Using Wood Ash as Floor Insulation..?

Hi all...
I am busy renovating an old cob brick and stone house in Bulgaria, and would really appreciate a discussion /advice on an idea that is washing around in my mind ...  using the wood ash from the wood burning stove somehow as floor insulation.
I have tried to research this but all I can find seems to be the use in making clay/ash bricks - which seem to work rather well in terms of insulation properties at a mix of 1:1
There is a little info out there on Lime Ash flooring used in England way back when...  but it never mentions if it was insulating or not. It was just a super cheap means of making a hard wearing floor using the waste lime from the bottom of the old lime kilns that had burnt clay soil, broken tile and bits of ash and coal/charcoal contamination.

How much insulation effect will wood ash provide?  On it's own it would compress, and I guess reduce it's efficiency, but mixed with Lime, clay, and straw made into a trowlable slurry would this be good to lay as a floor surface?
At what mixtures should each material be?
How about using it as a bedding mortar over the existing floor surface ( poor mans concrete) and bedding in wood rounds or slices as floor tiles?  The wood slices should improve thermal effects.

Right now my current idea is to resurface the poor mans concrete by simply sweeping clean, then directly laying on a 4cm layer of mortar made of 20% lime, 20% clay, 10% straw and 50% ash.  I can bed in wood round or pebbles to make a decorative finish.

Would this work, do you think?  Can you see any problems, or have suggestions / ideas?
Any ideas of insulative properties of wood ash mixed or unmixed with other mediums?

Trish
Oh, I can take pics of the current floors if it would help at all...

Hi Trish -

Ash is one of the most common pozzolanic modifiers for lime. Adding wood ash to lime mortar or plaster makes it harder and more waterproof (hydraulic) than the lime on its own would be. Other additives that do similar things include volcanic ash, fired clay or brick dust, and silica. The famed Roman cements that have withstood weathering and even marine environments for 2000 years are made of lime and volcanic ash. I've done a fair bit of bricklaying and plastering with wood ash modified lime mortars and plasters, and I like the way they stiffen quickly, take a steel trowel finish for a tough "skin," and are able to handle exposure while they're still curing.

So, mixing lime putty with wood ash will definitely give you a trowelable mixture that will harden up nicely. I don't know how much insulation value it would have, but if you incorporate sawdust or straw,to give it tiny voids or air pockets, it could do what you want. Try some test mixes with varying proportions and see how they work...I'm curious too!

To get the best combination of properties, you might try a thick layer of the lime/ash/etc. mixture with lots of straw or sawdust, left rough for good tooth, and a finish coat without the insulating additive.

Phil Stevens wrote:Hi Trish -

Ash is one of the most common pozzolanic modifiers for lime. Adding wood ash to lime mortar or plaster makes it harder and more waterproof (hydraulic) than the lime on its own would be. Other additives that do similar things include volcanic ash, fired clay or brick dust, and silica. The famed Roman cements that have withstood weathering and even marine environments for 2000 years are made of lime and volcanic ash. I've done a fair bit of bricklaying and plastering with wood ash modified lime mortars and plasters, and I like the way they stiffen quickly, take a steel trowel finish for a tough "skin," and are able to handle exposure while they're still curing.

So, mixing lime putty with wood ash will definitely give you a trowelable mixture that will harden up nicely. I don't know how much insulation value it would have, but if you incorporate sawdust or straw,to give it tiny voids or air pockets, it could do what you want. Try some test mixes with varying proportions and see how they work...I'm curious too!

Thanks Phil.  How much ash do you add to your mixes?  Is my 50% excessive, do you think?
Also, is using lime putty different to lime in powder form?  I found a large barrel of what looks like putty in the old wine cellar, so planned on using that for the mix...   waste not want not :)

Glenn Herbert wrote:To get the best combination of properties, you might try a thick layer of the lime/ash/etc. mixture with lots of straw or sawdust, left rough for good tooth, and a finish coat without the insulating additive.

Thanks Glenn.  I can go to around 4cm thick max otherwise will exceed the door threshold  timbers, hope that is thick enough.
Question, with addition of straw or sawdust, will this effect the bond ability of the material to the bottom layer of concrete and or the wood slices I am planning on embedding into the mix as a finish?

"Thick enough" is a relative term. Whatever thickness you can afford or have space for is right for you. Obviously, the thicker the insulating layer, the more isolated from ground temperature you will be. If you have 4 cm total available, and the wood slices are 2 cm thick, I think the wood will have as much to do with the overall insulating ability as the clay mix. All I can say is to try small sections of various combinations and see how they feel and hold up, before doing the whole floor.

When I'm doing a lime plaster as an exterior finish, I add around 2-5% by volume to the mix of lime putty and sand and I may have tested up to 10 when I first experimented with pozzolans. I don't think you'd have any problems adding more, although you'd most likely want to test different proportions as Glenn advised. The ash will make it harden much faster than an unmodified lime plaster. So will contact with the concrete subfloor...as soon as you trowel it on, that will start sucking the moisture out of the mix.

Lime putty is just hydrated lime that has been mixed with water and allowed to sit. The longer the better...if you've got a barrel that's been sitting around that's fantastic.

Glenn Herbert wrote:" All I can say is to try small sections of various combinations and see how they feel and hold up, before doing the whole floor.

Cool - Thanks.  Right bought a bag of premixed lime and sand mortar for a test this weekend.  will try adding sawdust and bedding in wood slices and see how it performs and looks !  will keep you guys posted, hopefully with pics!

Phil Stevens wrote:When I'm doing a lime plaster as an exterior finish, I add around 2-5% by volume to the mix of lime putty and sand and I may have tested up to 10 when I first experimented with pozzolans. "

Right, going to test with various loads of ash and try see what happens.  Will keep you updated - plan on making some smallish tiles sort of thing to see what effects.


Lime putty is just hydrated lime that has been mixed with water and allowed to sit. The longer the better...if you've got a barrel that's been sitting around that's fantastic.

Well it is lime putty I presume! Not tasted it, lol..  but it sure looks like it.  Probably around 5yrs old or more by my estimate.  Not going to use it in the test, bought a bag of premix to trial with and lets see what results are first.  Will come back with photos after this weekend.

Thanks so much to you guys for input.
T

Okay, got 3 tests on the go, however after 20hrs they are still very wet.  I thought they would be hard skinned by now.  Have I done something wrong?
Could it be the plastic containers the mortar is laid in?  Or excess water in the mixtures?

The first one I made far too wet, I realise that, the 50% mix. I was trying to wet the ash.  Next of 40% and 60% I wet the ash, then added the saturated sawdust, then the lime mix and a bit more water to allow for easy mixing.
But both 40 & 60 are still very wet to the touch, no dry skin.  It's almost as if it just came out of the bag
Help??

wood ashes are a very possible poison!!!They can be  contaminated with  Al.
Given the right elements in the soil, and acid rain, tree takes it up, you burn the wood, Al is left behind.  
Placed on the garden soil, plants take it up.  This really happened during the energy crunch of 1970's
A country doctor figured out why his rural patients were getting sick!!
It may be ok, and likely is for your use, but just a word of caution,

The mixture may have had too much water in it. Since you started with damp sawdust, you might not have needed to add extra water. Sometimes you just have to mix the materials a little bit longer and it will go from being chunky and too stiff to a creamy consistency.

Doing the test in plastic may also be part of the problem. Try troweling a test patch on a section of concrete slab (it's easy to chip off if it's just a small area) to see how it acts in contact with the substrate. When I use ash-modified lime plaster and apply it over an existing lime or earth surface, it sets in a matter of minutes and I can go directly to a steel finish trowel. I usually wet the base with limewash right before I apply to improve the suction as well as retard the setup.

Whooo hooo ...  photo feast coming !  Lol..

Okay, I was unhappy with the tests in the tubs - add the word deeply in front of that.  
The objective here is to create a new floor surface over old nasty ones, to not have to rip out the old floors as physically I am unable as well as avoiding the costs of laying from scratch, and to achieve greater warmth from the floors ( Bulgaria goes to -25 C) on the odd winter).
I am also trying to keep things sort of authentic /  rustic to suit the house which is full of massive beams, cob and stone.

Those first 3  blocks look awful.  The wood inserts have cupped ( okay may have been too thin, it was what I had lying around) ; and they have either raised up or the mortar shrunk leaving the wood proud - no good for floors.
I tried removing one from the plastic mould and it just broke up, and pretty much crumbled on me.

So decided to test a cordwood mortar mix of 2 Lime/sand, 2 sawdust and 1 ash as replacement of the cement.  Bah!  Went in nice, smoothed off great, dried much better - BUT - it is incredibly weak...  I can literally crumble the mix between two fingers.  Again no good and the wood cupped again.

Then I read your reply Phil and went directly onto the hallway floor ( think it is an old lime mix with pebbles for a harder wearing surface) - dampened it down, laid a load of just Lime/sand mortar and embedded the wood slice.  I did however dunk the wood in water so it did not suck too much moisture from the mortar - not previously done an any of them. No additives at all. I laid the wood flush with the surface.  
Result after one day - slight shrinking of mortar around wood, no cupping evident so far and it has skinned over nicely to the touch.

In the kitchen on the concrete I dampened off, laid a dusting of ash, blob of Lime/sand mortar and embedded the dampened wood, but then dusted the mortar fairly heavily with ash and smoothed it off.
I love the way the ash has allowed for an almost glass finish compared to plain mortar.  So far after one day it has skinned over but feels slightly tacky to the touch, no evident shrinkage against the wood, feels a little more damp than the hallway - but on concrete and no ventilation compared to hallway - and holding its smooth finish.

So far looking good.  Time will tell.  If I can keep the cats from embedding a paw print in them, will take pics again later as they dry off further and post.


My conclusion (for what it's worth) is the sawdust is no good for floor purpose as it weakens the mortar too much, and using less will not provide any insulation properties.  Even if you skimmed with plain mortar afterwards, I would worry about the under layer breaking up under pressure or constant foot traffic and cracks forming.

So far it looks like higher quantities of ash could retard setting but does provide for a really great smooth finish when used as a surface treatment dusted over the mortar.
But it is not a fair test as they were not laid on the same surface.
I do have a bit of lime mortar mix left, so could do some more tests...

What do you guys think?

That's good progress, Trish. I think cutting out the sawdust was a good move. By the looks of the pictures, your mixture and technique appears workable and you have got the shrinkage under control. So, more testing? Or are you getting close to the effect you want to achieve?

One more thing to note: Lime plaster and mortar hardens by carbonation. This involves absorption of CO2 from the air, and it happens faster when the lime is damp (not soaking wet). So, to get a durable floor, you may need to cure it for some period of time with controlled moisture levels and avoid letting it dry out completely. Counterintuitive, I know. It may just be a matter of misting it once or twice a day as it's curing.

Interesting that you have an existing floor that is lime with pebbles in the hallway. I wouldn't be at all surprised if there was ash mixed into that, as it was a common floor material in Europe and Britain as far back as medieval times.

Hi Phil.  Glad you think it appears workable.
Yes, more testing due but I do want to wait a bit for a week at least to get a better cure and prove the two test "blobs".  Both for shrinkage and the wood slice staying in place, and adhesion to the bottom surfaces.

Then will test with the actual wood I plan on using, oak firewood that has been curing for 2yrs..  not rounds but pretty much square bits from splitting the firewood that I will try to cut into 2 inch pieces to embed.

The hallway floor I presume is lime, I am not skilled enough to know.  Sadly the previous owners skimmed it with cement which has cracked all over and lifted, pulling the surface with it so it is dusting a lot now.  There was also linolium laid over it so when I got the house it was damp and nasty with mold there. Dosed it with vinegar

But back to floors, will give it a week to cure, keeping them a wee bit damp, to prove the results.  
Will keep you guys posted on results.

Thanks so very much for the input.  Much appreciated.

Oh - if anyone is interested in pics of the house and refurb currently being done, can post some. Like gypsum plastering the ceiling between beams, repairing cob render on stone wall, bashing in walls to join rooms together etc. And some of the features of a traditional Bulgarian house.

Yes, please post pictures of your structure and work. Such things are always interesting to me and I am sure to others here.

Okay - just for fun here are some pics of my place. Bulgaria, although a member of the EU is a post soviet rule country and in many ways is way behind in many things - which is what I like about it.  Rules and regulations are minimal, life is basic and simple.  

This is what I guess you would call a root cellar, a room with little/no ventilation, cold and damp.  Ignore the jumble of "stuff", but you can see oak shelves along the back and side walls, bare underside of ceiling beams caulked with mud. Walls are stone and cob  plastered.  Floor is poor man's concrete caked in mud from previous owners tramping in and out from the fields.

This is being converted to my kitchen / dining room.  I broke down one wall into the adjoining room, and bashed in a new doorway to the lounge for access between the upright support beams.  Broke down the front wall of the house / dining room, which was mud brick and installed  windows in a new stone wall.
The ceilings are gypsum plaster over a plastic mesh nailed to the oak panels, and mud caulk where it was too difficult to plaster  between awkward bits.   Walls are limewash with a bit of tint.

kitchen is coming along slowly. Walls and ceiling painted in lime wash, lights installed and some temporary work space too cook!
The beautiful dresser was a thrift shop find for 250 lev ( $100) painted poo brown, I have dry brush painted over the brown with a lighter colour.  Those baskets are full of walnuts from the trees in the garden.

Some interesting bits and bobs around the place...

There is a barn attached to the house, as well as 2 separate barns.  The one attached has a wine cellar with brick paved floor with a channel running outside to take spillage out, and for washing down the floor after making Rakia.

The lounge has the remains of a clay bread oven behind the wooden  doors.  All that remains is the metal door to the oven,  the oven itself was demolished long ago but they are still used here a  great deal.  Traditionally Easter time once the bread comes out, the lamb goes in for the Easter feast.  There is a new "lamb oven" as they call them now build out in the garden.

Some of the rooms have a small window in them between 2 rooms.  Discovered it is a "Candle window", so one candle or lamp could light two rooms at the same time.

Top lounge area has traditional fireplace made from cob, metal damper is just a sheet of tin  cut from a barrel or something and a metal hook to hang your pot over the fire on.  Sides have niches for keeping something warm in or proving bread dough.  The walls were painted with a chalk paint, possibly home made because it literally wiped off on your hands. These have been washed down and lime washed over for now.

Everything is painted a  horrid institutional green, think it was a free giveaway paint during comunist rule or something

Downstairs bedroom.  Excuse the unmade bed
Removed panel from to expose beam, repaired plaster in some places, exposed in others.  Waxed original floorboards. Nwe double glazed window and a slap of paint.
The funny wood thing in the foreground is a traditional swift used for winding wool onto after spinning.
Traditional Kilim or wool rug on the floor.

Trish;  Thank you for sharing your photos!  You are doing a fine job of improving your old home.
My home will be 90 years old soon... just a baby compared to the European homes.

Thank you Thomas.  
It's a slow work in progress but a creative one.  I actually don't think the house is that old.  We tend to think of this type of build as being old in our western environs, however they still build like this today out here. The beams are hard to get now of course, however villages are poor and still use whatever is to hand to build with.   My house is by no means unusual for Bulgaria, along with the fact they are extremely cheap to purchase.

1 acre of land along with barns and house sells for - area depending - around Euro15k. If the house is a  pull-down, literally falling apart you can buy for less than half that.

It's a fail again I'm afraid.  

The kitchen test cupped again, but hallway did not.  However both were not able to sustain any kind of pressure placed on the disks, with the mortar breaking away.

I think this will continue failing, because the wood is embedded into the mortar, on a wet mortar base.  When researching it has always been a case of using construction adhesive to fix the wood to the subsurface, and then using either cement mortar, lime mortar or a mix of grout/sawdust as a grout between the wood shapes.

My objective of trying to gain an insulating base under the wood is not working this way.  
The only way around this I can see is to lay in two stages, lay a base of lime mortar and let it cure fully.  Then glue the wood to the new base, then grout with lime mortar.  I would be worried about the grout mortar not attaching to the under-layer though and breaking away under foot traffic. So would have to possibly go for a true tile grout.

Any input or suggestions..?

Trish - I think the only thing you're going to successfully embed in a lime mortar (or any hard masonry-type substance) is something which does not expand and contract. Especially not something which swells when it gets damp and shrinks when it dries. Pebbles, tiles, glass bottles, pottery shards, etc. If you were doing a wall or surface that didn't see any traffic or pressure on it, you could get away with the wood rounds losing some contact with the grout. But in a floor you really need everything to be bonded to the substrate and locked in from all sides.

What about a coating of the lime-ash plaster as a leveling substrate with wood rounds laid over the top? The voids between the rounds could be filled with sawdust and small chips, then the whole floor flooded with linseed oil. You'd pretty much be making linoleum in place. Once the oil polymerises, the whole thing would be a big sheet.

I agree Phil.  It is doubtful the embedding idea is going to work.

So what if I change  tactic - look at this pic.  Tried hard to find more info on it but nada - just shows up in lots of "rustic decor" posts.  But I think I am falling in love!  

On the concrete floor in the kitchen, I could drill holes into concrete and screw the boards to the concrete with brass screws.  Means I dont need to smooth or level the floor. Then grout with lime, and wax the  whole sheebang afterwards to seal a bit for kitchen spills.  And whoo hoo no cutting on the chopsaw so time saved.

Bit  more difficult in hallway as cant screw into that strange pebble/lime supposed  mix, so will just have to lay in situ and grout around it.  At least the hallway is relatively level and smooth as opposed to the concrete in the kitchen.  I am suspecting the key here is to have relatively large gaps between boards to provide the strength of the lime.  
To slim between boards  and it may crack and break up, so strength will be in depth and width of lime grout?
The wood will provide the insulation.  Not a whole lot of it, but better than the raw floors now.  
Or...   Could  I get away with a thin layer of EPS under the boards, then grout with lime mortar do you think?  Maybe the 1cm  thick stuff?

Hi Trish;  I see what you mean about falling in love! That floor in the photo is OUTSTANDING!  I hope that it works for you !  Keep us posted!

Yes, beautiful floor look!

I don't think you would get away with a continuous layer of foam under the boards, even if it is laid into wet grout so there is 100% contact on the bottom. With individual boards, there will always be an edge or end that can be stepped on and make a concentrated load that crushes a bit of foam.

You might be able to use strips of foam 10-20cm wide with a couple-few cm of solid grout between them, giving a rigid base so boards can't flex. That would be less insulating than continuous foam, but much better than none. In this case, I might use 2 or 3 cm thick foam. I would run the foam perpendicular to the topping boards so all boards have rigid support at close intervals.

thomas rubino wrote:Hi Trish;  I see what you mean about falling in love! That floor in the photo is OUTSTANDING!  I hope that it works for you !  Keep us posted!

Yeah, pretty amazing hey.  I need to do a barn scratch n see what wood i have in there.  Somehow this just wont look as cool with new wood, I just know it so hopefully have enough old stuff in the barn.

Glenn Herbert wrote:

You might be able to use strips of foam 10-20cm wide with a couple-few cm of solid grout between them, giving a rigid base so boards can't flex. That would be less insulating than continuous foam, but much better than none. In this case, I might use 2 or 3 cm thick foam. I would run the foam perpendicular to the topping boards so all boards have rigid support at close intervals.

Erm..  okay feeling a bit silly here, forgive me. Are you saying laying "boards" of foam say 20cm wide North/South with a gap between each, then putting the wood boards in an East/West direction, and filling in the gaps between wood boards with grout?  This would make a sort of cheque board effect of deep grout to subfloor and shallow gout on top of foam in other places?

Or could I just lay the whole floor with foam boards, no gaps, lay my pattern of wood boards with decent gaps, then trim out bits around the boards to get grouting down to sub floor level.  Means under each wood board is solid foam insulation and only the grout lines will be uninsulated.

Trish, what did you end up with for the flooring? Did you go with the wood planks? I'm in the process of buying a Bulgarian house (not as traditional as yours, sadly, but I still like it!) that like yours has been "improved" by adding rough skimmed concrete floors, probably straight on bare earth.

Jane Mulberry wrote:Trish, what did you end up with for the flooring? Did you go with the wood planks? I'm in the process of buying a Bulgarian house (not as traditional as yours, sadly, but I still like it!) that like yours has been "improved" by adding rough skimmed concrete floors, probably straight on bare earth.

Hi Jane,
Nope, I gave up in the end with the wood rounds flooring.
As you say, a lot of BG houses have "poor mans concrete" laid on bare earth as floors,  and are often damp and degrading.  After a particularly wet spring and mold on the floor and walls, I ended up ripping out the concrete, (now used as crazy paving on a garden path), digging down 30cm, laying 20cm crushed stone then 10cm rock dust with a weed barrier fabric between.
I then capped with 5cm sand and laid "plotchy" on this, and grouted with lime mortar.

it has solved the damp issued totally, and is surprisingly warm in there.  I have not sealed the floor, afraid of damp still, so it does tend to show marks re being in the kitchen area, but I can live with that :)

Thanks for replying,  Trish!

"Plotchy"? I've no idea about that one.

I suspect I'm going to have to do the same, dig up all the cruddy concrete, dig down and lay proper earth floors with plenty of compacted gravel as a base layer. My house has the same damp issues, exacerbated by the fact I can't move there yet so it's empty much of the time. These houses were designed to have fires burning all winter to keep them dry!

Just hoping I don't also have to chip all the wall render off and redo that as well. I think it's been "modernised" with cement, too!

Jane Mulberry wrote:Thanks for replying,  Trish!

"Plotchy"? I've no idea about that one.

I suspect I'm going to have to do the same, dig up all the cruddy concrete, dig down and lay proper earth floors with plenty of compacted gravel as a base layer. My house has the same damp issues, exacerbated by the fact I can't move there yet so it's empty much of the time. These houses were designed to have fires burning all winter to keep them dry!

Just hoping I don't also have to chip all the wall render off and redo that as well. I think it's been "modernised" with cement, too!

Plotchy is the large flat stones used here in abundance.  Many houses still have plotchy rooves, beautiful to see but the weight of that roof must be amazing.  most have replaced them with roof tiles now, and used the slabs (flagstones) as paving on pathways, drives and even used the smaller pieces as wall dressing on the outside.

if the cement render is outside, you can get away with leaving it in most cases.  It depends what the walls are build with.  Def remove if it is inside if possible.  Mine is stone with mud mortar bottom floor, and mud brick top floor.  it is rendered outside in cement, but thankfully inside they did not do it.
so far, its still good as it seems to be a cement wash more than anything, and underneath was the old lime render.  They tended to do the cement wash to preserve the lime render and not have to keep doing repairs on it.

Inside, i had to remove a type of cardboard ply, a cheap version of plywood - that had been installed in one of the rooms, and they had linoleum on the floor, resulting in a smelly, moldy room.  but once that was stripped out, and the floor done, the room is now fab.

The biggest tip I can give you, is go slow on any planned renovations.  If possible, live in the house for at least 6 months before doing anything.  Because you will change your mind about things when you live in it.  I changed location of dining room, study and kitchen a few times, until settled on something that works for  me.  If I had of gone with first ideas, it would have cost much more, and been only half as effective!

Thanks Trish! Right, now I know the name for those stone roof tiles. Stunning, yes, but they must weight a ton! They'd make fabulous paving. My house has those half-circledemi-lune tiles, but the roof is in poor condition - a lot of patching with sheets of metal. The whole thing needs redoing.
Part of my outside render is definitely earth-based. Part looks to be cement. Inside looks like it's been redone in cement too, at least in one or two rooms.
Good advice to take my time, even if it means camping out in a mess for a while. Got to get a feel for the house, the patterns of sun and wind and weather, before making big  decisions. So get it weatherproof, then set up camp and feel what will work best.