Building a stone wall sauna

[Anlaf Cununc]

Hey everyone, I have recently moved to the Inverness area and so far loving it up here despite getting bitten by midges every time I go out lol. The aim of this house was to live surrounded by the beautiful nature and be beside a loch. When I bought the property I realised the house came with a stone building that had fallen apart over the years and was used as a barbecue by the previous owners. Here are a couple of images of the building





And this is what it looks like now.









As you can see in the images, 2 walls are backed up against the soil and the left wall is open. My plan is to do pointing and lay the stones first on the left wall first and build it up to the desired height. Will be using lime mortar and will be pointing both the inside and the outside of the wall.

Now I have been told by a friend of mine that a building like this will take a long time to heat up if there is no insulation. I have no experience in building so all of this is being learned from youtube lol. Would like to get your ideas now on how to proceed. My original plan was to make the building look something like this from the outside



and have just bare stone wall on the inside. But now that I know it requires insulation I am not sure if I can keep the bare stone wall look on the inside. Please let me know what you guys think and if you have any tips on how to proceed it will be greatly appreciated. Thanks

[Grendel]

Insulation will obviously help . It can be placed on the outside of the stonework which will leave your interior bare stone. That will act as a heat sink although the sheer mass of it will take some heating up in the first place which means try to make it as compact as possible. What you are in effect creating is a sort of large pizza oven although I don't suppose you'll heat it by lighting a whopping great fire in the middle but the principal is the same.
Have you given any thought as to how you are proposing to heat this?

[Anlaf Cununc]

Insulation will obviously help . It can be placed on the outside of the stonework which will leave your interior bare stone. That will act as a heat sink although the sheer mass of it will take some heating up in the first place which means try to make it as compact as possible. What you are in effect creating is a sort of large pizza oven although I don't suppose you'll heat it by lighting a whopping great fire in the middle but the principal is the same.
Have you given any thought as to how you are proposing to heat this?

Well I am now clearing all the dirt and rocks that were packed up against the 2 walls and thinking of putting the insulation on the outside and cover it up with a thin stone wall on the outside. This way I get to keep the look of it all in stone. The work involved is huge so I am not 100% sure if the out side insulation will help or not?

The internal dimensions of the building are 7' x 7'. I will be getting a Wood Burning Stove like this one https://www.aqualinesaunas.co.uk/harvia ... ning-stove to heat it up. Can the moisture from the soil behind the wall actually creep in if walls weren't properly pointed on the outside?

[Anlaf Cununc]

Ignore my last message because I just realised that just underneath the top soil were these massive boulders stack up against the wall for support. So I wont be able to clear them out lol. My only option now is to make the inside like a normal wood cladded sauna. You can see the size of the boulders in this image.



I have ran into yet another issue now though lol. As I was clearing the soil from the left wall from the outside I noticed a lot of the stones were loose at the bottom so I started take them out as they had no weight on them whatsoever. This is what it looks like now







The stones are holding up ok at the moment with the mortar used in the past. But the mortar was not properly applied as most of them stones used at the base had no mortar on them. I will be using lime mortar to do the pointing and laying but can I use the mortar to make the base for the stones I will be placing under this area now? My plan is to stack some thin stones and pour a think layer of the mortar and the lay the stones on top of it. Is that the correct way to go about it do you think?

[Grendel]

Some years ago I worked on a job where some of the work was repairs to a bottle kiln. These are normally warm if not hot inside , unsurprising really as they are used to fire clay and glass products , and dry as well. However , when work ceased and the kiln cooled rainwater started to come in through the joints. Pointing it all up did cure it but the point is damp shouldn't really be a problem if it's hot.
Lime mortar will be fine and is better than cement for stonework if somewhat slower to work with.
With regards to heating how about a masonry heater?
https://en.m.wikipedia.org/wiki/Masonry_heater
I've seen some on tinterweb where the flue almost wraps around a room rather than just going straigth up and thus transferring more heat to the masonry .

[Grendel]

Forgot to add have the wood burner or fire fed from outside. That way the thing will work like the old roman hypercourses and you won't have to keep opening the door end it plus , importantly , there's no chance of the fume gases building up inside. Apologies if you have any thought of that but I thought it worth mentioning just in case.

[Anlaf Cununc]

Forgot to add have the wood burner or fire fed from outside. That way the thing will work like the old roman hypercourses and you won't have to keep opening the door end it plus , importantly , there's no chance of the fume gases building up inside. Apologies if you have any thought of that but I thought it worth mentioning just in case.

Thanks Grendel. So you are suggesting that I should make this wall into something like a masonry heater?



Sounds like a brilliant idea but I do not know how to make one though? Is there a manual or design concept I could read to make one? Are you suggesting I should take it all down and start from scratch and have the flue go around the whole building?

[Grendel]

Essentially the chimney passes through as much of the wall as possible to transfer as much heat as possible to that wall. Most of the ones I have seen on the internet are simple brick flues although there's really no reason you couldn't do it with a stainless liner ( obviously not the insulated type)
Years ago when it was still legal and ok to fit ones own wood burner I put one in my former house. The smoke went up a liner installed in the old chimney . I then infilled the resulting space with a sand cement mix . This made the wall into a heat sink which would keep the kitchen warm after the fire had gone out . Same principal.
Going back to the roman hypercourse idea , they worked by having the smoke and fumes from a fire drawn under the floor ( made of masonry pillars and tiles) and up through small chimneys in the walls all of which extracted heat in the process.
Up to a point it depends on how much of the original building you want to remain original or if you are prepared to take it all down and rebuild . The thicker the walls the better to act as a heat sink.

[Anlaf Cununc]

Essentially the chimney passes through as much of the wall as possible to transfer as much heat as possible to that wall. Most of the ones I have seen on the internet are simple brick flues although there's really no reason you couldn't do it with a stainless liner ( obviously not the insulated type)
Years ago when it was still legal and ok to fit ones own wood burner I put one in my former house. The smoke went up a liner installed in the old chimney . I then infilled the resulting space with a sand cement mix . This made the wall into a heat sink which would keep the kitchen warm after the fire had gone out . Same principal.
Going back to the roman hypercourse idea , they worked by having the smoke and fumes from a fire drawn under the floor ( made of masonry pillars and tiles) and up through small chimneys in the walls all of which extracted heat in the process.
Up to a point it depends on how much of the original building you want to remain original or if you are prepared to take it all down and rebuild . The thicker the walls the better to act as a heat sink.

Thanks Grendal. The flues I am thinking of creating will be entirely made out of stone as I have plenty of it on site. Do I really need to have the stainless liner? I am thinking of doing something like this image below for the entire building i.e. this pattern will be a long flue that use all the 4 walls.



The walls will be of the same thickness as they are now or maybe slightly thicker. Would it be ok to use lime mortar though? As the temperature will be really high inside the walls once the fire is lit. Also is there are a way to make the heat to focus toward the inside rather than the wall emanating the heat both inside and the outside of the wall equally?

[Grendel]

No you don't need a stainless liner . I only mentioned that if you weren't sure about brick or stone flues.
I'd certainly use lime mortar on the outside although for the harsher environment of the flue cement or even fire clay could be used . In terms of trying to "focus" the heat probably the simplest method would be to bury the structure as much as possible , soil being a natural insulator .

[Anlaf Cununc]

No you don't need a stainless liner . I only mentioned that if you weren't sure about brick or stone flues.
I'd certainly use lime mortar on the outside although for the harsher environment of the flue cement or even fire clay could be used . In terms of trying to "focus" the heat probably the simplest method would be to bury the structure as much as possible , soil being a natural insulator .

I will be putting a barrier behind the wall before I fill it with soil, and was wondering if one can buy a barrier that has a reflective side that can go up against the way to keep the heat focused in one direction. Also I am not sure where I can buy the stove that has a feed from the outside. Can you let me know how I can achieve that? I think I kind need to make a pizza oven first and then fit a door on both sides. But not sure where I can buy these doors?

[Grendel]

You could probably just use something like tin foil but I doubt it will have that much effect as you aren't reflecting any radiated heat , it's pretty much all heat transfer by conduction.
Some time ago a friend and myself made a portable bread oven for reenactment , essentially a pizza oven.. We started with a metal box and covered that in furnace lagging and a layer of sand cement render on the outside. There were loose bricks inside to act as a heat sink which also meant we could take them out to ove the thing. The metal box has warped but the insulation has done a pretty good job of keeping most of the heat inside although some still escapes through the sides. The principal will be the same with your sauna.
I don't think you need a stove as such , simply build the whole thing out of stone or brick and that way you can make it any shape or size you want.
Not quite sure about the doors , you won't need a door when it's burning as that's where the air will be entering and when t'ms not in use a simple wooden slab would suffice to stop anything crawling inside.

[Argyll]

An old work colleague of mine Alan Dunning moved up to Beauly a couple of years ago. He built a new house there. It's a beautiful part of the country.

[Anlaf Cununc]

You could probably just use something like tin foil but I doubt it will have that much effect as you aren't reflecting any radiated heat , it's pretty much all heat transfer by conduction.
Some time ago a friend and myself made a portable bread oven for reenactment , essentially a pizza oven.. We started with a metal box and covered that in furnace lagging and a layer of sand cement render on the outside. There were loose bricks inside to act as a heat sink which also meant we could take them out to ove the thing. The metal box has warped but the insulation has done a pretty good job of keeping most of the heat inside although some still escapes through the sides. The principal will be the same with your sauna.
I don't think you need a stove as such , simply build the whole thing out of stone or brick and that way you can make it any shape or size you want.
Not quite sure about the doors , you won't need a door when it's burning as that's where the air will be entering and when t'ms not in use a simple wooden slab would suffice to stop anything crawling inside.

I manage to find a guy on ebay makes these kinds of doors. I will be using them for front and back. I am still not sure why I can't use the lime mortar for the whole job? I am sure Romans used lime mortar for their baths constructed using the same principle? Is lime not heat resistant enough?

[Grendel]

There's no reason why you can't use lime for the whole thing , sorry if it came across as earning you can't. Any material will be effected by fire , the sand cement on our bread oven has crumbled over time around the opening edges where the flames lickout .
It's true the romans used lime mortars . They used various different mixes too and added other ingredients to give different properties . Volcanic ash for instance. On one job the instructions were to add brick dust to a lime mortar , the architect said it had a pozzalonic effect. We ended up looking that up and it referred to the town of Pozzula ( not sure of spelling) where the romans developed their concrete. Evidently the brick dust which is of course fired clay reacts with the mix to make it firmer and go off quicker . We were warned against adding small amounts of cement as in low proportions it eveidently weakened the mix.
One thing you could do is to test various mixes. Make up several samples ( different sands , proportions , lime or cement etc) and once dried put them in a fire to see how they fair. Also it probably wouldn't hurt to do the same with the mix for the exterior pointing to gauge colours .