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Help! Wet or Dry bulk ready-mix cement.


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Help! I'm caught between two 'experts', each giving different advice.

Here's the project: I need to lay a 'Chaux' mortar floor in my cave. The area is 8m x 4.5m and the screed needs to be 8-10cms thick. It has been estimated that it will take 3 cubic metres of mortar to cover the floor, which is old brick. The source of the cement is the local builders merchant, which is only 2.9kms away. Because the access to my cave is a little narrow, it is not possible for a cement-mixer lorry to deliver ready-mix cement to the cave.

Therefore, it has been proposed that using a sided, flat bed tipper truck of a friend, wet ready-mix cement will be collected at the builders merchants, (about 0.5 cubic meter at a time), transported the 2.9kms to my house where it will be deposited next to the cave entrance on a large tarpaulin. A group of us will then proceed to quickly barrow and tip the cement into the cave where it will be levelled and smoothed off on top of a wire grid. Then the truck will fetch another load, etc, etc.

The guy who owns the truck and another 'ami' who is in the building trade assures me that the cement will remain workable as the distance between the builders merchant and my cave is only a few kilometres and will be a just 4-5 minutes drive.

However, another friend who has done a lot of work for me in the past says the best thing would be to hire a large cement-mixer, buy the cement mixed with sand, dry 'en vrac' from the merchant and mix it at the site. The reason for this method, he says, is if I buy wet ready mixed cement, by the time the cement reaches the cave, it will have lost a lot of water due to transportation vibration and will start to go off by the time we are laying it.

I don't know who to believe!

My 'dry-mix' friend is an older, experienced Jack-of all Trades and quite 'old school'.

But I don't really want the faff and expense of having to hire a large cement mixer, when I can purchase the cement all ready to go.

Can any one offer their thoughts on this? Will the cement go off that quickly?

We are in the Centre (41) and I hope to have the work done in early June, so it should not be too hot.

Any advice would be gratefully received.


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[quote user="Matelot"]by the time the cement reaches the cave, it will have lost a lot of water due to transportation vibration and will start to go off by the time we are laying it.[/quote]With all due respect to your friend I'm afraid I'm at a complete loss to understand how vibration would result in a loss or water, perhaps you could ask him to explain the mechanism by which that occurs ?

30 minutes is reckoned to be the nominal time for the initial set for ordinary cement however you can add a retarder to extend that.

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There is a really good reason why mixer trucks rotate.

Why not have the bulk delivery but shoot it into the trailer bit by bit and barrow into place.

3 people, 3m3 easy with an on site mixer how much is the hire compared to purchase and sell on?

With a tarp on the top of the mix the air from driving won't dry the water off if you really want the hassle, hope there aren't any speed humps [:)]

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Hi Matelot,

OK, you may risk losing some of the water in the mix as the lorry bumps down the road.  But remember that most of the water in the mix is only there to make it workeable, i.e. it's not required to make the cement set.  So, should the need arise, you can always add a small amount of water once the mix arrives on site (but see ps below). 

But essentially my advice is the same as AnOther: talk to the batching plant about adding a retarder.  As you may imagine, you're not the first to have been confronted by this kind of problem [:-))].  Even in the UK, batching plants can be some distance from the construction site and the solution is to add a retarder (and keep the drum turning.; but that doesn't apply here [:)]). 

Also, be sure to let the batching plant know what the mix is for, i.e. a floor.  They can then design the mix so that it flows well and self-levels as much as poss (by selecting the most suitable aggregate and/or by using property modifying additives).  You want to make this job as easy as you can.  Unless you really like making life hard for yourself, don't try knocking up 3 cubic metres of concrete in a mixer ...

P.s Just be aware that all that excess water has to escape somehow.  It does this by evaporating through micropores in the concrete.  However, if it evaporates too fast, you risk getting cracks in the surface of the slab.  To stop this, once the slab is laid, cover it with sheets of polythene as it cures. If it's really hot, lightly spray the top of the slab with water.  But again - not too much!  Otherwise the top of the slab can turn dusty.



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Can you get a "Toupie" with a "Tapis", the conveybelt delivery system which is quite narrow. It might be able to poke down into the entrance of the cellar? Have had one delivery with one once and it had a good reach.

On the water side, if you "float" up wet cement or even oats and milk using vibration, you do get a lot of liquid coming to the surface and the aggregate/oats sinking. I presume the same principle would apply to the vibrations of wet cement in a lorry bed?
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Matelot wrote:- ''Here's the project: I need to lay a 'Chaux' mortar floor in my cave. ''

There followed various comments about cement.

As I understand it, chaux mortar is made using lime and sand not cement and sand, so why questions / answers regarding cement ?
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Well, 'cos Matelot then goes on to talk about cement, not lime, starting with, "The source of the cement is the local builders merchant ..." and then, "it is not possible ... to deliver ready-mix cement to the cave" and, "wet ready-mix cement will be collected .." etc etc.

But I agree there does seem to be some confusion about exactly what we're talking about ...  [8-)], which is kinda important given that cement and lime don't share the same handling and curing/setting properties.

P.s And, of course, it's not 'cement' anyways in the last two examples quoted above, 'cement' being correctly a "Powdery substance made by calcining lime and clay" (OED).  Add an aggregate to it, and it becomes 'mortar' or 'concrete'.  But hey, that's just being pernickety...[:D]

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Thanks for all the advice and replies folks!

Apologies for not making my post clearer! It is plain to see that I am not a builder!

I need to lay a floor that is either chaux mortar or concrete (béton). The option for chaux is to buy bags of lime and a load of sand, hire a large mixer, mix it on site, barrow it in to the cave to lay and spread it. I was under the misapprehension that pre-mixed chaux mortar could be bought in bulk. Apparently this is not the case. Mixing on site is also an option with dry ready mixed sand and cement that can be purchased by the cubic metre and loaded on the back of a truck.

The other option is to purchase ready mixed wet concrete. This would have to be loaded on the back of my friends truck, 0.5 cubic meter at a time, driven 3 kms and dropped just in front of my cave onto a tarpaulin where it would be shovelled into wheelbarrows by two or three of us and then barrowed into the cave, (a distance of approx 8 meters), dropped in place, spread and levelled off. It should take about six loads from the builders merchant to complete the work.

I need to add that my cave is not a cellar. It is a 8m x 4.5m room straight into the hillside rock with a barn door. (Caves such as these are in abundance in this part of France.) However I do not have room (or the funds!) for a cement mixer lorry with a 'tapis' to get onto the property, hence the need for mixing or delivery on site with a smaller vehicle.

I am inclined to go with the wet ready-mixed concrete version as there should be 4-6 of us to do the work and I am advised that there is a working time of at least 30 mins before the concrete starts to go off. (The journey time from the builders merchants to my house is 4-5 minutes) .

Also the work should be done in one day. Using dry materials will take two or three days, and as I am paying a couple of guys for their labour, keeping within budget is important.

Thanks again for your replies.
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I would do it by hand and it will be a lot cheaper. With the labour you have, one mixing, one carrying one laying you should be able to do it in less than a day.

3cu is around 3000 ltr and if you hire one of the big cement mixers , you can get a 110ltr at least, then it should only take you 30-40 loads.


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