Gavin’s isoquick foundation on clay soil

[joe90]

2 hours ago, IanR said:

The biggest yield improvement we saw on our arable farm, which is/was on Essex clay, was when we started mole draining in the late eighties. That wouldn't work either, if ground water didn't move through clay.

Well my reading of mole ploughing (which I was going to do in the soggy field next to my build) was that the mole creates a drain, like a mole hole, but works because it cracks the clay to create fissures allowing water to flow into the mole which should end up in a ditch of some sort.

[joe90]

2 hours ago, saveasteading said:

That's what i said , or implied.

 

Clever enough if there was a problem to overcome, but aiding flooding downstream.  Should not be a standard process.

But why? As long as the water table is below the dpm, or kept out by a perimeter membrane, it does no harm.

1/ Yes I got that 

2/ the amount of water moved by this was  very little and would not be considered adding to flooding (which never happened in the area), if it was not clay the same amount of water would end up in any sort of ditch or drainage anyway.it’s not like it was flowing water.

3/ being a keen gardener I disagree, plants (unless pond or margin plants) don’t like wet feet and I wanted to be able to walk on my lawn without wellies.

Edited October 16, 2023 by joe90

[saveasteading]

16 hours ago, IanR said:

quite possibly confirmation bias.

That's why I question everything, and enjoy hearing real rxpetitnces like yours.

That's why I looked into eps systems and costed one on a real job. The supplier gave a detailed quotation, and discounts.

It may not have suited that project which was not a standard house.

16 hours ago, IanR said:

Without a network in place, I costed both options for bringing in the required trades and materials.

Yes that's interesting. I can see this can work for genuine self build.

Quality is a huge issue. Even with known and generally trusted groundworkers, they are not as knowledgeable or caring as is desirable.

 

Backfilling the eps formwork with gravdl is sensible, to fill the void ompletrly and protect it. What I was questioning originally was a land drain a metre or so out from the perimeter.

 

I still question using porous / no fines sub base too. 

[Gone West]

19 hours ago, saveasteading said:

Quality is a huge issue. Even with known and generally trusted groundworkers, they are not as knowledgeable or caring as is desirable.

We had the first Isoquick system installed in the UK in 2010. It didn't initially go to plan. We fortunately videoed the whole thing. We had the type1 and fines extending out 750mm beyond the edge of the insulation all the way around the slab. These are entries from my blog at the time. Sorry about the quality of the pictures.

 

 

 

 

 

 

 

 

[gavztheouch]

Thanks for your post @Gone West

 

That does indeed sound like the nightmare scenario. Did you replace all the isoquick insulation? are you happy with the isoquick system now?
 

I’m thinking about pouring the slab anytime after next week maybe. This includes some cold months. I’ll prob need to wait until it is dry which normally means it will be cold. To get better weather I would need to wait until March at least. Has anyone poured concrete slabs like this in cold weather. Did you take any precautions?

 

 

[saveasteading]

3 hours ago, Gone West said:

had the type1 and fines extending out 750mm beyond the edge of the insulation

I appear to have been confused then, type 1 is near solid rock and not porous like single sized gravel which was my concern. This is sensible.

[saveasteading]

1 hour ago, gavztheouch said:

Has anyone poured concrete slabs like this in cold weather. Did you take any precautions

Yes. I've even dug some out again the next day. The weather had changed dramatically.

 

How cold do you mean?

 

If i recall, the magic temperature is 3° and rising. 

As soon as it starts yo drop again, beware.

Even then, the chemical reaction will be slow and it may be wise to delay.

A slab can take days to harden if very cold. 

You must not get frost in it. It must be covered with polythene as soon as it is hard enough to take even that without harming the surface.

 

You're better doing it on an overcast, even drizzly, day than very cold.

 

[IanR]

 

 

Ref. https://www.isoquick.co.uk/design-features

 

[saveasteading]

Thanks for the drawing. I see the note.

But type1 isn't free draining and it does contain fine particles. It has a formula of stone sizes such that it is as near solid rock as can be. Puddles form on it if well laid.

Back to my original point: I would not want water being encouraged to flow under my house, as single sized, free draining gravel, would.

 

I still find this very strange, and can't see why there isn't a polythene dpm.

 

All that aside. You have type 1 so that's perfect. Water won't reach your eps. Even if it did, nothing would happen to it.

 

 

[saveasteading]

Typically this style of design will use between 1/2 and 2/3rds of the concrete that would have been used in strip footings for the same building, 

 

That is a bold statement for a system where the slab might be 300mm thick. 

1/2 I doubt. 2/3 sounds feasible if the footings in the comparison are mass concrete.

 

It's obv much more complicated than that. I'd love to see that, and reinforcement, calculated. I'm not about to do it.

In any case, you were choosing a proven system for control reasons, not cost.

 

 

[IanR]

Layer 5 isn't Type 1, it's a "no fines" shingle/granite chippings layer and is typical for an insulated raft foundation and is only 30mm - 50mm thick.

 

Layer 6 is more similar to what you refer, although in this case is Type 3.

 

Water is not being encouraged to move under the foundation, it will do that if not mitigated against. Type 1 and Type 3 are porous.

 

On Isoquick the DPM is between EPS and concrete. I assume at ~200mm thick they're not expecting the UFH to be pinned to the EPS, as tied to the mesh would position it closer to the surface.

 

While Isoquick tend to go with a constant ~200mm thick raft, most others reduce this to 100mm thick for the majority and only go to +200mm at the ring beam, saving more concrete and further reducing the dig.

 

Personally, my choice was cost & performance.

Edited October 18, 2023 by IanR

[saveasteading]

I like the others even less in that case. They aren't using the structural raft principle, so are loading the eps more, locally.

 

They will need to be thicker at internal support walls as well as the perimeter.

 

Type 3 is indeed reduced (not zero) fines for a bit of drainage

Layer 5 is blinding, for level control. Industry standard is to use sand, but fine stone is much better. 'No fines' again is wierd  it can't be laid smoothly to levels, but I guess the eps compresses into the sharp and protruding stones.

 

As long as it works.

 

Excuse me when I mix up the parallel postings above Sometimes type 1, sometimes type 2.

I'm happy with either, then dpm, just not with gravel or no fines.

And why no dpm on the stone? That escapes me. Perhaps designed for different climates.

[IanR]

8 minutes ago, saveasteading said:

I like the others even less in that case. They aren't using the structural raft principle, so are loading the eps more, locally.

 

No they're not. The 100mm thick areas are where there are no load bearing walls. Rafts constructed to take high loads everywhere are over-engineered and wasting the client's money. It's an optimised product for cost and performance.

 

No DPM on the Type 1 is to avoid potential damage the DPM. You need the no-fines layer (which is just 30mm - 50mm thick) to stop water from thermally bypassing the EPS, as mentioned previously.

[Gone West]

3 hours ago, gavztheouch said:

Thanks for your post @Gone West

 

That does indeed sound like the nightmare scenario. Did you replace all the isoquick insulation? are you happy with the isoquick system now?
 

I’m thinking about pouring the slab anytime after next week maybe. This includes some cold months. I’ll prob need to wait until it is dry which normally means it will be cold. To get better weather I would need to wait until March at least. Has anyone poured concrete slabs like this in cold weather. Did you take any precautions?

 

 

IIRC all the insulation was replaced. Ours was laid in July 2010 so we had the opposite problem of higher temperatures, we were in Kent. We found the Isoquick system to be fine and it matched our wall construction well.

[Gone West]

2 hours ago, saveasteading said:

I appear to have been confused then, type 1 is near solid rock and not porous like single sized gravel which was my concern. This is sensible.

The 50mm layer of 3mm granite gravel just under the EPS should allow drainage if required. I was told the Peripor, which is made of very small granules, was more resistant to water absorption than standard EPS.

Edited October 18, 2023 by Gone West
changed fines to 3mm gravel

[saveasteading]

32 minutes ago, Gone West said:

gravel just under the EPS should allow drainage if required.

That's the thing. Why should it be required? 

A dpm costs about £100.

Granite over the same area, about £1,000?

I'm a bit shocked that non-sealed eps is available.

 

I'm sure your houses are fine. I'm just a bit annoyed that you could have spent a fair bit less.

 

For future people considering it, the several  savings I am thinking may not balance out any SE or Architect cost in refining the design.

 

PS.   Perhaps the concern is of the eps floating between installation and the steel weighing it down.

 

@Gone West thanks fof sharing  the slab story. Was this a package contract for the whole slab to that stage? Ending up at 3x the cost, and the delay.

Plenty of groundworkers would be capable of such a bad job. I have encountered many who didn't know how little they knew. Pump mix and pokers for compaction would be a mystery.

And yet they are out there still.

 

Concrete setting too quickly was presumably because they were taking too long to barrow it? Emergency "Stop ends" can be an essay another time.

[IanR]

46 minutes ago, saveasteading said:

That's the thing. Why should it be required? 

 

Please see my previous answers.

 

46 minutes ago, saveasteading said:

I'm a bit shocked that non-sealed eps is available.

 

What's "non-sealed" EPS?

 

46 minutes ago, saveasteading said:

I'm sure your houses are fine. I'm just a bit annoyed that you could have spent a fair bit less.

 

You're still not understanding the system.

 

46 minutes ago, saveasteading said:

For future people considering it, 

 

Talk to an experienced structural Engineer that understands and design insulated raft systems and their requirements, and, don't change the SE's details without their approval, otherwise their insurance wont cover you.

 

46 minutes ago, saveasteading said:

PS.   Perhaps the concern is of the eps floating between installation and the steel weighing it down.

 

There is, but not for the reasons you're assuming. With EPS on top of the DPM there is a risk of the concrete getting under the EPS if the ring beams are filled before the higher areas of EPS have been weighted, down with concrete on top. Happened to someone at the old place. The recommendation is to pour the concrete on to the higher EPS sheets and let it flow down into the ring beams. Don't pump the concrete directly into the ring beams. I don't believe Isoquick tends to have ring beams, so not an issue with their system.

Edited October 18, 2023 by IanR

[saveasteading]

1 hour ago, IanR said:

Talk to an experienced structural Engineer

I get funny looks talking to myself.

I'm asking questions not saying the system is no good.

It is all easy enough to understand, thanks.

 

I don't want to annoy you any more, and can see you are v defensive of the system. I'll say goodbye.

[Gone West]

15 hours ago, saveasteading said:

Was this a package contract for the whole slab to that stage? Ending up at 3x the cost, and the delay.

Yes, it was a package contract from laying the type1 to power floating the concrete. We knew we were the first Isoquick installation in the country and so were guinea pigs to a degree, although we did have company technicians on site. We paid a fixed price, and all the extra costs due to the cock ups were covered by the company, who didn't quibble. There was a couple of weeks delay.

 

15 hours ago, saveasteading said:

Concrete setting too quickly was presumably because they were taking too long to barrow it?

Yes, and the fact the concrete was coming from too far away in warm weather. It came down to a good system, being let down by poor UK concrete laying.

Edited October 19, 2023 by Gone West
grammar

[saveasteading]

1 hour ago, Gone West said:

the first Isoquick installation in the country 

Where does isoquick come from? 

From my travels I'm not sure concrete skills on small projects  are great anywhere.

[Gone West]

2 hours ago, saveasteading said:

Where does isoquick come from? 

The Isoquick technician who came to site was from Germany, so I guess it's German. The first time I heard of it, it was being used in Canada.

[gavztheouch]

I reckon there is a good business in pouring and finishing these slabs. I agree, most of the local insulated slabs near me have had errors, some big some just niggles. Usually it was sun contractors not giving a dam.

[saveasteading]

18 minutes ago, gavztheouch said:

reckon there is a good business in pouring and finishing these slabs

There are specialist companies who do only this. They are very good.

It's like the circus coming to town. Lots of kit, lots of workers who don't need instruction. I can't recall any quality issues with them at all.

I've stayed with them all day on several occasions, just in case.

It is also very hard work, and into the night when the concrete declines to harden.

Next day, they are off to the next job, leaving one worker to saw cut contraction joints.

 

The only problems are getting a date with a lot of notice, being ready for them, and cost. Also they aren't too keen on under 400m2 as this is a comfortable day's work.

 

We always put the buildings up first so that the slab was not rain or frost  affected.

[gavztheouch]

https://youtube.com/shorts/PecSnukpndw?si=CxSRduTSesWGMPF

 

 Probably a waste of time but I enjoy learning about these things. I built this self levelling ram that follows the rotary laser level. The idea would be to build a self levelling screed robot to level the final layer of stones under the isoquick.

 

it uses light sensors inside a 3D printer hood that’s painted black to stop light coming in from outside. This is clamped against the laser receivers led light panel to read the grade.

Edited November 22, 2023 by gavztheouch

[gavztheouch]

Just bought my rebar for the project. £3k worth of steel over 110m2 seems like overkill to me. 4 layers of 10mm mesh with 200mm grid spacing. 2 layers on top and two on the bottom.

 

 My current plan is to try and run the underfloor heating pipes between the top and bottom layers of mesh. At the end I’m thinking I can hook the pipe up and tie it to the underside of the mesh with a cable tie. The hard part will be routing the pipe between the mesh chairs that support the upper layers of mesh.