Debate open to all-comers to see what happens ... observations, experiences and thread links welcome.
Issues: Ecology, Cost, heat store behaviour, compatability with wet & dry UFH, behaviour at installation etc etc ...
Thanks,
Mike.

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1554&page=1

covers a large slice of the arguments

Having read the protracted pimg-pong match referred to above (http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1554&page=1)
I'm still undecided from a CO2/emissions etc point of view, but in the mean time would like to pick out one technical point which may make my decision for me in the end ...

"The main advantage of cement [used on its own] over lime is its 'setting time' It gains most of its strength very quickly - Partial set within 6hrs, quite hard within 24hrs Very hard within 30 days. Lime however can take a very long time to gain even partial strength, meaning the job often needs to be spread over a much longer period of time."

My original question was about "OPC" vs Lime in relatively large floor slabs as opposed to as a mortar.
I had heard that Limecrete "makes a better heat store" but was not clear in what way this could be the case.
I had also heard that the setting &/or curing properties of limecrete make cracking more likely in a thick slab, but also make cracking less likely in a thin-film situation like layers of mortared bricks.

My ground heat store is beginning to look like it will have sections made in different ways as a test bed for comparing methods, as there doesn't seem to be any other way of "proving" comparative efficiency.

One section will be constructed with reclaimed bricks from on-site interleaved with insulation in such a way as to force a long path for heat to reach the top of the floor slab, thereby creating a time lag sufficient to set up an interseasonal store ...
The heat for this section will be delivered by fluid in copper pipe, and the pipe will be run in the mortared planes between the layers of brick that make up the storing strata (as opposed to the insulation/diversion strata).

My intuitive take on this is that a lime based medium would be better suited to running the pipes as it seems less likely than OPC to develop cracking in this thin-film situation (as opposed to being more likely in a thick slab) ... and if limecrete is indeed a better heat store maybe it would be a better conductor of heat from the pipes to the bricks?

As ever any observations welcome .....

Ta!

Has the house been live in?

The thing that you could be missing is that heat or warmth drives away moisture, most houses are bone dry under the floors, I have taken loads up and understand why this is.

Insulating the floor will make it slightly cooler under there and that in itself could make it damper, just something to beware of.

I would spend on insulation, I always preferred to lay insulation under the concrete, then all the thermal inertia material is inside the thermal envelope which gives additional comfort.

Will the walls be insulated? And how will the insulation join the floor insulation.

House has not been lived in for nearly 18 month now, and when it was I rarely had the heating on as was too expensive to run! Had a lot of rain this winter so was pleasantly surprised how dry it was under the concrete which was laid directly on top of clay with a lot of voids for moisture to potentially collect in.

I've just spoken to a good local concrete firm we have used for farm work and they also suggested I can prob get away without a concrete slab foundation and just level off the clay with some sand to protect the DPM then put the solid insulation directly on this with the UFH and 75mm screed on top. Benefit of this means less digging and a thicker layer of insulation possible.

As recommended on some other threads http://www.secondsandco.co.uk/ have some 130mm thick PIR board. It doesn't have any foil backing but works out cheaper than EPS so I'm considering using this with either 25mm or 50mm layer of foil backed PIR on top as will hopefully work out cheaper than buying all new board and be more effective. Any thoughts on this or experience of what quality the second hand boards from this company are like??

Current plan is to plaster the walls level with lime then insulate internally with cork boarding from Ty Mawr. The boards will go down the edges of the UFH slab to meet the underfloor insulation. I'm hoping because the lime and cork is breathable what little moisture there is under the floor will wick up the walls and escape either through the cork boards or into the cavity of the stone wall. Cannot do EWI as in a conservation area.

The lime will take forever to dry and cork boards are more expensive than dry lining with PIR but I don't think I can take the risk of trapping moisture in the walls as the wooden window and door lintels will all rot. However I might cheat a bit and dry line some of the walls which don't have timber in them and are at lower risk of rain penetration, depends how much money I have left in a few months time I guess!

I would want to see 100 structure so minimum without regs would be 100 concerted power floated with pipes and grid

Thanks for that Tony, a thicker screed makes sense to me. However by grid do you mean the screed should have steel mesh reinforcing which the UFH is attached to, I was just going to staple the UFH pipe direct to the insulation? The screed I'm thinking of using is not self leveling but a readymixed mortar with fibre in it, which from memory I think should replicate the strength of A142 steel mesh.

I wasn't too concerned about the structural strength of having a slab considering what I have just dug up was done by my grandparents in the 1960's and was between 30mm - 100mm. They just poured it against the skirting boards which have long since rotten away thus providing no structural support. On the plus side it was nice and easy to dig up!

I would use a reinforcing or anti cracking mesh, do you need
to pass building regs?

I'm in a similar situation and only have around 30 cm depth to play with. I also have the added complication of potential lateral water penetration due to being in a flood zone. The base is a heavy, firm clay. My plan is simply to fill with glass foam aggregate, 20 cm, and compact this with a wacker plate, then 10 cm limecrete screed finish on top. Geo textile membrane under the foam glass to keep it clean and under the limecrete. No DPM's. I wrote on here before because I was curious about why there cannot be a pourable limecrete, i.e. adding a plasticizer to the mix to make it flow, which could be done at the cement works? And/or simply making a runny mix, lower compressive strength, but surely enough for a domestic floor and more water in mix = increased permeability, which is the raison d'etre for using limecrete? Additionally I'm curious about using crushed limestone aggregate in the mix, Seems crushed limestone will increase the insulation of the limecrete ( see "liquid limestone" in Australia ), any one have experience with this?

I'm nearly there now.. so in a few weeks I will go to the cement works here in Germany and ask them what they can do, if not then I have the same dilema, either mixing limecrete by hand, extra time, expense, effort. Or copping out and going for a concrete slab. p.s. There is an architect here in Germany, specifying just compacted foam glass with clay tiles on top... as a breathable, insulated and flood proof floor. But I still like the idea of having a floor slab/screed of some sort..

i put 200mm graphite eps under 100mm reinforced concrete slab in an old farmhouse where I was initially considering a breathable build up. No problems after 2 years around the external walls. I have wood fibre insulation on the inside of all external walls and MVHR and pretty airtight as well which all helps.

I'm happy I did - certainly cheaper than the limecrete method.

I have no doubt a limecrete slab and the glass pumice insulation are the best option for a house with damp problems and no DPM membranes in the walls. However they are far more expensive in terms of both materials and labour to hand mix than bog standard EPS and ready mixed screed. In my case I have decided to go for the cheaper option whilst also increasing the insulation thickness under the slab to reduce running costs long term. Limecrete both needs to dry out, which only takes a few days as you point out Pile, however just like OPC but slower it also needs to cure which is a chemical reaction with air, a process that never stops so ideally needs to be left exposed for as long as possible before laying floor coverings etc.

Silky - there are companies who can deliver ready mixed limecrete or mix the amount you need on site but when I got quotes they were way out of my league. I highly doubt you can get a free flowing limecrete, I would guess any plasticizer would seriously compromise the breathability and so there would be no benefit over using much cheaper OPC products. Adding excess water to make it flow would also make the limecrete so weak your floor covering would likely fail, or cracking could damage the UFH pipework?

Anything with air voids in it will insulate, crushed limestone as far as I know is a solid material so no insulating properties whatsoever? My house has 70cm thick solid stone walls, however from an insulation point of view they are useless!

I think the foamed glass does compact down very hard but I wouldn't risk laying UFH without a decent solid screed which won't crack. Maybe a good idea if not laying UFH though.

Tony - I am not being inspected for building regs but am trying to make sure I surpass them especially regards insulation. With the floor I know in theory I should put in a layer of hardcore and a strong slab to meet the regs. However we have laid hundreds of square metres of concrete in the farm buildings, only 15cm thick C30 slab with fibre, laid directly on the clay with no DPM or steel mesh in most of it. It gets hammered by 10 tonne plus tractors driving over it all day but as the clay is so hard we have had no problems with cracking or water coming through. However good drainage around the building is critical to make sure water doesn't get in and weaken the clay.

As my house has lean to buildings on three sides and the ground level on the 4th side is below the new floor I am confident I can keep water out so no point digging deeper just to put in hardcore. Apparently its harder to staple UFH direct to EPS compaired to PIR so will prob cable tie it to A142 steel mesh where needed as we have some spare lying around anyway. Despite building regs it should be bomb proof by the time we are finished!

Thanks for your thoughts everyone :)

We are also fitting MVHR as convinced this will transform the air quality in the house and eliminate damp.

Thanks jfb thats a big help. I was thinking about using cork boards from Ty Mawr but may go down your route depending on what works out as the most cost effective method. I will make the house as air tight as possible within budget, its one of the benefits of doing the work myself.

This is probably a rooky question but did you do your first fix wiring and plumbing before applying the render under the IWI or afterwards? My electrician suggested I should plaster the walls level first and then he will know where the finished wall surface will be so he can fit socket boxes etc before the IWI layer goes on. This would mean we would have to notch out the cable runs in the IWI, to me it makes more sense to bury the wiring in the base coat plaster so we have a flat surface to stick the IWI to and fit socket boxes after? Will obviously cut out holes for electrics in IWI before fitting, assuming the other half doesn't change her mind about where she wants them!

Posted By: torrent99Are you using thicker cable to take into account that it's going through Xmm of insulation on it's way to the socket box?

The part that is against (or in) the wall is on an uninsulated surface, so is fine. The part that goes through the depth of the insulation isn't long enough to have to be derated.