Self compacting concrete

[Nickfromwales]

41 minutes ago, Oz07 said:

I dont understand all the hate for self compacting here. Ive used it on every house I've built. Whether its ground bearing slab or being used as a "screed" ontop of b&b. Always had the wagon back right up to the house and pour it in. Rake it about, dapple bar and get the sealer sprayed on. Very flat and has always been level enough as I've always poured to the top of the blockwork at dpc level. Back in the lafarge days they sent a rep/concreter out inc in the price to help you with all the gear. Last lot I had needed to pay a guy to help who the concrete company reccomend. It certainly doesn't do the job for you but its a lot easier and better flowing than normal concrete. 

It's not hate.

 

It's a pragmatic discussion involving some strangers on the internet  

 

I just doubt it's necessary, and my advice not to DIY is caused by the shiver that goes down my spine when someone, as a complete novice, thinks that this product will in any way make this easy or 'lay itself'. 

 

Regular concrete and a dapple bar, a home-made one at that, will be all that's needed. (IMHO).

[Iceverge]

On 16/02/2026 at 17:48, lizzieuk1 said:

Does anyone know if there's any reason you can't  use self compacting concrete in an insulated raft? 

(Not talking about flow screed types)

 

I did a bit of reading.

 

It's apparently very sensitive to getting the slump exactly correct. Small variations of temp can make it difficult to work. 

 

Also because it's so runny you need to hermetically seal the EPS or you'll have leaks of watery cement paste and it'll make the concrete crumbly. 

 

Normal concrete seems a better fit. 

 

[Nickfromwales]

1 minute ago, Iceverge said:

 

I did a bit of reading.

 

It's apparently very sensitive to getting the slump exactly correct. Small variations of temp can make it difficult to work. 

 

Also because it's so runny you need to hermetically seal the EPS or you'll have leaks of watery cement paste and it'll make the concrete crumbly. 

 

Normal concrete seems a better fit. 

 

Even with normal concrete it can be a nightmare. Most are simply too keen to get the wagon emptied out, so the next one can back up and empty that too. No time for the slump to be properly checked unless you're ferocious in insisting this gets done for each wagon. And then, if it's not right, you need a plan B in place ready to effect.

[Iceverge]

 

 

I must admit it does look good.

 

Mentioning of twice the material price in some places though. @Oz07 any insight here?

 

@lizzieuk1 maybe if you had a sheet of polythene inside the EPS and really boulstered up the shuttering at the outside you could get the SE on board. From what I read it's every bit as strong as normal concrete. 

 

Self build is where we push the envelope after all!!

 

 

 

 

[Iceverge]

26 minutes ago, Nickfromwales said:

Most are simply too keen to get the wagon emptied out.

 

That's a mistake you make once.

 

After dealing with a load of concrete drying in the wrong place once you learn to be robust with the drivers re waiting times and putting down their phone and backing the lorry up a few more ft to exactly where you need it. 

[torre]

1 hour ago, Iceverge said:

very sensitive to getting the slump exactly correct

Starting with which way up you fill the cone!

[Oz07]

8 hours ago, Iceverge said:

 

 

I must admit it does look good.

 

Mentioning of twice the material price in some places though. @Oz07 any insight here?

 

@lizzieuk1 maybe if you had a sheet of polythene inside the EPS and really boulstered up the shuttering at the outside you could get the SE on board. From what I read it's every bit as strong as normal concrete. 

 

Self build is where we push the envelope after all!!

 

 

 

 

It is good. Ive never had reason to complain about it. Never had to use SLC on it either its that flat. Always seal my dpm up well as like you say, its runny. 

Price wise it did used to be getting on for twice the price. But the rep helping you lay it was included in the price with all the gear they bring. It always made economic sense to me. 

[saveasteading]

14 hours ago, Oz07 said:

the hate for self compacting here

There is no hate. It's basically that a pump mix is being described as self compacting when it's simply very runny: a pump mix.

The raking and tamping are compacting it enough, but a poker brings out trapped airand moves the mix through any reinforcement and into corners... which is what compaction is.

 

But a pump is a beast to handle so not diy or for beginners. Poker not easy either.

Maybe we have different standards but my 'level' is very level and I want it smooth, and the quality controlled ( no added water) and properly formed contraction joints.

 

If it is to have a further construction of screed and insulation over it then a diy job may suffice.

[Oz07]

7 hours ago, saveasteading said:

There is no hate. It's basically that a pump mix is being described as self compacting when it's simply very runny: a pump mix.

The raking and tamping are compacting it enough, but a poker brings out trapped airand moves the mix through any reinforcement and into corners... which is what compaction is.

 

But a pump is a beast to handle so not diy or for beginners. Poker not easy either.

Maybe we have different standards but my 'level' is very level and I want it smooth, and the quality controlled ( no added water) and properly formed contraction joints.

 

If it is to have a further construction of screed and insulation over it then a diy job may suffice.

Have you seen proper self compacting concrete? Im not just talking about a wet normal concrete. There is 10mm agg, admixtures and fibres in the proper stuff. Ive never had water added to it and the last batch I had came from what was at the time one of the most advanced batching plants in the UK. There was an article about it before a national bought them out. 

Edited 7 hours ago by Oz07

[saveasteading]

48 minutes ago, Oz07 said:

Im not just talking about a wet normal concrete

No I'm assuming it is, or is similar to,  a pump mix, so has a plasticiser or super-plasticiser and small aggregate.

From further reading it looks to me as if we are talking about the same sort of mix but with different terminology.

 

I'm surprised it can include fibres as they tend to clump and make the concrete very sticky to handle, but maybe with the plasticiser and very prompt use, that is overcome.

I'm guessing now, but would also expect that it is easier with small and rounded gravel than with crushed quarry stone.

 

I'm pretty sure it will not be self -levelling which brings us back to the original question.

 

Do you have any info on the relative cost and any disadvantages?