Admixtures for concrete.
We can sell you an admixture that makes concrete waterproof.
We don't go into the science here. You can read all the science on this discussion web site.
As good as any of the rest out there.
For less money.
£40 a m³ if we come to you, supervise and guarantee your structure will not leak. Concrete or joints.
£13.50 a m³ if you buy it and put it in yourself.
This page is in 4 parts Click on these links to go straight to the part you want to read.
You need this to get good joints between different loads of concrete.
Each dose to add to the last 0.5m³, £4.50. To avoid problems like this.
The admixture for readymix concrete can only go in drum trucks that carry concrete batched back at the batching plant. I cannot waterproof volumetric mixer concrete. Neither can anyone else unless they got a truck specially adapted to suit a particular chemical.
Powder to make drum-delivered readymix concrete* waterproof.
£40 per m³ is about the same price as other admixtures but our service is a 100 times better because we guarantee your workmanship if you followed our advice. No one else does, they only guarantee their chemical to the value of their chemical - even if they attend site and watch.
We come to you, we put the admixture in the concrete*, we supervise your team as best we can. If they listen and do as they are told we guarantee the structure created to be free of visible water ingress. Else we will repair leaks FOC.
Price £40 per m³ plus VAT**.
We send you the powder and you put it in*.
Price £13.50 per m³ plus delivery and VAT.
They would also get you to spend a lot of money on something to go in the joints. If your workmanship is bad these extras don't work anyway. If your workmanship is good you don't need them. So listening to us and doing as we say will save you money as well as avoid leaks.
£13.50 per m³ is 3 times better because you are getting the same concrete outcome for a third of the price.
Making readymix delivered in large trucks waterproof.
* The concrete purchased must be the mix we prescribe.
over sanded for pumping
target slump before additive 60mm
no other additives
Tell your readymix supplier that you will be adding and mixing in your own super plasticiser when the concrete arrives.
If you are asked, don't open a can of worms about Health and Safety unnecessarily, this will be done for you by the pump operator who will toss the sachets in from the back of his pump truck.
** Subject to minimum amounts per visit, depending on travel distance. Give us a call, number at the bottom of this page.
We have lots of other information on our basement building web site:
Basement Expert Ltd
It is the concrete that will be waterproof, not the admixture. As such a BBA product certificate is not appropriate and we do not have one. However we have had many successful tests for water permeability under pressure.
Many, many large sites routinely test concrete for strength to BS EN 12390 part 3.
We get concrete tested to BS EN 12390 part 8 as well. Depth of penetration of water under pressure on concrete. The pressure is equivalent to a depth under water of 30m and the pressure is maintained for 96 hours.
Click on either image to the left to see two original test certificates.
If you buy the sachets of powder to put in yourself, you need to know that each sachet is sufficient for 2 cubic metres of concrete.
You need to mix the powder for 6 revolutions per cubic metre.
So, if you have 8 cubic metres in a truck you need to add 4 sachets and mix them in for 48 revolutions.
You must count the revolutions yourself because you cannot trust anyone else to insist that the mixing is done properly.
Proper mixing is essential, or else you will get some concrete with too much additive that will be too runny and the pressure of the pump will push the liquid forward and leave the stones dry, and stuck very firmly indeed, in the pipes. Dismantling all the pump's pipes to clear many metres of blockage will cost you a lot of money. Perhaps £4,000.
When the driver complains about cost of diesel, look him straight in the eye and tell him you have paid for mixing. Tell him to mix it or take it away.
If the concrete is still fairly stiff, add a tiny bit of water. Don't listen to driver. Only add 5 litres. Mix about 10 revolutions. Once there is enough water the concrete will pour over the drum fins instead of breaking apart. That is when it is ready to use.
You should not be persuaded to add even more water to make the concrete even runnier because then you will lose essential grout out of gaps in your formwork and the concrete won't be waterproof. You need all the sand and cement to get the required density. (Don't worry about a thin dribble, but worry about losing half a shovel full.)
Mixing concrete on site and making it waterproof.
£10 for enough additive to make at least 1m³ of concrete on site. You will be supplied with a measure with your order.
You will need to make some gauges. I use two buckets for the ballast and a pot for the sharp sand. I cut bags of cement in half with a hand saw.
A typical batch will be
30 litres of ballast
2 litres of sharp sand
half a bag of cement
start with 2 litres of water
correct dose of liquid admixture purchase.
You will get instructions and a measure with your liquid admixture.
Add more water very slowly until the concrete flows, but is not runny, in the mixer.
Mixing concrete by hand is very expensive compared to full loads of readymix. You should probably only mix by hand where readymix would be too much at once unless you paid a lot extra for a small delivery or extra time on site.
There is no need to buy retarder for hand mixed concrete.
Wash the mixer every hour so that it is easy to keep clean.
Pump-Save Retarder. £4.50 a dose.
We could have called it "Cold Joint Preventer" instead. But getting soild concrete out of a pump pipe is worse than chiselling out a joint and refilling it. So it is called Pump-Save Retarder even though it prevents cold joints as well.
Concrete is the result of water and cement being mixed. After about 2 hours water merges with the surface of the cement grains and the mix becomes very stiff. Some hours later the merged parts form gel and by the evening crystals are forming from the gel, releasing excess water to merge with more cement, and so on.
Waterproof concrete has more cement and less water than usual, so it gets to the stage where it is too stiff to move sooner.
The concrete arrives stiff. The admixture is mixed in and the concrete flows. The pump hopper gets filled and the concrete is pumped until the truck is empty. When the delivery truck pulls away it leaves the hopper and the pipes to the top full of concrete - that sets where it is if it is there long enough.
Concrete setting in pipes takes a lot of getting out. The extra bits of line can be cleaned with a jet washer and rodding them with steel. It might take an hour but they can be cleaned. But to clean the pipes up in the air they have to be taken off back at the yard and the concrete pushed out with a hydraulic ram. This takes a couple of days so the penalty charge is big.
If the pump is completely bunged up and more concrete arrives, you will have to pay for that concrete but send it back because you cannot pump it. That means you will have to pay up to twice as much again for its disposal.
It doesn't usually get to that. But somewhere in between is common. If the concrete in the pump had the water added back at the plant more than 2 hours before the next truck arrives, it will probably pump out. But it won't compact. And where it won't compact it will leak.
Concrete does not arrive two hours old and you can get most of the concrete in and compacted with time to spare, usually. It is the last half cubic metre or so that sits in the pump's hopper and throughout its pipe system that gets to be two hours old sometimes before new concrete arrives and pushes it through.
So it all depends on when the next truck arrives - and that is out of your control.
But I hear you say, "if this is so common why haven't I heard about this before?" Because in the real world the pump operator or the workforce add water to the concrete in the pump hopper and circulate it through the pipes as soon as they realise there is a delay. In that way they keep the concrete liquid and they get good looking joints without blocking the pipes.
But extra water pushes the grains of cement further apart. Google 'effects of too much water in concrete' for yourself and these are what you will find.
These are problems no one can see while the workforce is still on site. The concrete will look fine for several months at least.
The concrete cannot become waterproof. Instead it will be porous.
More water makes the concrete weaker.
After a few years the concrete will crack (so presumably leak).
The concrete could segregate. That means the stones and the cement end up in different places and the stones have no glue.
But if it is going to be your basement, or if you will sell it with a 10 year guarantee, you will be responsible for poor workmanship, not your insurer.
The simple solution is to add a sachet of Pump-Save Retarder to the last half cubic metre of concrete in the delivery truck to give that concrete another couple of hours or so before it begins to set. With no harm to the concrete at all.
Keep tapping the drum and when there is about half a cubic metre left inside it, stop the discharge, toss in a bag of retarder and mix it 6 revolutions.
Carry on using the concrete. If you timed the retarder just right the concrete left in the pump will not go stiff for another couple of hours at least.
Important note. The retarder can only work if the concrete is still runny. If you are discharging the concrete very slowly you might need to retard much more concrete. In average weather add the retarder after less than 2 hours from when the concrete was batched. Sooner in hot weather.
It might be wise to buy twice as many doses as truck deliveries you expect, so that you have some spare doses in case one load is being discharged very slowly and you need to retard a lot more than half a cubic metre.
Please don't be afraid of paying me to attend your site when you concrete. Experienced people are not experienced at using concrete that is really quite different, because they have much less time than they are used to. Inexperienced people get it all wrong. Save money later by making me responsible for any leaks - and I will make sure you don't have any.
This is a very recent job where they thought they could do it without me. They have leaks everywhere. Not through the concrete but through all the gaps and bad joints.
It should not look like that, it should look like this. The difference is only that I was there supervising.