Base for Pamments and stove inside Inglenook

[dans]

Morning all,

We're currently restoring an inglenook in my 17th C Farmhouse. I'm looking to put in a Wood Burner, which will sit on Pamments. My builders are suggesting a concrete base within the Inglenook, to add support to the large heavy Stove, but also to stop damp drawing up through the floor, which is currently just earth. We'll then bed the pamments in with a 7-2-1 (sharp, lime, cement) mix.

It's the words "concrete base" that I'm not keen on, but I don't mind the use of modern materials used in the right fashion. Obviously, a modern wood burner is not a traditional item, and will be much hotter than a 'tradition open fire'.

I just want to make sure we're doing the right thing, before anything becomes irreversible!

Your help, as always, appreciated!

Dan

 

[dans]

Here's a picture of the Inglenook in question. Be warned, it's work in progress!! It needed a fair amount of work and has had a lot of bad repairs over the years. Extensive use of coment, concrete, non-original lintel, bits of softwood wedges in gaps, lead, aspestos..... you name it!!!

 

[dans]

Compared to the Inglenook the other side, which is in GREAT condition, with a fabulous original Bresemer beam with detail...

 

[Flyfisher]

We have exactly the same sort of fireplace arrangement, together with a suspended wooden floor, all over bare earth. Presumably, your walls (like ours) have no DPC so what would your builders suggest to stop them also "drawing damp up"? (No, don't ask them!). In short, I wouldn't worry about it and not do anything to locally block any moisture that might exist and force it to accumulate somewhere else.

I'm also planning to install a woodburner on top of pamments, but I'm going to lay them on a limecrete base rather than concrete. The earth under our floor is bone dry to the touch but even if some damp does migrate up the walls and through the limecrete, it is soon going to be dispersed by the heat from the wood stove and normal ventilation.

Really, I can't see any reason for a concrete base, so why take the risk?

 

[dans]

Thanks Flyfisher.

That's exactly the question I did ask them. Sometimes it's difficult to argue as admittedly I know less than they do. Which is frustrating in itself! But a concrete base inside my old house, doesn't seem quite right...

Perhaps a concrete/lime mix would be a compromise...?

 

[DJH]

I'm not wishing to be provocative but I take every opportunity that arises to introduce some form of dpc whenever I can. What is so wrong in laying a firm concrete base in this particular situation with a dpc beneath it? Sometimes the argument that it's always been like it is counter productive. For example central heating, electricity, insulation etc was never in place in the past and, do we really believe that had some modern materials been available at the time of building that they wouldn't have used them?

I live in a very old farmhouse built on a mixture of clay and stones and in the one room that I didn't replace the existing floor with it's thin covering of concrete which doesn't have a dpc below and I'm now attempting to fix the damp problem retrospectively. I've lined the external walls throughout with foil backed insulated plasterboard following the contours of the walls without attempting to level them in any way vertically and re-introduced paneling at low level with vents fitted at floor level to allow for evaporation to be dispersed.

Fixing the plasterboard with broad headed plastic nail type fixings the original wall finishes are protected, apart from holes drilled for the fixings, so the integrity of the original is undisturbed and can easily be returned to as it was when I bought the place by simply removing the board. All services run behind the paneling and is easily accessible and I live in a nice warm cosy house which is sleeping behind it's internal covering of plaster board.

Doug

 

[Flyfisher]

I'm not wishing to be provocative but I take every opportunity that arises to introduce some form of dpc whenever I can. What is so wrong in laying a firm concrete base in this particular situation with a dpc beneath it? Sometimes the argument that it's always been like it is counter productive. For example central heating, electricity, insulation etc was never in place in the past and, do we really believe that had some modern materials been available at the time of building that they wouldn't have used them?

That's a fair question Doug, and I entirely agree that had modern materials been available a few hundred years ago then they would have definitely been used. But I think the issue is how they would have been used.

There's clearly nothing wrong with concrete, cement mortar and DPC membranes in modern houses because they are designed from scratch to be impervious to damp and everything works well. However, a house built without such things will generally rely on its breatheability to allow the inevitable damp to freely dissipate. In such cases, the addition of modern materials can change the behaviour of the building in ways not originally intended and, sometimes, cause problems - maybe minor, maybe major.

In dans case, an impermeable concrete fireplace slab is certainly not consistent with anything that has gone before and making that area of the floor completely impermeable might, depending on the ground conditions, cause moisture to accumulate under the dpc/concrete and lead to its migration to the surrounding wall, thus making them wetter than they would normally be. It may be the case that the walls can dissipate the extra moisture without problems but it may not - I don't think anyone can be really sure. Only time will tell. In such cases, why take the risk?

Perhaps we should consider things from the other end of the stick? What's the risk of using limecrete?

Perhaps a concrete/lime mix would be a compromise...?

Yes, it would be a compromise - but to what end?

Tell you what, you go with concrete, I'll go with limecrete and we can compare notes in a few years :wink:

 

[DJH]

I think that keeping houses as they were when built on the assumption that lime mortar was used so that walls could breath is a fallacy. Lime mortar was all that was to hand for building and wide walls used simply on the assumption that they were more likely to stay up. Some attempts were made to prevent damp such as the inclusion of slate courses and rubble filled walls but, on the whole, dampness was something put up with because there was no solution to the problem available at the time.

There were of course jerry builders back then where no thought or consideration at all was given to dampness in building structures but I still fail to see why it should be acceptable, with moderns materials available to us, not to make use of them. I also can't quite grasp why it's suggested that heat or warmth inside a house will help walls to breathe. I suggest that damp problems are exacerbated by modern internal heating temperatures coming into contact with cold damp walls giving rise to condensation rather than or along with breathability. What could be wrong with a wall if damp could be prevented from affecting living conditions by having some sort of dpc or insulation on one side and being able to breathe from the other outside skin?

I can see no reason why a dpc couldn't be used to advantage in this situation of Dan's as the actual area is not large and if there was that much moisture in the floor then I would definitely investigate where it was coming from and try to remedy it. If in fact there is not much moisture in the floor then what other reason could there be for not using a dpc and maybe some insulation to reduce the risk of condensation as this floor would be very cold and the wood burner above it would, using the breathability argument, be damp all the time apart from when the stove is going full tilt.

Just some thoughts!

Doug

Later. Reading back over this it would appear that I'm some sort of philistine modernist who doesn't care for old properties. Far from it. I'm a proponent of all old trades and methods, as some of you might have gathered by now, it's just that I don't see why we can't take advantage of both what we now know and what we have to hand to help solve our problems. An example might be that I can work with lead pipes but at the same time I just love the new plastic pipes to work with.

 

[MdB]

My view on whether or not to fit a DPC is that it depends...

If you can fit a good DPC all the way through the building then do so as it is the best solution. The more problematic question is whether or not to fit a partial DPC? - often in the floor only and not the walls.

Thirty or forty years ago, the previous owner of our property decided that the concrete floor was damp and basically laid a DPM over the top and then poured another 50mm of concrete. This certainly gave a dry floor but it also would have reduced the amount of moisture evaporating from the original floor and it was very damp underneath when we lifted the lot. The ground being damp, there being no DPC in the walls and because the previous owner was a numpty and didn't remove the plaster at the bottom of the wall before laying the new concrete, we ended up with rising damp all the way around the bottom of the walls. I would therefore say that fitting a partial DPC/DPM is something that will fix one problem but may cause issues elsewhere.

Our solution was to relay the floor (with DPM) and rebuild the walls (with DPC) which was a bit drastic but something we needed to do. I then had the question of what to do with the old walls (about 20%) which we certainly weren't going to replace. I ended up using limecrete for a strip approx 300mm wide next to the old wall - which to be honest I don't think helped a lot - and more importantly lowered the ground levels externally. For our stove, I installed a big granite slab into the fireplace which isn't going to let any moisture through anyway. I used NHL underneath it rather than cement but I don't really think it mattered.

 

[Flyfisher]

I'd agree that inserting a dpc underneath and entire old building would be fine, but it's not an easy job ( perhaps Zebra can confirm the work involved as I believe she recently did just that).

Only inserting a dpc underneath new floor slabs would be the equivalent of cutting holes for the walls in a new build - why would anyone want to do that? Isn't it bound to cause problems?

I take Doug's point that lime mortar probably wasn,t used historically because of its breathability but only because OPC was not available, so perhaps it was a happy accident, but the fact remains that there have been countless numbers of old timber frame houses that have survived for centuries until rendered in cement mortar which has subsequently trapped moisture around the timbers and caused serious damage.

I wouldn't consider any materials 'good' or 'bad' as such, the important thing is to use them appropriately.

 

[Zebra]

My builders are suggesting a concrete base within the Inglenook, to add support to the large heavy Stove, but also to stop damp drawing up through the floor, which is currently just earth. We'll then bed the pamments in with a 7-2-1 (sharp, lime, cement) mix.

Without wishing to be disparaging about your builders, builders do tend perhaps to think of using concrete as a matter of course, it's what comes naturally to modern builders, and the materials are freely available.
How bad do you think the damp situation is? Could you, as an experiment, lay down a sheet of polythene inside the fireplace, weighted down, or a rubber car mat, and leave it for a while, then lift it and see if it's damp underneath?
I did indeed cut in a dpc all the way round the old part of the house (lots of work but achievable because mine is a small house), and installed a concrete insulated floor with dpm underneath BUT.... the fireplace has neither. For a number of reasons: I had already laid a new slate hearth on top of the old uninsulated concrete slab and installed a woodburner a year previously; the walls at the base of the chimney are 18" rather than 9" like the walls of the house so it would be very difficult to do; there is a bread oven on the side of the fireplace which I was loathe to disturb; there was never really a damp problem in the fireplace anyway after removing the cement render from the walls.
Installing the dpm in the house, and the dpc in the walls of the house has not made the damp in the fireplace worse. I get a TINY patch at the back sometimes after very wet weather.
Is any of this useful? I'm not sure I'm really answering your question. As it's not a huge area you'd be covering in concrete, I'm not sure it would have a very big effect on the damp elsewhere. I think it has to be considered in the context of what arrangements exist elsewhere in the room, how bad the damp situation is, and what your plans are for the rest of the room - both floor and walls.

 

[88v8]

How bad do you think the damp situation is? Could you, as an experiment, lay down a sheet of polythene inside the fireplace, weighted down, or a rubber car mat, and leave it for a while, then lift it and see if it's damp underneath?

Yes. See if there's actually a problem, it may be perfectly dry.

I am also against local DPMs - although.... pamments and stone slabs don't exactly breath anyway, most of the breathing is through the joints, and in your fireplace there won't be that many joints so does it really matter - but leaving that aside.... the woodburner will probably weigh a couple of hundred pounds, on four legs, so that's 50lb a leg. If you can stand on the fireplace in your stillettos, so can the woodburner. A couple of inches of limecrete, bed and point the pamments in lime and leave it at that.

Ivor

 

[Penners]

I echo FF's point-of-view. If you're going to be pouring a constructional hearth for the fireplace anyway, I don't see that there's anything to be lost in using limecrete and possibly a fair bit to be gained.

My only additional thought is that, if it were me, I think I would drop a bit of reinforcement mesh into the wet material as an insurance policy against cracking. I don't think there's a high risk of this, but for the sake of a few pounds it seems worthwhile to be belt=and-braces about it.

FF - do you know whether stainless steel is advisable in limecrete? I've never used the stuff myself.

 

[DJH]

Penners, stainless steely wheely rods are fine with any materials we are likely to come across although, in marine conditions, austenetic or 316 grade should be used. A simple test for 316 is to touch it with a magnet, if it's 316 it won't be attracted to it.

Doug

 

[Penners]

That's a coincidence. I used to know a girl who lived at number 316. I wasn't attracted to her, either.

But no doubt the feeling was mutual.

 

[DJH]

Hmm. They're all attracted to me Penners and both poles!!! :lol:

 

[Penners]

Sadly, I don't know any Poles.

 

[dans]

Thanks everyone.

The soil is dry. The very back bricks on the fireplace were crumbly, prob caused by damp, but prob a long time ago, or maybe due to the fireplace being completely closed off by cement for the past 50+ years, who knows??

I think a cement base and the pamments bedded in with lime is probably going to be okay, given I have no obvious damp issues in the soil... I'm probably being over-paranoid at times, but I want the job done properly, and I certainly don't want to revisit areas in years to come...

Limecrete's an option but would take ages to dry??

 

[Flyfisher]

Weeeelllll, I'm no expert but I'd expect the soil to feel dry because it is exposed to the air and any moisture will be freely evaporating. I'd also expect the skin on your hand to feel dry but try wearing a (dry) rubber glove for half an hour . . . .

As for limecrete, my understanding is that it will set solid pretty quickly but will continue to 'cure' (carbonate) over many weeks (maybe months, I don't really know). I would expect it to be solid enough to walk on after a day or two. Although the chemistry is different, the same sort of thing happens with concrete and I understand its rated strength is only reached after at least a month, even though it can be walked upon after a day or two.

 

[Flyfisher]

My only additional thought is that, if it were me, I think I would drop a bit of reinforcement mesh into the wet material as an insurance policy against cracking. I don't think there's a high risk of this, but for the sake of a few pounds it seems worthwhile to be belt=and-braces about it.

FF - do you know whether stainless steel is advisable in limecrete? I've never used the stuff myself.

I''ve read that ordinary steel reinforcement is not advised in limecrete, though I've not found anything definitive. I don't know if this is because of lime corrosion or simply the increased risk of rusting because of the permeability of the lime. I'd guess stainless steel would be OK, but it would be a guess and I'd be checking with some real limecrete experts if it was for me.

Having said all that, is it really likely to crack. With a good compacted hardcore ground preparation and a 6-9 inch slab thickness (as I'm planning to do), I wouldn't be too concerned about cracking, especially as the slab is bounded on three sides.

All amateur musings though, so I could be wrong - but I'll be able to report on my own fireplace experience later in the year.