Grendel wrote: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 .
Ok so I am looking to order these. Please let me know if all of these are ok?
The fire resistant mortar isn't one I've come across . All the stuff I've used in the past was the ready mixed stuff that comes in large tubs. That's mainly because my father was a furnace controller and had access to the stuff for free. When we built our oven a friend brought some from a supplier and that too was the ready mixed stuff. That said I don't see why the stuff you've linked to shouldn't be ok.
The hydraulic lime will be fine. I've used it in the past and it's easy enough to work with. The masons I worked with mainly used lime putty but for your really quite thick walls the hydraulic is probably a better bet.
The sand is the one thing I would say to change. Building sand is generally a softer sand and lime work normally uses a sharper sand. The softest sand that was used was a yellow mercaston and even that was rarely used as the only sand in a mix. Colour for pointing mixes was quite important and I've seen concrete sand dried and sieved to use the finer grains. The internal mix was usually dubbed rough stuff where colour was not important but was still a sharp sand lime mix. Some sand is sold as plastering sand which is sharp and would be ok for your needs.
Was thinking of using the fire resistant mortar for just the fire place to be honest. Not sure if I need to use it for flues too? Flues wont be dealing with the fire but will certainly get hot, not sure if lime could withstand such heat?
To be honest both would be ok . The plastering sand probably has smaller aggregates which might make it better for the pointing although I have seen quite coarse sands for that job . It can depend on whether there's anything to match up with more than anything else.
I'd be inclined to use fire resistant mortar around the fire area but further away the lime should do the job. It may d pend on the joint thickness . Thinner joints I'd be happy with lime mix but wider joints , perhaps because of irregular stones , may very well be more vulnerable to heat damage so perhaps as a " belt and braces" approach use the fire resistant stuff as far into the flue as possible?
Grendel wrote:To be honest both would be ok . The plastering sand probably has smaller aggregates which might make it better for the pointing although I have seen quite coarse sands for that job . It can depend on whether there's anything to match up with more than anything else.
I'd be inclined to use fire resistant mortar around the fire area but further away the lime should do the job. It may d pend on the joint thickness . Thinner joints I'd be happy with lime mix but wider joints , perhaps because of irregular stones , may very well be more vulnerable to heat damage so perhaps as a " belt and braces" approach use the fire resistant stuff as far into the flue as possible?
Spoke to a couple of people at Masonry Heater Association http://www.mha-net.org/ today Grendel. They did say making a masonry heater wont cut it for me to make it into a sauna. They said the time to heat the whole 6ft x 6ft room will take a lot of time and it won't be able to keep the heat in for longer. I guess I will have to drop the idea and go with a simple insulation and wood cladding on the inside and a have a stove inside.
Now I just want to know if I can make a stove out of stones and use that as a heater inside? Wood fire saunas heat up the stones to get the heat so can a stove made out of stones serve as a better heater than a metal stove?
Well I never said it would be quick to heat or for that matter particularly effficient but if the romans could do it...
I think the secret is to keep it fired as often and for as long as possible , the romans probably kept theirs going pretty much continuously . With the oven we made the problem was in getting it to lose heat. Fired and left it stayed hot for quite a time , on shows the loose bricks were removed and spread about to speed up the cooling.
Grendel wrote:Well I never said it would be quick to heat or for that matter particularly effficient but if the romans could do it...
I think the secret is to keep it fired as often and for as long as possible , the romans probably kept theirs going pretty much continuously . With the oven we made the problem was in getting it to lose heat. Fired and left it stayed hot for quite a time , on shows the loose bricks were removed and spread about to speed up the cooling.
Keeping it running all the time would be going against the principle I guess. The thing is a lot of these saunas have a metal stove that is covered with stones which emanates the heat. Stones have high thermal conductivity compared to fire bricks though? Granite seems to be really good too and that is what I have lying about the site. What do you think?
Should work . I suppose the romans could keep theirs fired all the time because they were communal and used by many people so one for more personal use is always going to have some sort of compromise. Might be worth putting the stones in a fire just to see how they fair. Granite should be fine but some stones are less resilient. I remember one incident although it involved bricks rather than stone where we used some blue bricks of some sort and they started to splinter and shoot out little shards.
Grendel wrote:Should work . I suppose the romans could keep theirs fired all the time because they were communal and used by many people so one for more personal use is always going to have some sort of compromise. Might be worth putting the stones in a fire just to see how they fair. Granite should be fine but some stones are less resilient. I remember one incident although it involved bricks rather than stone where we used some blue bricks of some sort and they started to splinter and shoot out little shards.
I have heard of exploding granite exploding too. Also fire resistant mortar that I will be using might take up a lot of heat. Check this guy out though the fire place in his folly is made out of stone and I believe would have been very warm given the size of the room. https://www.youtube.com/watch?v=0i5DkqfrY3s
Nice video.
It seems almost a shame that it looks like you will have to abandon the idea of a stone sauna although I suppose you could clad your insulated wooden box with it . Should look a bit more in keeping with the landscape than what is in effect a shed. Having the stove inside will certainly work although for me a downside would be mess. In my experience dust always makes its way out of any stove and of course they require frequent emptying off ashes etc and it would seem a dirty sauna is , to me at least , counter productive.
Another bit of information which may be of use is a little experiment we did with our bread oven regarding fuel. We have used faggots , bundles of sticks and twigs rarely thicker than your little finger and they burn hot and quick with not a huge amount of ash. Good way to use up what would otherwise be rubbish. We tried larger pieces of wood and that didn't work anywhere near as well and didn't adequately heat the oven. There was a ruling in London ( 14th or 15th century I think) banning the use of straw so of course we tried that too. Works , just about , but it involves a constant feeding in of a small handful every few seconds or else it just doesen't burn. The same applied for chipping om a planing machine although hand shavings work well. However , both the shavings and the straw are messy to use and the floor got covered in bits so perhaps not the safest idea.
Grendel wrote:Nice video.
It seems almost a shame that it looks like you will have to abandon the idea of a stone sauna although I suppose you could clad your insulated wooden box with it . Should look a bit more in keeping with the landscape than what is in effect a shed. Having the stove inside will certainly work although for me a downside would be mess. In my experience dust always makes its way out of any stove and of course they require frequent emptying off ashes etc and it would seem a dirty sauna is , to me at least , counter productive.
Another bit of information which may be of use is a little experiment we did with our bread oven regarding fuel. We have used faggots , bundles of sticks and twigs rarely thicker than your little finger and they burn hot and quick with not a huge amount of ash. Good way to use up what would otherwise be rubbish. We tried larger pieces of wood and that didn't work anywhere near as well and didn't adequately heat the oven. There was a ruling in London ( 14th or 15th century I think) banning the use of straw so of course we tried that too. Works , just about , but it involves a constant feeding in of a small handful every few seconds or else it just doesen't burn. The same applied for chipping om a planing machine although hand shavings work well. However , both the shavings and the straw are messy to use and the floor got covered in bits so perhaps not the safest idea.
The thing is I would love to do a masonry heater type sauna at some point. I just have no experience with stone masonry whatsoever, maybe I learn from this building and one day build another one. I guess getting one of these would be the best option for the inside to be honest making a stove would be such a pain I guess https://www.ebay.co.uk/itm/222212930035. The good thing is teh building on the outside will still look great and have a nice stone finish.
