Self compacting concrete

[lizzieuk1]

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)

[JohnMo]

Possibly, but you need to go to your structural engineer to ensure it is of a suitable structural strength.

[Mr Punter]

I can't see why not.  It may be a fair bit more expensive and although it is self compacting, it will not necessarily be level.  I would get a decent concrete contractor and use standard concrete.

[Russell griffiths]

Have you looked into the availability 

when I thought about it briefly it wasn’t available locally so that stopped that idea. 

[lizzieuk1]

1 hour ago, JohnMo said:

Possibly, but you need to go to your structural engineer to ensure it is of a suitable structural strength.

I have asked if we can use scc and they have said no but, not given a reason. AFAIK the scc is made to the required strength(in our case C25/30) but has added platiciser to improve flow, I don't think it affects strength but, I'm certainly no expert, just reading up on the Internet concrete sites for info and so far that's what I've understood.

[lizzieuk1]

44 minutes ago, Russell griffiths said:

Have you looked into the availability 

when I thought about it briefly it wasn’t available locally so that stopped that idea. 

Yes, we have a local company that can supply it and, its not much more than standard. A standard mix with crew comes in around £500 more, not much so we will use that if it is the best option.

[carlos21]

whats self compacting concrete?

[JohnMo]

49 minutes ago, lizzieuk1 said:

and they have said no

So you can't use it then, you can ask the reason, but doesn't really change anything.

 

What the fascination of SCC?

[lizzieuk1]

2 hours ago, JohnMo said:

So you can't use it then, you can ask the reason, but doesn't really change anything.

 

What the fascination of SCC?

I've asked the question of why, my initial thought is they're worried that the eps profiles might suffer damage from the pressure of a more liquid flow. We can mitigate with shuttering if that is the only reason. I can't find any other real reason why it wouldn't be suitable, seems it has the same inherent strength as standard mix.

No fascination just a desirability to do as much of the build as we can and, this allows us to manage the pour etc, instead of needing a full crew to lay it. 

[lizzieuk1]

3 hours ago, carlos21 said:

whats self compacting concrete?

It's a mix that has added plasticiser, usually with a 10mm and below aggregate,  it flows more freely than a standard mix into mesh etc and doesnt leave air pockets. It doesn't require vibrating or power floating as compacts itself to a fairly level finish. May need a bull float to get the final finish but nothing more.

 

[Oz07]

8 hours ago, lizzieuk1 said:

It's a mix that has added plasticiser, usually with a 10mm and below aggregate,  it flows more freely than a standard mix into mesh etc and doesnt leave air pockets. It doesn't require vibrating or power floating as compacts itself to a fairly level finish. May need a bull float to get the final finish but nothing more.

 

You dont float it they just use a dapple bar all over then spray some sealer on it to stop the water on top evaporating. It certainly takes a lot of labour out of the process. Can also flow quite far with a diy shute, no pump needed in a lot of cases. 

[saveasteading]

13 hours ago, lizzieuk1 said:

have asked if we can use scc and they have said no but, not given a reason.

It's because this is a made up term.

Your contractor wants an easy life and isn't skilled at floating concrete, and doesn't  know that it's difficult and a real skill.

 

You must do what your SE says or otherwise agrees to.

 

The big danger here is that this contactor wants a plasticised mix thinking that will magically settle to dead level and compact itself.

My concern is their competence and then they'll add more water to make it even sloppier. The concrete won't be level, will be reduces strength and crack a lot.

[Iceverge]

There's no easy life with concrete and it takes skill to get it right. 

 

As much as plastering a wall in my view. 

 

Can you access good contractors for it, it's a real mess when it goes wrong as @Gone West can attest to? 

 

 

 

[Gone West]

3 hours ago, Iceverge said:

it's a real mess when it goes wrong as @Gone West can attest to? 

Indeed!!

 

 

[Oz07]

43 minutes ago, Gone West said:

Indeed!!

 

 

Why was yours cut up again?

[Mr Punter]

15 hours ago, lizzieuk1 said:

No fascination just a desirability to do as much of the build as we can and, this allows us to manage the pour etc, instead of needing a full crew to lay it. 

 

Concreting is one of the least forgiving trades on site.  For a house slab it is not worth the risk if you are a novice.  Spend some time finding a decent gang to do this.

[Nickfromwales]

16 hours ago, lizzieuk1 said:

No fascination just a desirability to do as much of the build as we can and, this allows us to manage the pour etc, instead of needing a full crew to lay it. 

Of all the places to have a go, this isn’t one imho. If this goes wrong, it’ll be spectacular.

 

Having any pour is manageable, but if you take charge then you accept full responsibility and liability, and can’t look to someone else to redo it at their cost if they feck it up.

 

I doubt the cost saving vs risk makes any sense here whatsoever.

[Gone West]

1 hour ago, Oz07 said:

Why was yours cut up again?

Twist the knife, why don't you 😀. I videoed the pour, and saw the concrete was going off before it was laid and there were voids forming.  We had the slab tested for voids and several were found, so they took core samples and condemed it. All because they wanted to save money by not having to use a pump. So much easier the second time. Fortunately it didn't cost us a penny, but we did lose a couple of weeks.

 

[saveasteading]

.

1 hour ago, Nickfromwales said:

us to manage the pour etc,

Manage? You mean you get some labourers and control them? But they're telling you to get this magic concrete?

 

 

For diy you could deliberately lay the concrete 25mm or so low. Then get a professional to screed later.

but beware, level control is a skill in itself.

 

Is there reinforcement?

[JohnMo]

For the cost of letting a company get on with it, there isn't much money to save by DIY, a lot of risk of fuc*ing up and getting an utter mess that isn't level, isn't flat etc.

 

The other thing is the effort needed, self leveling or otherwise, to think to can do it yourself is a dream, it's a team effort, controlling people that haven't done many times before - life is too short.

17 hours ago, lizzieuk1 said:

worried that the eps profiles might suffer damage from the pressure of a more liquid flow. We can mitigate with shuttering if that is the only reason. I can't find any other real reason why it wouldn't be suitable, seems it has the same inherent strength as standard mix.

No fascination just a desirability to do as much of the build as we can and, this allows us to manage the pour etc, instead of needing a full crew to lay it. 

Couple of points here

If the EPS is that fragile, the EPS design is not correct, if you need shuttering the EPS design isn't correct.

 

You have already stated your no expert, so not sure your experience or lack of, is an added value here.

 

Let the experts do the job, they are cheap for experts, build the walls yourself and save real money.

 

 

[Nickfromwales]

1 hour ago, saveasteading said:

But they're telling you to get this magic concrete?

I'm against the 'magic' stuff btw, and I've seen enough concrete pours go tits up to know it's not a job for the feint-hearted or uninitiated.

[saveasteading]

2 minutes ago, Nickfromwales said:

it's not a job for the feint-hearted or uninitiated.

It's so important that i would always attend when this was happening on our projects, even with proven expert  slab contractors. There is so much that can go wrong and the effects can be drastic.

The OP appears to have a designed slab by an SE, as a raft over insulation. so there will be reinforcement to fix accurately

 

@lizzieuk1. If the SE says no then it means no.

There is another unknown of course in the weather, when pouring in the open.  Rain, wind, baking sun... all problems. and then at 6pm a cat or fox will always walk over it.

I think we are all trying to gently say... diy what you can but not the slab, and beware that many contractors think they can do it, but don't know a lot.

Are you having underfloor heating?

 

[FuerteStu]

I used to work with civil formwork and concreting. Bridges, retaining walls and abutments mainly.. 

 

Self compacting concrete isn't what people think it is. For the most part it's used when you're unable to access to 'poker' and get rid of air pockets. (like 10 metres down in a bridge pier column, or in situations where it's dangerous to send a crew into an area like a confined space) 

 

Personally I wouldn't recommend it unless you HAVE to use it, the reasons to WANT to use It, simply a lack of understanding and skill. 

 

It would be a bit like listening to someone who said they can make money really quick, and taking you to a casino. Big gamble. 

[Oz07]

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. 

[Iceverge]

39 minutes ago, Oz07 said:

I dont understand all the hate for self compacting here. Ive used it on every house I've built.

 

I don't think the caution urged is anything against the SCC. More so DIYing an insulated slab without an experienced crew. 

 

I've never used it but it sounds ideal for pouring inside rising walls as a subfloor for example.