ramming or not?

[rebeccac]

Please someone help me.

I've read so much about Limecrete and its all different but we've moreorless decided on a mix and method but now I've just read that after laying a floor will be 20% higher than desired so it needs 'ramming down' !

The old House Book by SPAB clearly shows a limecrete floor being laid without instructions to ram! What will happen if we dont ram it down?

what to do ?

 

[Jon Maine]

Ramming will consolidate the aggregate closing up the air gaps and making it far more solid. I suspect if you don't do it you may suffer from it becoming friable and falling apart.

 

[JoceAndChris]

Purely out of interest (I'm afraid I offer no practical advice whatsoever) why don't you want to ram it down?

 

[Penners]

Jon, would a vibrating poker be useful in this context? I wonder whether ramming carries a risk of crushing the Leca.

(Anyone who enjoys doubling an entendre - here's the best chance you'll get for a while).

 

[JoceAndChris]

Penners! :shock:
No wonder Mrs P moans at you when you publicly confess to crushing, ramming, poking and vibrating poor old Leca! Who is she anyway?

 

[Jon Maine]

Oh such smut

Probably not wet enough to benefit from a poke with a vibrator...........

 

[JoceAndChris]

I'm so sorry RebeccaC. Please come back. It's not always like this.

 

[rebeccac]

Shame!

Back to subject I have no reason why not to do it just that so many books and websites never mention it thats all!

 

[JoceAndChris]

Well, I'm afraid I have read no books on it at all, and yet it seems clear to me that if you want it to come nicely you had better give it a damn good ramming.
Sorry, I meant come out nicely.

 

[MdB]

My belief is that concrete has to be compacted to get rid of air bubbles so as to get it to full strength. It is standard practice I believe and there are all sorts of tools available to help. I see no reason why limecrete would be any different. It might not get mentioned as it is one of those things that most people know needs to be done.

With the small patches of limecrete I made recently, hitting it with the trowel caused the lime to change into its more fluid state allowing it to combine easily into one solid wobbling mass (which I must admit was quite fun to play with) so compaction and smoothing off was easy. It is possible that I had the mixture too wet but I don't think so as I've had no shrinkage and no cracks. Very much not an expert though.

 

[Jon Maine]

I imagine it was maybe wetter than it should be, however I am inclined to think that vibration is the solution, perhaps a wacker plate with the vibration minimised may be a good solution. As I understand it a wacker plate is just an off centre weight being spun at speed, so reducing how much the weight is offset could well produce the correct result.

 

[chuckey]

As I understand it, Leca is made of little clays balls with air inside them. If the mix is too wet, would they not tend to "float" upwards, leaving the lime mortar at the bottom?
Frank

 

[Penners]

As I understand it, Leca is made of little clays balls with air inside them.

Yes, that's exactly what it is. It's clay Maltesers. As to whether it floats in water, the answer is - sometimes. Some balls are obviously denser than others, because some of them float and others sink.

So you may have a point. Perhaps too much disturbance of a wet limecrete mix could cause some of the aggregate to start making its way to the surface.

 

[Jon Maine]

As I understand it, Leca is made of little clays balls with air inside them. If the mix is too wet, would they not tend to "float" upwards, leaving the lime mortar at the bottom?
Frank

I don't think they would, apparently some will float in water and others not the heavier ones would probably hold the others in place. Although if to wet shrinkage may be a problem.

 

[Flyfisher]

I don't think the issue is Leca's density relative to water, it's its density relative to limecrete. My guess is that all Leca balls would be less dense than limecrete and that vibrating the mix would mobilise all the constituents causing the limecrete to 'sink' and the leca to 'float'.

I wonder what the professional advice would be?

 

[ljn]

I have just had a limecrete floor laid.
The earth it was laid on was solid chalk, so no need to compact that.
A geotex breathable membrane covered the chaulk and on top went 19 cm of pomice made from recycled glass - equivalent to the expanded clay. That was compacted with a wacker plate modified to spread the load (plate twice the sise welded to the original plate. That made the pomice settle and created a flat surface for the limecrete. Another layer of geotex membrane was placed on top to prevent the limecrete from seeping into the insulation.

The limecrete was mixed with the leca aggregate with a forced action in this thing: http://www.limecrete.co.uk/index.htm
The mixture was like a dense porridge, too dense for the aggregate to float in.
The screed was poured in, shoveled in place and leveled with a long baton and trowel.
Although the mixture was too dense for things to float in it, it was too liquid to walk on, so you couldn't compact it.

I was instructed not to walk on the floor for a week and to wet it with a hose pipe.

That's as far as I've got.

My next step will be to lay underfloor heating pipes and another 7.5 cm limecrete screed with denser aggregate glass, marble etc on top. That will be my finished floor. My intention is to grind/polish the surface.

As it isn't a common finish, I'm doing some research on traditional limecrete floors.
I've seen some 500 year old ones in Florence. The little dents where the surface has been hammered down with some kind of wooden pole are still visible and the surface is as strong like concrete and has survived light industrial use such as garages, printing shop with heavy equipment.

I have also been looking into traditional venetian terrazzo. The lilmecrete base with smashed tile aggregate and brick dust was compacted. Then a screed of lime and brick dust was troweled on top, marble chips placed on top and pushed in. The key is to never have one chip on top of another, or the top on will come loose. Also the chips should be pushed in but not completely embedded. Then, when it is set, another layer of lime with brick dust and marble dust is trowelled on top to make a flat surface. The floor is compacted at various stages with different instruments. The final floor is achieved by grinding the surface to expose the marble chips. Most of the floor materials were recycled from waste from the building.

The info I have found is in Italian. Many of the terms are in local trade speak from 500 years ago, so it is difficult to tell what the tools they talk about actually look like. But there is certainly a lot of compacting going on.

 

[Gervase]

As ljn says, provided the sub base and the insulation is well compacted, the limecrete doesn't need much work. It's laid much dryer than a cement slab, so vibrating pokers and other agitators don't really work. The usual way is to use a tamper bar - a balk of 4x2 cut as long as is practicable with an upright handle at each end, and just have two of you move across the surface with that, raising it a couple of inches and dropping it down to consolidate the mix and push any air pockets out. To get the top screed absolutely level you can use trammel bars fitted temporarily to the top of the slab and work the screed level with those.