An anecdotal introduction to CPAC (ready mixed concrete)

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An anecdotal introduction to CPAC (ready mixed concrete)

Postby jazzman » Wed Dec 13, 2006 1:55 pm

CPAC: All you need to know about it and were too afraid to ask.

Where and how to buy.
Concrete is one of the materials you will spend most money on so it's really worth looking into the options. Here you have up-to-date info on prices and where to buy. For what to use for which jobs, the other posters have provided adequate information.

CPAC vs. hand mixing:
CPAC (Ready-Mix) is a boon - hehe, nice pun on the Thai word for cement ;) - as it really does save a lot of labour, and this is why you should make it clear with any workmen you hire to build your house or a driveway or a long perimeter wall, whether their labour includes for hand mixing or using CPAC, and (to reiterate an enormous argument with a rather impolite poster on another topic) whether the price includes for tools. Note that once you've even mentioned CPAC, they won't have it any other way because 1. They HATE mixing concrete because they don't know - or don't want to know - how to use shovels and 2. They know you can afford CPAC. 3. They know that it take three or four times longer to do the same job by hand mixing. The phases of building a normal sized house (except for laying the roof tiles) never usually take more than about two days each. Thai people get bored very quickly by days of repetitive work.
Whether to consider using CPAC as an alternative to hand mixing depends on a couple of factors:
    The volume of concrete needed.
    The time it will take to lay it -e.g. did you make the mistake of building your interior walls first?
    Whether or not you have your own cement mixer or can hire one cheaply.

Volume: You're not going to get more than about 200 - 250 Kg per load in a normal sized cement mixer. This is about 4 or 5 wheelbarrow loads. A cu.m. weighs nearly 2 ton, so that's nearly 8 mixer loads or 32 -40 barrowloads. A lot of hard work :( so if you are going to need 1 cu. or more it may be worth asking your local CPAC man what the minimum qty is he will deliver.
As a rule of thumb, 1 cu will do 10 m of 1m wide garden path - that's about the length of one side of an average house. See Xpat's posting below for a link to a volumetric concrete calculator.

Time: CPAC means being at the receiving end of a lot of concrete. You and your workers have to keep going until the load is poured and spread - you can't break of for sandwiches and cups of tea or som tam and laow kaow. This can involve hiring extra labour for the day.
As a rule of thumb, 14 cu (2 loads of 10 wheel CPAC truck) will do 120 - 140 sq.m of the ground floor of the average house. One load in the morning and one load in the afternoon. The labour still won't get a lunch break; while the truck goes to fetch the 2nd load they will be busy spreading, adjusting and smoothing the first lot.

A Cement Mixer can be hired, but a daily rate will probably be preposterous. We hired ours for the duration of our project, an estimated 3 months, for only 500 baht, and came out of the lump sum for the labour which included them providing their own tools. I don't know where it came from - the workmen said they would take care of it. Someone once suggested buying a cement mixer and selling it again when the job is finished. Look into the price of second hand mixers to see what you'll get for it, if you think you'll be able to sell it. Finding a second hand mixer to buy is very difficult. When people buy one they tend to hang on to it and hire it out :)
Cost to buy: 5,000 - 7,000 baht and usually sold without an engine or electric motor. A Chinese copy of a Honda petrol engine will cost another 3,000 - 4,000 baht. An electric motor, which needs to be powerful will cost about the same.

Concrete Vibrator: At some stage in the proceedings, if you want your concrete to be really firm, particularly for deep things like foundations or pillars poured in upright formwork, or where it has to work its way into complicated shapes, it is highly recommended to use a vibrator.Your builders probably won't use one of you don't insist on it, so you will have to consider buying or hiring it. For one house, plus a swimming pool (for which it is absolutely necessary), after which a cheap one will probably be ruined, you can buy a vibrator with a 1,5 m thingy for as little as 4,000 baht. Professional ones like Limey's (if he's got one - he owns 1/4 mio baht's worth of tools...) to last a lifetime will cost 10,000 - 15,000 and come with a very long (2- 4 metres) thingys.
Tip: If you use one of the shorter models, you can lower it on rope into deeper shafts. Pause the pouring to vibrate with the addition of each layer of every 60 - 80 cms for a minute or two.

Whacker Plate: And while we're on the subject of large expensive tools for concrete, to be sure your ground and/or hard core is absolutely firm, (particularly if you have had your land filled) you should consider going over it with a whacker plate. This is a petrol driven compactor - see pic on Dozers's main pages. I never looked into the price of buying one here, in the UK the cheapest one costs 480 quid (33,000 baht) but the Thai price would of course be only about half this. When we need one, we hire it from a local building contractor for 200 baht per day, so we plan ahead to get as much use out of it as possible for the day.

A Cubic Meter of CPAC works out about double the price of hand mixed concrete, but you must remember that the supplier also has to amortize the cost of his truck and provide a driver (sometimes two) who will stay on the site until the job is finished. Delivering CPAC is not just a question of arriving ad dumping 10 tons of concrete for you and your changs to spread around the place. See the prices below.

Planning: Getting the stuff dumped exactly where you want it is not as easy as it may sound. If you made the mistake of building all your interior walls before pouring the floors, you will have to organise your labour in relays to wheelbarrow it to where it is needed, and planks will have to be laid across your sand/wire-mesh to push the barrow; it sometimes takes two men to move the barrow, one pushing, one pulling. This planking all has to be shifted again and again as the work progresses. At the end of the day you will feel that you have defeated the object of having CPAC delivered.
When planning your house, be absolutely sure that a large truck will be able to back up to within a maximum of about 5m of where you will dump. They use large diameter blue PVC pipes cut in half longitudinally for chutes and it is almost impossible to send the stuff round corners.

Time factors: Five experienced workers will lay the 15 or so cubic metres needed for the floor of an average house (ca. 150 sq.m.) in one full working day. If you made the mistake of building all your interior walls before pouring the floors, like Jazzman did 25 years ago in Germany it will take up to 50% longer or more.
One load of CPAC will remain liquid in the lorry for about two hours on site plus the time on the road. Calculate well, and have enough people to spread it, a pile of it left standing will start to get stiff in less than 30 minutes. Get extra labour for the day if you think you will need it: at 150 baht per day per man it's not worth economising on, and risking wasting several thousand baht's worth of CPAC because you can't get finished before it hardens.

Delivery: A big job like a floor or a long concrete drive (say about 150 cu.m.) will require 2 full loads of a ten-wheel truck (about 7 cu.m per load). Some firms, particularly village building supplies outlets who make CPAC as a sideline, have the smaller 6-wheel trucks which hold 3 cu.m. These are fine for filling footings or pathways.

Quantity: How much concrete do I need? It is surprising how often this question pops up on web forums. It should be fairly easy to work out. A volume is calculated by multiplying the length by the width by the depth (height): L x W x H, or it was when Jazzman went to school, but with the advances in technology over the last 50 years, anything could have changed since the Egyptians got it all worked out 5,000 years ago. If your floor pan is a highly irregular shape with curves and things, get your labourers to work it out, you'll be surprised - they can can do it (after squatting down and much debate).

Setting:
Correctly mixed and laid concrete should be stiff enough to walk on without leaving footprints within 2 hours, but it's not recommended. If you see concrete with dog, chicken or buffalo footprints in it, there was either something wrong with the mix, or nobody could be bothered to hang around for a while to shoo them off :(
Contrary to what some people believe, concrete doe not dry, it cures. The water doesn't go anywhere, it actually becomes one of the ingredients in the chemical compound which results. CPAC is made with more water to keep it elastic for longer while it is worked, but it should not be too sloppy. There is the famous cone test, but generally, when laid concrete is smoothed over, it should be firm and and have a matt sheen to it. Pushing your fist down through it should be difficult. If it's easy, you will feel the looseness of the stones of the aggregate and you will notice that the higher layers are just water and sand. You'll end up rushing to get more dry aggregate thrown into what has been laid to give it more density and poking it down with a stick, so be sure to have a pile of gravel handy, as this often happens with CPAC - the Thais tend to put too much water in it. Over dilution - and watch out for this when they get going with the garden hose to flush the last bits out of the truck - will destroy the chemical process and all you will get is a mess of dry powdery gravel and sand.
The fact that it may be hard after an hour or two, is only the beginning of the process. Concrete needs about 28 days to fully cure, and the hardening process can continue for weeks or months. In a tropical climate it is crucial not to let the concrete dry out. As soon as it is hard enough not to absorb any more water, it should be sprayed (not soaked) with a hose then covered with sacking which should also be sprayed. The sacking should be kept moist for several days, and no structural work should be carried out on the concrete.

Shuttering (formwork) can be removed after a day or two for flat floors and footings, and should be left on pillars and beams for several days, but it is best not to disturb it at all until it becomes absolutely necessary to remove it for doing other work.

How much cement powder? Yes it is true that in Germany we do go OTT with most things, - the bodywork of a Merc is almost bulletproof when it leaves the production line. About 6 bags per cu.m is the norm. Adding more does not necessarily increase the strength, after all it is only supposed to be a binder for the hard stuff: the sand and the gravel. Cement powder mixed on its own with water and left to go hard is not strong stuff. Look at those left-over sacks of cement that have gotten wet, and how crumbly the cured powder is.
What does add to the strength is the quality of the cement powder. Here in Thailand it is usual to use the best in CPAC, because CPAC is mostly used for constructional concrete and large spans. They use Portland, which they call boon daeng because of the red lettering on the bag.

Where to buy:
Every amphoe (district) town, and most larger villages will have someone who will deliver CPAC. It is not stuff which is transported dozens of miles to the customer. You've probably driven past lots of CPAC depots without realising it. They also make concrete pillars and fence posts and the concrete rings for septic tanks too, so where you see a yard full of those things lying around, that's the place to stop and ask.

Cost: The cost fluctuates with the cost of vehicle fuel. Transport is a big factor for sand, gravel and cement powder are heavy stuff. It has to be delivered to the CPAC depot, and then it has to be mixed and delivered to your house. You will have noticed that all major construction sites like bridges, motorways, skyscrapers have their own CPAC plant with their tell-tale silos for the cement powder and sand and gravel mountains, and particularly typical British housing estates (because the UK is still the only place in the world where there is no tradition of buying a plot of land and building your own house - mainly because the government has made it practically impossible for Otto Normal Burger to get through the red tape. The building developers all wear clunky gold jewelery and cuff-links, and by coincidence, so do the officials in the town hall's planning department.
House prices in Britain are totally out of proportion to the actual cost of building them, particularly where the developer only has to pay the architect for one design and then buys up some cheap farmland and puts up rows and rows of identical modern residences with fake Edwardian porticos (Don't they look nice? But the gardens behind them are hardly big enough to hang out the washing). It is no coincidence that many UK millionaires nowadays have Irish sounding names.

After the enormous world-wide fuel hikes in mid 2006, prices at the time of this posting (mid December 2006) had settled to around 1,300 to 1,550 Baht per cubic meter depending on the requested quality of cement to be used. CPAC is generally slightly more expensive (in our experience) in the cities than in rural areas. The supplier isn't actually making a vast net profit, for one thing, he is not buying the cement in loose bulk. He's ripping open 40Kg sacks just like you would be. The very large CPAC depots, the ones with twenty or thirty of their own trucks, will store their cement powder loose in a huge silo.

Everything else you need to know about CPA in Thailand is here http://www.cpac.co.th/

There is more about cement on Dozer's main page at http://www.coolthaihouse.com/infobasicmaterials.htm

And if you are still not convinced, this is the absolute bible, written and illustrated by professionals in away that EVERYONE can understand (it even includes calculators): http://www.pavingexpert.com/concmix1.html
No one can argue with it, not even here :D
Last edited by jazzman on Sun Mar 04, 2007 10:35 am, edited 3 times in total.
How to build a $20,000 / £14,000 house and a $???? MOTEL Updated 21 March 09 - with BOQ and costs
Don't let this happen in YOUR house.
jazzman
 
Posts: 2161
Joined: Wed Dec 06, 2006 9:11 pm
Location: Thailand

More concrete

Postby jazzman » Fri Feb 16, 2007 9:46 pm

Jazzman has been informed by a reliable source that these are the terms/numbers that the Thai industry understands for CPAC. These are the spec and prices which are practiced in civil engineering projects like bridges, flyovers, and for large buildings. It's probable that the average Thai house builder has never heard of them. It wouldn't surprize Jazzman whose builders haven't even heard of green gypsum board for use in damp places.

ABOVE GROUND FLOORS
180 Steng B1,530/cu m

ABOVE GROUND COLUMNS/BEAMS
210 Steng B1,580/cu

SWIMMING POOLS 1 - 2 m max. depth
240 Steng (includes waterproofing additive) B 1,690/cu

MAXIMUM STRENGTH ( strongly recommended for anything approaching 2 m average depth pools :
280 Steng B1,730/ cu

If anyone would care to shed even more light, please do.
How to build a $20,000 / £14,000 house and a $???? MOTEL Updated 21 March 09 - with BOQ and costs
Don't let this happen in YOUR house.
jazzman
 
Posts: 2161
Joined: Wed Dec 06, 2006 9:11 pm
Location: Thailand

Postby jazzman » Fri Feb 16, 2007 10:21 pm

The topic of CPAC now continues under this forum:
http://coolthaihouse.com/forum/viewtopic.php?t=672
jazzman
 
Posts: 2161
Joined: Wed Dec 06, 2006 9:11 pm
Location: Thailand


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