managed to float again, and although it is fairly flat you can see, but not feel, the path of the power float.

I used Setseal 6 as an acrylic sealer, which seals the surface and  aids the curing process. By the time we finished the floor was rock hard, I mean hard, the idea being that the slab will slowly cure now but will not be affected by rain etc. Time will tell.


Due to the temp, and the float not getting to the edge, I will have to carry out some remedial work on the edges of the slab, as by the time I go to troweling these it was too late.

Today the slab looks great, it's flat and level, but the perimeter 2 inch will need some polishing, as will a section in the plant room.

I'm confident I can get this fixed. Time will tell.

The following picture doesn't do the slab surface any justice. It looks rough, but it's glass smooth.


So 10.5 cube of fibre reinforced concrete. Power Floated, and this was non stop until 17.30.

My chest and fore arms are wrecked from trying to tame the power float.


I'm a little disappointed in the edge finish, but looking at it another way, it's way better than if it would have started raining, or the wind that we have today. I'm sure a few hours with a wet diamond polisher will rectify the edges.  Maybe another hand would have been good. 🤔.


Onwards to the ICF walls...







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A like is insufficient. Brilliant rock snd thanks gog thd info.


Don't eorrh zbout the visible fibres  they zcuff off under the tiniest ftiction eg foot traffic.

Also the concrete finish looks fine. Try not to look at it and the appearance will improve. Some of the messier areas are surface laitence or froth marks from the coating.


Does your varnish completely seal the surface or do you need to wet it again?

The shrinkage cracks will be starting about now. Do not panic if there are any rogue ones.


A minor thought.....the shower and bath drains could go to local soakaways as Grey water, if that helps in any way.



Brilliant work though. Well done indeed.

  • Like 1
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16 minutes ago, saveasteading said:

Does your varnish completely seal the surface or do you need to wet it again?

It goes on whilst the concrete is still wet ish. And you can't cover with plastic as it can cause the sealer to bloom, it does suggest in extreme temps to re coat after 3 hours, so I did that at around 21.00 last night.

Edited by Jenki
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extreme temps to re coat after 3 hours, so I did that at around 21.00 




I know the stuff but only ever used it indoors.


There is a small risk of excessive evaporation out of the slab edges, esp once the shutters are off and if it is breezy. You could easily wet them if so inclined.

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This is inside the ICF, so no shuttering to remove, I did use some timber battens to protect the ICF from a vibrating screed. These are obviously staying where they are.... off to water the edges of my slab 😁

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Well done, concrete is always panicked suffering in my experience!

The ICF should give a very good PSI value at the wall floor junctions. 


Looking forward to a few more pics of the finished floor.

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12 minutes ago, Iceverge said:

Looking forward to a few more pics of the finished floor.

Let's see what the diamond polishing does😜

But that will probably have to wait, going to start on the walls while the weather is still good, so some OSB on top to protects it from the scaffolding. ( I'm putting it on the inside to help with bracing the walls)

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2 hours ago, Jenki said:

Let's see what the diamond polishing does😜.

I'd say don't bother. Relax for now and see how it turns out.  It doesn't turn out shiny like diamond, just abraded by fancy carborundum, and at great expense.

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3 hours ago, LiamJones said:

Great post, thanks. Where did you put your DPM?

It was a Radon barrier.

I put it under the strip footing then up and over the a pre hardcore base then drainage and services in a layer of hardcore then insulation. This way I didn't need to seal all the service penetrations for the Radon barrier.

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1 hour ago, saveasteading said:

Anything to report 2 months on?

Not yet. My workload is directed at the roof/ gables.  I'll get there, but not yet. I've also had to do a bit of paid work🤣

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On 18/08/2023 at 17:05, saveasteading said:

I was meaning, how does the slab look? Cracks, texture?

Sorry, I missed this.


Basically the slab is very good, I did put screed bars / expansion joints into the slab and the only cracks follow these lines.  around 90% of the slab is flat and smooth. the worst areas were the edges where I couldn't get the power float, and the sun  made finishing with a trowel due to drying  quickly impossible.

There were a few high spots which we have ground with a diamond disc, unfortunately this exposed more of the plastic fibres, the fibres used in out slab are around 50mm long 1mm thick and 2mm wide, so quite chunky things really, and the result of this is that there wont just wear away, and a blow lamps to burn them off is not satisfactory. So decision made - LVT flooring it is..



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1 hour ago, Jenki said:

the fibres used in out slab are around 50mm long 1mm thick and 2mm wide, so quite chunky

I've seen these but never used them. I've used the hair-like fibres and so have any readymix suppliers. It just rubs off underfoot.

Yours would rub off with a carborundum or a brick,  I'd think.


Anyway, it's saved how much on steel? A few hundred?

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