waterproof concrete

What is Waterproof concrete?

  Waterproof concrete is concrete so dense the water-filled pores that remain are not connected but sealed off from each other.

This is achieved with a good blend of aggregates, extra cement and a powerful plasticiser, but no extra water.

The concrete must also be reinforced, poured, compacted and cured properly.

It does not need any proprietary admixture.


It is often thought that a BBA certified water-resisting admixture would make concrete waterproof.

But that assumption would be completely wrong.

BBA seems to charge a lot of money, considering it grants permission for the product to be used without having carried out meaningful assessment.

Just like the Grenfell Tower cladding. BBA did some testing but did not investigate whether most of these products would work on site.

Water resisting admixtures for concrete.
  1. BBA certificates don't prove that the product does anything of economic benefit to concrete used on site.

  2. Most BBA certificates are given because the permeability of a sample of concrete in a laboratory was reduced, no matter how slightly, by the admixture - but none claim to make concrete waterproof.

  3. Almost all the concrete tested was significantly different to the concrete that will have to be purchased by site.

  4. BBA has not, in most cases, tested or approved the admixture in a concrete mix that could be used on site.

    But specifiers and inspectors have insisted on products with a BBA without understanding any of the certificates in full.
Clients have simply had a lot of money wasted.
  Reynobond cladding panels.
  1. The Reynobond cladding BBA certificate states "Behaviour in relation to fire ... Class 0 surface in England and Wales, and a 'low risk' material in Scotland"

  2. It also states:
    "For resistance to fire, the performance of a wall incorporating the product, can only be determined by tests from a suitably accredited laboratory, and is not covered by this Certificate."

  3. Plainly, those responsible are those who accepted the BBA without reading that it still needed testing in the situation it was to be used.
That will be negligent.


The fact is:

British Standards

British Standards (these days amalgamated with Eurocodes) take a completely different approach.

British Standards are interested only in the concrete actually used in the project.

These days all concrete is supplied to BS EN 206-1.

In BS EN 206-1 concrete is considered to be water impermeable if, when tested according to BS EN 12390-8, the maximum water penetration is less than 50mm and mean average water penetration is less than 20mm.

Source: "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.

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

from Processes, water retaining BS EN 12390 8

All you need to have fully waterproof concrete is a good blend of aggregates, extra cement and less water (as a ratio by weight of cement).

That would normally be very stiff, so you need a very powerful plasticiser as well.

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


Phil Sacre

Basement Expert Ltd

01438 900303

07773 377087



The choice is between:
  1. BBA. Not proven to work but very expensive. Only really used in the UK and Middle East.

  2. BS EN. Proven to work and quite cheap. Used in the vast majority of waterproof concrete, particularly throughout Asia.
To make "2" above, the usual recipe is: CEM 1, P350, oversanded, target slump 60mm, the only additive is powerful plasticiser.

Our powerful plasticiser is usually added on site to save you money and it takes the 60mm slump to about 110mm, which is still very cohesive.

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.

The Concrete Society had the idea to plot the various data on BBA certificates onto one chart. I have plotted the same data here, as well as a few educated guesses where marked.

from Processes, water retaining BS EN 12390 8   Here I have plotted the before and after figures for compressive strength and water permeability from the BBA certificates I found for water-resisting admixtures for concrete.

What is striking is how varied the results for concrete without admixtures and how limited, in comparison, the benefit of a water-resisting admixture.

Some data was missing, such as Caltite compressive strength test results, so I have made up missing data with my educated guess.

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

The 'active' ingredient in Xypex, Krystol and Triton is only OPC. Cement. At about 100 times the usual cost.

If you click on the chart it will open in a new window so you can print it.

Have BBA conned you and not tested any of these concrete admixtures on site concrete?

To pump any concrete on site it needs a slump of at least 70mm. But the workforce would complain if the concrete was that stiff and add water (which would ruin any waterproofing and void any warranty) so concrete used on site needs a slump of at least 100mm.

But as this chart of data from the various BBA certificates shows, most brands seem to have cheated in the lab, proving that they did not test concrete that would be used on a building site.

These are the quoted figures on these brands' BBA certificates for the slump in the concrete with the admixture after 30 minutes, which is about how long a truck takes to batch, drive to site and manoeuvre into position. I have also put the cement content for each and for C35A.

Pudlo Sika BASF Xypex Kryton Krystol KIM C35A
45mm 40mm 135mm 35mm 45mm  
350kgs 350kgs 350kgs 325kgs 325kgs 325kgs

Reminder. BBA testing of Caltite did not make any concrete more resistant than a plain structural concrete, neither did they quote as many figures on their certificate as the other brands shown above.

I used to buy from BASF before I went to Asia and bought the best available there. In my opinion, the slump figure for BASF - the only one tested in concrete that could be used on site - supports the science that a quality plasticiser is all that needs adding to high quality concrete to make it waterproof.

Proving concrete is waterproof.

The overwhelming evidence: testing and acedemic; is that concrete is waterproofed with more cement, less water as a ratio and a very powerful plasticiser to make it workable.

The Standards state that concrete is impermeable if it passes testing to BS EN 12390 part 8, as defined in BS EN 206-1.

Nowhere do the Standards refer to BBA certification.

A BBA product certificate is only for a proprietary product. It is not appropriate for concrete. It is a permission to include that product. Not an endorsement that a product works: whether waterproofing concrete or protecting a tower block from fire.

I have had many successful tests for water permeability under pressure to BS EN 12390 part 8. Note: Many, many large sites routinely test concrete for compressive strength to BS EN 12390 part 3. This Standard is used thousands of times every day.

Part 8 is the test for 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 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 tiny spaces between the original grains of cement that contain the left over water 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. 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. But BBA certificates seem to be just permission to use something, and, as such, they are bought and paid for. Any testing seems to be just pretending to look compliant. Not assiduous. Tower block cladding could be a similar example, to water-resisting admixtures, of the BBA getting money for old rope.

The construction industry wants waterproof concrete to come with a guarantee.

So suppliers have got BBA product certificates when actually it is the extra cement in the concrete that did the business, and they provide guarantees that the concrete will do what concrete does.

Some of them are selling little bags 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.

When concrete is batched and water added, some of that water mixes with the 5% gypsum in the cement. The outcome is two hours working time with the cement.

I think that the reason many brands had concrete too stiff after 30 minutes is that their lab concrete did not have enough water to activate the gypsum. On site it is called a flash set.

I have had this problem myself, when I used to ask for 0.45 water to cement. Particularly in hot weather.

I changed that to 60mm slump, which will still be limited water but enough to activate the gypsum.

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.

Most of the guarantees offered are kept completely secret. The only one I have seen guarantees that the product will work but Cementaid don't say anywhere what the product does. So if anyone wanted to sue to get damages, because the concrete leaked, they must fail because they could not prove how the product: the Caltite, failed.

I have no reason to suppose that any of the others are any different.

When I put this point to engineers, they tell me they have specified Caltite hundreds of times without a problem.

There wouldn't be a problem because the concrete is made with extra cement and a low water cement ratio. No one has any evidence that Caltite waterproofs concrete (used underground in the UK) but hundreds of clients have had their build cost increased by £thousands for no discernible benefit.

Caltite's guarantee, you will find one pictured on this web site here, 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 don't say anywhere. Therefore no one could sue

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.

Specifiers seem led to believe that the Caltite rep on site supervises.

But on site the rep makes 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. It may prove to be the same for tower block cladding.

Most specifiers think that 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, just because a product has a BBA certificate.

We supply supervision and vibrating pokers that really work well for an extra cost. That way you know it will happen.

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