Floor bricks, pamments and underfloor heating

[AMc]

I have 'reclaimed' the floor bricks and pamment tiles from our vinery, old kitchen, old bathroom and storage cupboards which we're relaying over a new concrete* floor slab and insulation. I have a concrete screed going over wet underfloor heating.

Originally the bricks and pamments were laid on weak dry mix of lime and sand and most came up easily. I'm keen to make it possible to remove, relay or reverse what we can in the future so I'd like lay them the same way. I also want to keep the joints between the bricks as small as possible so the floor looks as close as possible to the original floors. I'm not able to get a clear answer about how laying the floor this way may affect the heating efficiency.

What should I lay the floor bricks on?

* I know it's heresy, let me explain. The building is 3m wide - as I'm not listed to meet building regs I would need >300mm of sheeps wool (or similar) on each wall (room shrinks to 2.4m wide). Upstairs >300mm of sheeps wool would have pushed the roof up by more than a foot (as the head height is restricted). Then there is the vinery to complicate the thermal calcs.
Once I was forced to use Ecotherm solid boards, breathability became impossible - having a breathable floor and non-breathable walls and roof seemed like madness, so we've dry lined the and are leaving the walls with no chemical DPM. Sorry

 

[AMc]

Well Googling away on floorbricks and underfloor I came across a PDF of a H&R case study - and I actually have the magazine in the office.

"Next, Paula and Barry removed the clay floor bricks in the kitchen, which had been attached to a cement screed. They were able to save enough of them to lay them in sand on top of the underfloor heating in the rear extension.".
As is often the case with H&R case studies this isn't quite enough information
Did they use just sharp or just soft sand?
Did they add any lime in the mix?
Did they seal the surface against spills, beeswax?

I've emailed one of the owners to see if there are more details - her site http://www.paulasunshine.co.uk/ - she's written a couple of books about restoration so hopefully there will be a response.

 

[Schoolmarm]

Isn't she a member on here already?

 

[AMc]

I don't know? I was kind of fishing with my post No sign of that name in the members list, but then I'm not really called "AMc" by most people.

 

[Schoolmarm]

I know, I looked but I vaguely remember her being here, hmmmmmmmmmm.

 

[AMc]

Well member or not I got a quick friendly response, the crux of which was...

We just laid the underfloor heating pipes on top of the screed and polystyrene and then laid sharp sand (no cement or lime - not necessary) on top of the pipes and the bricks butted up tight (no mortar at all) on top of that. You have to have good bricks (straight sided) to get everything fitting tight. If you want to afterwards you can brush a dry mix of silver sand and hydrated lime powder into the cracks then spray water over the floor to solidify. But this does make the bricks very white unless you scrub them. We don't seal our brick floors as the sealant (beeswax or linseed oil) attracts, and holds on to dirt worse than unsealed bricks. I just mop it over now and again and once a year get on my hands and knees and give it a damn good scrub (Victorian style). Hope this helps. Regards Paula

It's so nice when someone you don't know does something so helpful!

 

[MdB]

We just laid the underfloor heating pipes on top of the screed and polystyrene and then laid sharp sand (no cement or lime - not necessary) on top of the pipes ...

I'm not an expert in this but I wouldn't have thought sand by itself was good enough on top of the underfloor pipes. You want good heat transfer and the air in the sand would act as an insulator. If you don't get enough transfer, the return water temperature gets too high and you can start short cycling your boiler which makes it inefficient.

 

[Flyfisher]

On the few occasions that I've had CH pipes laid within a solid floor the plumber has sheathed the pipes in a felt-like material, explaining that this allows the pipes to move as they heat up and cool down and not 'grate' against the floor substrate, which could lead to leaks. It also insulates the pipes, although that's not the primary reason, apparently. This was with copper pipes.

Clearly, underfloor heating is a different application and insulated pipework would be counter-productive. Direct contact with the floor material is therefore a good thing, but what prevents the pipes from chafing as they heat up and cool down? Is the pipework specially designed to prevent this?

Having once experienced a collapsed ceiling because of a leak resulting from two copper pipes just resting on each other, I'm now more mindful about how pipes can be damaged through tiny movements over time.

 

[AMc]

Hmmmm well the air in the sand acting as insulation is my primary worry. My pipes will be encased in a cement screed. They're plastic (Ivarpex Barrier Pipe it says here), specifically designed for this application so that must be OK - changing that would invalidate the guaranty on the heating anyway so its non-negotiable.

I'm hoping that I can bed the bricks on a thin bed of sharp sand on top of the screed. At least if it doesn't work it would be possible to lift and relay the floor - trying the cement route first would obviously make that impossible.

Any other thoughts are still very welcome...

 

[JoceAndChris]

Interesting reading.

I hope you find lots of answers.

 

[Flyfisher]

I'm thinking aloud here (a novelty really, aloud or otherwise) but if insulation reduces the conduction of heat, i.e. rate of heat transfer over time, won't that mean that the underfloor heating just takes longer to get up to the internal water temp, which might not be a problem given my understanding that it's designed to be on more or less constantly anyway.

If the "insulation" on top of the floor, i.e. the air within the house itself plus the structure of the house, is greater than the "insulation" of the air within the sand around the pipes then, eventually, the floor must get up to full heat because it can't lose heat to the house quicker than the underfloor water can lose heat from the pipes/sand/bricks of the floor. But if the house is badly insulated and very draughty then the underfloor system will not be able to transfer heat to the house quicker than the house is losing it. If you see what I mean (and if you do, let me know because I'm not entirely sure I do!).

 

[MdB]

Flyfisher you are correct (I think) but I think you are missing the fact that the boiler / heat source will have a constant heat output. If the heat conductivity is poor, this means that the temperature of the water in the pipes will rise until the heat radiated from the floor reaches the same as a good heat conductivity floor. i.e. the temperature in the room will be exactly the same in both cases, the only difference will be the temperature of the water in the pipes.

The problem comes in that if the temperature of the returned water gets too hot, the boiler / heat source will switch off (called short cycling). Our heat pump hit this problem when first installed and we had to tweak the settings to allow it to run at a higher temperature (which is less efficient).

 

[Flyfisher]

Yes, right that I didn't consider the boiler. So, with too much insulation (= too little conductivity) in the underfloor pipework and flooring there will be a limit to how quickly the heat source can 'lose' it's own heat into the circulating water. I can understand high output devices such as boilers having problems with this, but I thought that heat pumps were ideal for such conditions, i.e. constant source of 'low' heat rather than the short but high-output bursts from, say, a gas boiler. Presumably low-tariff (overnight) electricity might also be a suitable source for such a system.

I guess this all shows how important it is to have a well-balanced system for best efficiency.

 

[MdB]

I might have remembered these figures wrong but I think they are about right:

Room Temp: 19 deg C
Heat pump out: 40 deg C
Heat pump return: 30 deg C

The limit to the return temp was set at 30 deg C so the heat pump was short cycling (switching on and off). I increased the limit to 35 deg C and everything was fine.

 

[robgil]

a plumber should sheath any copper pipe that he/she lays in cement/screed etc as the cement/screed or whatever will eventually cause the copper to corrode.
ive seen some people lay 15mm plastic pipe inside 22mm plastic pipe in places as added protection.

 

[AMc]

Agreed about the copper pipe - the water feeds to the downstairs loo and kitchen sink, cooker supply line etc were sheathed in pipe insulation covered by DPM which in turn is covered under ecotherm board insulation, with with the underfloor heat pipes stapled and clipped to the insulation. There are no points where copper and concrete could meet. According to the underfloor heating guys practically everything including flux corrodes copper pipe if you're not careful.

We're still trying to work out the best bed for the floor bricks over the screed. Currently we're favouring a weak lime/sand mix...
The screed is going down this afternoon so I have a couple more days to faff before I must make a decision and stick to it.

 

[AMc]

Well to update you, we settled on a 6:1 mix of sharp sand to lime which seems to be working out OK. I can't finish the floor until we get the well cover installed (!) but most of it's down and looks good. They even fitted the woodburner yesterday and delivered the internal bits of the heat pump and hot water cylinder.

Now I need to protect the pamments in the vinery and the floorbricks in the future kitchen. I'm using Osmo Polyx (hardwax oil)[/url]on the bathroom floor upstairs and it says (on the tin) it's suitable for unglazed ceramic tiles. I have a couple of offcut bricks and pamments drying.

Is there any good reason not to use this or any alternatives (e.g. beeswax) I should be testing?

Osmo Polyx lnks
http://www.vanillawoodfloors.co.uk/index.php?cPath=24_79
http://www.osmo.de/gb/products/color/holz_im_innenbereich/hartwachsoel.php

 

[Hatster]

Maybe a daft question, but why do the pammets and the floor bricks need to be protected? I don't think ours are?

 

[AMc]

Most of the floor bricks and pamments been under concrete screeds for >40 years. Pulling the concrete off, lifting them up and pressure washing off the bitumen etc. has removed any build up of wax etc. that would normally protect them from grease, wear and our favourite - spilled red wine. They're more or less a new surface and I want to prevent them from becoming stained.

Polyx is basically a mixture of waxes and oils dissolved in white spirit to make it easy to apply. The testers are on their second coat and look good. I'm just interested if there are any real gottchas or a better finish.

 

[AMc]

(continuing to talk to myself )

I've put 2 coats of Polyx on the vinery floor, then spent a miserable 2 hot days brushing, pressing, shoving and cursing kiln dried silver sand mixed with lime (maybe 7:1) into the gaps between the pamments. After a couple of days I started to brush, then dry mop, then wet mop up the surplus. Apart from a few small holes appearing around a couple that aren't perfectly bedded in this is working OK. I've mopped 5 times and when wet the floor looks great but as it dries it dusts again. Hoovering rips the mix from between the gaps.

Is there anything else to do but keep mopping and mopping and mopping?