rammed earth floor Limestone...any advice?

Dear Permies,

I'm happy to say I'm moving to a limestone cave in Spain.
This is the original earth bermed dwelling!


I want to do everything as harmoniously close to nature as possible, so I'd like to do a rammed earth floor.
I'd like to use the stuff the cave is made from, which is a crumbly limestone...... there is no good clay soil in the area so that rules out doing a cob or poured earth floor.

I'm a NOVICE....so I'd appreciate any and all advice from someone who's done one of these, or who knows the properties of limestone.
I'm using a combination of methods by Frank Meyer( source Geiger Institute) and Japanese Doma/Tataki floors. Thank you to these good people for sharing.

As far as I can tell I need to:

1/  Excavate to 15 cm
2/  Lay 6 inches washed gravel/Leca/pumice (depends on cost)
3/  Compact to 3-4 inches with gas tamper and level
4/  Lay a 2 inch layer of river sand, followed by a polyurethane DPM, followed by another 2 inches of sand. It rains October to March...not heavy, but I think a DPM is wise?
5/  Lay a 4 inch layer of crushed limestone mixed with hydraulic lime and a little water, and tamp to half depth. Level.
6/  Dampen surface and lightly sprinkle straw evenly over surface.
7/  Repeat steps 5 and 6...(no straw)
8/  Hand float with a slurry of the finest sieved limestone/silt mixed with a little lime and water.
9/  Leave to dry out slowly for at least a month.(cover with straw mat/hessian and dampen from time to time to slow drying process and minimise cracks.
10/ Seal with 3 coats gradually thinned linseed oil...the kind without harmful solvents, leaving to dry between each coat.


Advice anyone?

Many thanks

cavewoman.

Hi Cath, welcome to Permies,

Your system is a little more complex than is necessary, but to give an accurate example of a simpler system that would be cheap and easy to install, I will need more info about the floor of the cave, what it is composed of and how deep. A picture or two would help as well.
Three layers of; degraded limestone mixed with lime and pumice should work well straight on a clean limestone base, no sand, gravel or edpm needed. A hydraulic lime is not necessary if you use pumice as an aggregate since it is a highly reactive pozzolan. A good example of this mix is the Roman Pantheonwebpage.

All Blessings,
Bill

Hi Bill,
Thanks for the welcome, and for taking the time to reply.

What a relief..... I wasn't looking forward to making this floor as planned, and anything simpler and cheaper sounds great to me.
I will get back to you with pictures soon...been working away for a few days.
Warm regards,

Cath

Hi Bill,
Please find pics attached.

The first one is a closeup of one of the cave doors. There's a channel dug in front of it showing the limestone soil. (When you remove the soil, it expands to about 3-4 times its volume, because it's been compressed over centuries)

The second pic is the front of the cave...the entrances had already been enlarged when we found it.

The floor can go as deep as you want to dig it...also composed of layers of compacted limestone, clay and silt. Apparently the whole region was under the sea millennia ago.

I don't know much more than that....I'm in the UK right now, but will be going back in two weeks time. I'm going to do some simple field tests on the soil to determine ph and particle content....the size of the particles mostly. I don't speak Spanish....yet...so it's very hard to get reliable information. Most people there just slap loads of concrete on the floor and sides and hope for the best.
Some of the caves I've seen suffer from damp, but as long as you leave a window open, all is well.....I'm told.
This one is South-facing, so pretty dry inside. The walls had already been sprayed with concrete, so there's not much we can do about that...we will plaster them with lime plaster and then white wash with lime...so they can "breathe" .....the normal practice there.

I hope this helps...any simplification of the floor recipe would be good.

Warm regards,
Cath

I agree with Bill, if you can get to a solid base you don't need a gravel base.  Though if you can't get to a solid base the few inches of gravel is probably necessary.  Once you have a good base I would do two layers of the coarse limestone/lime followed by the finer finish layer.  I wouldn't do any membranes or straw layers between.  The thickness of the layers partly depends on the grain size of the aggregate (limestone chunks).  The layers should be at least twice as thick as the coarse fraction.  Therefore, screening the aggregate can decrease your layer thicknesses.  The total thickness of the three layers combined should probably be at least 3 inches, but that will depend on the material properties.  This floor will take time to build since you need to allow some curing between layers and a decent cure before oiling and time between oil applications.  Also, I prefer using decreasing amounts of thinner with each oil application.  On the earthen floors I've done, the first and second oil applications have more thinner than later applications and they are applied warm (oil heated on a double boiler).  I think you get better penetration of the oil that way.  At least my floors tend to take more oil than others I've talked to.

You should make a few test pads of the floor design before doing the whole thing.  Use some scrap lumber to make frames (several square feet each) and try different mixes, layer thicknesses, aggregate sizes.  Once assembled, allowed to cure a while etc. observe extent of cracking, shrinkage and abuse them to see which holds up better.  You could make the test patches outside as long as the bases you build them on is reasonably solid.  

Also, think ahead if you want to run plumbing or electrical conduit beneath the floor

Hi Ardilla,
Thanks for the information.... So happy not to have to buy gravel or use a toxic DPM!

-Yes...the base is solid...I will level it as much as possible before adding the layers. I'm assuming it doesn't have to be perfect?

-Good point about the thickness of the layers...I'll make a screening square from lumber and metal mesh to make the final layer...and apply the oil as you suggested...that confirms what I've learned so far.

-Question: How do you know when the floor is ready for the next layer of limestone mix? oil?

-I take your point about doing the test blocks....it seems that's the general advice.  I really don't want to put all that effort into the floor only to have it fail.

-Good point re plumbing.

-Question: In your opinion...do you think this floor is suitable for a shower room?  I plan to have natural flagstones to step out onto.


Thank you, thank you and thank you again.

Bill...are you out there? Any more pointers?  Anyone?

Warm regards,

Cath

Cath Brown wrote:I will level it as much as possible before adding the layers. I'm assuming it doesn't have to be perfect?

IMO the closer the base is to perfectly level the better.  Then you can use screed sticks to build the layers (change the direction you lay the screeds with each layer).  You will likely create small hills and valleys with imperfections in screeding and troweling.  However, if you start with a level base they won't be that noticeable.  If you try to level the layers on the fly, the hills and valleys will be bigger (and it will take longer).

Cath Brown wrote:-Question: How do you know when the floor is ready for the next layer of limestone mix? oil?

The lime/limestone should have done most of its shrinking (if any) before adding another layer.  The oil should not be tacky or gummy at all before adding another layer.  A week between layers/applications should be enough.

Cath Brown wrote:-Question: In your opinion...do you think this floor is suitable for a shower room?  I plan to have natural flagstones to step out onto.

No, I do not think it would be suitable for a shower floor.  If you were to try it, I would isolate the shower floor area with a membrane. Because when water infiltrates into the deeper unoiled portion of the floor it will wick laterally.  Then you will have a moist subfloor beneath an oil sealed cap.  Nothing good will come of that situation.  The flagstone may improve or exacerbate the situation depending on the permeability and porosity of the particular stone and how it is sealed.

This is very good of you Ardilla.

Thank you very much for taking the time to share your expertise.

I'll post pictures on this thread when it's done...roughly end of March next year.


Warm regards,

Cath x

Well Cath,

I'm glad you posted pictures, since I had a very different mental image. These are man-made caves! The limestone there appears to be degrading and turning into clay, so it may be necessary to excavate up to 6" of limestone/clay/silt and screen out the stones and lay them according to size; largest to smallest. This will ensure proper drainage if necessary, which this may not be.

Ardilla seems to have covered everything, but I didn't see anything on compression. This is done by tamping the floor mix while still moist, but not wet. It will feel damp but solid. This is critical to achieving a no-crack floor, since the mix will shrink as it dries and the aggregate can be settled into a tighter matrix than when wet while the lime can flow through the aggregate, gluing it all tight.

It is not necessary to seal these floors with wax or oil if you scour the final layer with a wood float and then as it dries even further, wash over and over with a grout sponge until the floor no longer changes color. This means that it is no longer taking in water and has made it's final skin of CaCO3. Note; this is only true if you add a pozzolan like pumice or bitterns(MgCl etc.) if you want to go the Tataki routehttp://japaneseplastering.blogspot.com/2014/09/tataki-japanese-traditional-earthen.html

All Blessings,
Bill

Hi Bill,
Yes, people have been digging these caves out of the rock there for centuries, living in them and sheltering livestock, mainly goats.
This one has been widened out with an excavator to let more light through to the back...it's surprisingly light and dry inside, due to facing the sun for most of the day.

I think you're right about excavating first, followed by grading the layers, and making sure there's enough water in the mix...I understand it should be just wet enough to hold it's shape when squeezed in your hand. I'm hoping to have 2 people on mixing duties, 2 people on wheelbarrows and 2 laying and levelling. All volunteers and amateurs like me.

Pretty nerve-wracking, which is why I'm trying to do my homework in advance. I'm going back there in a couple of weeks and will do at least 3 largish test blocks inside the cave to get the feel of what mix works best.

Yes...tamping for sure.  
No oil?  Reason being? Doesn't the oil seal the floor and discourage water ingress from accidental spills?
I really like the look and leathery feel of oiled earth floors, but if it's hard wearing enough without the oil...maybe I'll reconsider. I guess I'll decide when we get to that stage.
Thanks for the information regarding the no oil method...very interesting!

I take the note regarding pumice/ bitterns. If pumice isn't readily available I guess I can get Magnesium Chloride from a chemist...or a builders yard?

Yes...I've seen that Tataki blogspot.  Will scour it again.


Thank you so much Bill...I truly appreciate you taking the time to share your knowledge.

I wish you well with your ventures.

Warm regards,

Cath

PS...as always...I invite comments from anyone who has anything more to add.

PPS... Should the pumice be in gravel or fine sand-sized form to work best?

Cath. Are you still active on here and getting these messages? Just stumbled across this forum and your post when googling earthen floors. I too live in southern Spain in a cave house so would love to know how you got on and your experiences.

Richard

Caveman