waterproof concrete

What is Waterproof concrete?
Why Waterproof concrete?
How to Waterproof concrete?
Should I Waterproof concrete?

In 2011, the new edition of a long-respected university text stated more clearly than ever before that completely waterproof concrete could be produced without admixtures.

"concrete with a low water/cement ratio ... make the capillaries discontinuous"
Neville, A.M. (2011). Properties of Concrete. 5th ed, p330. Harlow: Pearson Education.

In 2013, the UK's Concrete Society published a report by a working group of 18 members, experts in their fields, that states:

" water/cement ratio .... primary measure of water penetration and hence the durability of the concrete."
The influence of integral water-resisting admixtures on the durability of concrete. P36. Concrete Society. 2013.

Here is a photographed extract from my copy of "Advanced Concrete Technology", the volume called "Processes", the Chapter called "Concrete construction for liquid-retaining structures" by Tony Threlfall, 2003, Butterworth-Heinemann. Page 16.2.

It says that any permeability better than 50mm is good. You will see on the certificate for impermeability that our results in this case were 1, 1 and 3mm. We have dozens of similar results going back years, so we tend not to pay for this test (£600 plus VAT) any more. But you can specify tests if you wish.

  Click on this image to be able to read the text from the whole page.

from Processes, water retaining BS EN 12390 8
Without any proprietary additive a BBA product certificate is not appropriate. In the text you will see that the appropriate test is to BS EN 12390 part 8. In my work, I 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. I had 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 below to see two original test certificates.

concrete compressive strength report to BS EN 12390 3         concrete permeability report to BS EN 12390 8

It has long been accepted that good quality concrete with some extra cement as well as a little less water, such as C35A, is watertight. That is, no visible water will get through the sound concrete. But a network of capillary pores in the concrete could remain. They would suck in water for all time allowing vapour to dry off continually.

What the texts above are telling us is that concrete with extra sand and enough extra cement - but even less water than C35A - will be waterproof if made correctly because the pores with left over water between the original grains of cement will be closed off from each other instead of open between each neighbour continuously through the concrete.

It is now commonplace throughout Japan, China and South Korea to make concrete so dense no capillary network remains. All it takes is concrete improved on the lines of C35A and a more powerful water reducing plasticiser so that the good but ordinary concrete is made with less water - and it is waterproof.

Plasticisers in concrete disappear when the concrete sets (they actually decompose to carbon dioxide and water). As such they are not a constituent material of the hardened concrete so a BBA product certificate is completely inappropriate. BS EN sampling and testing is much more useful and revealing relating as it does to the concrete used in the project and not to something produced once in a lab.


Click on the image below to see all the BBA data plotted on our chart. Some data was missing, such as Caltite compressive strength test results, so we have made up missing data with our educated guess.

It proves how little difference all the water-resisting products make, compared to the huge difference that a better concrete mix design can make.

Opens in a new window.

chart BBA

Please note. The author acknowledges all the trademarks it mentions on this site.

The UK construction industry has got itself really confused.

It wants a BBA certificate for everything.

It wants waterproof concrete to come with a guarantee.

So suppliers have got BBA certificates for more cement in concrete and guarantees that the concrete will do what concrete does.

Some of them are selling little sachets of cement at 100 times the wholesale price.

And specifiers choose them because they don't read the small print.

Many of the BBA certificates have results from concrete far too stiff to use on site.

S1 concrete would have to be rejected or have water added before it could be pumped. Adding water on site would void any warranty, and void the BBA certification as well.

If specifiers read and understood the small print on many BBA certificates for water resisting admixtures they would realise that they cannot rely on the certificate because the concrete used on site will have to be different.

Some of the BBA certificates say order concrete with 0.40 wcr.

I have tried, pleaded with readymix concrete producers to sell me concrete with 0.40 wcr. But they say they just cannot mix it.

So I would also challenge admixture suppliers to prove that when they organise concrete with their additive in it that it only has the wcr stated on their BBA certificate.

I don't think they can so I don't think they will.

Click on the chart above to the right. It proves how little difference all the water-resisting products make, compared to the huge difference that a better concrete mix design can make.

Most of the guarantees offered are kept completely secret. The only one I have seen does not guarantee that the product will work, only that the concrete will do what the concrete will do anyway.

Caltite's guarantee, you will find one pictured on this web site, guarantees that if their product fails they will put things right (but only to the value of their product).

But what does their product do?

They seem to guarantee only the product but they promote 'the system'.

'The system' includes concrete with extra sand and cement and less water. So 'the system' will work because the concrete works.

But their guarantee seems to me to only be for their product. And I don't think that they tell you anywhere what to expect from their product.

So I don't think you could ever claim the product failed - even if you have leaks.

On site, they make the foreman sign a disclaimer saying the Caltite representative was not there to supervise and Caltite is not responsible for workmanship.

Most of the BBA certificate figures are for concrete that is too stiff to be used on site, so I argue that BBA certification is fraudulent.

This site argues that, in the light of BS8102 that requires internal drainage membrane as well as a prior defence that will substantially reduce (but is not required to completely prevent) water ingress, that paying a lot for a branded product that only slightly improves upon C35A is pointless, at least in domestic basement construction where every professional required to sign off a project insists on internal drainage as the second waterproofing measure.

Waterproof concrete and a substantial reduction in the amount of water that will get through a structure requires 3 things only

C35A concrete, PCE plasticiser and supervision.

Unfortunately, at the moment, the only way to get anything close to supervision is to buy a water-resisting admixture.

But you shouldn't be fooled that you will get supervision or by the bogus guarantees that come as well.

As far as the author is aware, in Japan, China and South Korea a plasticiser powerful enough to make concrete waterproof is the plasticiser of choice in most batching plants for most concrete because it also reduces the amount of cement needed for concrete to achieve a required structural strength. Therefore waterproof concrete in these markets is very normal, requires no other ingredient and costs pennies compared to the cost of admixtures in the UK.

In the Far East this chemical can cost contractors no more than £1 extra a cubic metre.

Author: Phil Sacre

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