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.

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 will remain. It will suck in water for all time allowing vapour to dry off continually.

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.

The authoritative test for waterproof concrete is BS EN 12390-8:2009. Testing Hardened Concrete part B: Depth of Penetration of Water Under Pressure.

ESG in Uxbridge performs this test.

Plasticisers in concrete disappear when the concrete sets. 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.

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.

Click on the chart to 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.

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


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

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