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Are basement leaks your fault? Probably.


Leaks in new basements are caused by poor workmanship and poor workmanship often starts in the design office. The more levels of defence against water ingress, the more each specialist team of installers can rely on another specialist team and cut corners themselves.

Result? Leaks. Why? Because the designer did not require anyone to do their work properly.

The UK’s Concrete Society set up a working party of 18 specialists, main contractors, academics and so on. They found that membranes had a limited life and that the simplest way to build a waterproof basement was with properly waterproof concrete and good workmanship, which most likely requires supervision.

Yet a building control officer was recently overheard saying that, when he worked for a water authority, it took months to stop all the leaks in brand new reinforced concrete water tanks – because the workmanship was always terrible.

The problem in the UK is that poor workmanship is more competitive than better workmanship and that is the fault of the design team*. It is all very well saying that as well as clay filled carpet or sticky back membrane that internal drainage, a sump, a pump, a backup pump, backup power and an alarm system will deal with leaks (often only after further repair), the client has lost a lot of money and valuable real estate and hundreds of people employed to do a good job have run away, paid well for a bad job.

*It is not the fault of the main contractor to choose a better sub contractor because it is in main contractors’ interests to have more materials and work specified rather than less.

Japanese companies build the most reliable cars (Which? 2014). They also invented the world’s most reliable concrete waterproofer. It is largely made in China now, so most of the world’s water resistant concrete is actually completely waterproof which may be why China builds so much below ground, for instance the world’s two largest underground railways.

Yet we don’t use this marvellous chemical in the UK. We never test concrete for water resistance. We pay outrageous prices for some soap, bitumen, polymer or a bit more cement in a pail or bag because each was once proven to make a tiny improvement to the water resistance of concrete, all falling far short of waterproof.

That means we buy products with a BBA certificate issued after a lab test rather than site-used concrete tested to BS EN 12390-8-2009, which is now the standard test for water permeability of concrete.

What we propose is that fully waterproof concrete, proven on each project to BS EN 12390-8-2009 is used for all underground structures and that at the tender stage the sub contractor knows that he will receive only fully waterproof concrete, and that what he does to or with the concrete to create leaks is down to him to repair.

If he wants tapes in the joints he can pay for them. If he wants others to put on membranes he can pay for them. If the basement needs internal drainage later he must pay for it.

If sub contractors know they must repair all the leaks, then those who stop causing leaks will become more competitive saving many thousands of pounds and months of work later.

Is this far-fetched? No. It happens with increasing regularity already in the UK. But only when the conditions were made clear before agreements were made. Is it costing more? No, it is costing far less. It might add a week to a month-long contract but when these basements are finished they are finished. Unlike most that are not waterproof till months later.

This basement in the Cotswolds was built by a team experienced at building basements for English Heritage (who insist on quality rather than speed).

That is why there is nothing in any joint (except scabbled and cleaned concrete) and the structure is waterproof from the concrete alone.

There is no honeycombing, no cracking, nothing can be seen that looks like it might need repair.

The client, a self-builder (and I.T. geek), project managed this basement for what most would believe is an impossibly low sum.

All specifiers should read the UK Concrete Society’s report “The influence of integral water-resisting admixtures on the durability of concrete”.

Some of their highly damaging comments are:

  1. “The BBA data are of limited value because the control concretes generally had higher water/cement ratios than the concretes containing admixtures.”
  2. “Overall, this study has highlighted the lack of suitable quantitative information to allow water-resisting admixtures per se to be specified with confidence.”
  3. or to allow meaningful comparison with “other currently accepted options for achieving durability, i.e. reducing water/cement ratio, increasing cement content, selection of cement type.”
  4. They quote published evidence, by a past director of the suppliers of Caltite, that Caltite simply does not work underground where it cannot be dried.

So why do specifiers believe that BBA certificated products add any value? It would seem to be because they believe the guarantees and the longer the guarantee the better. Caltite have one of the longest guarantees, so how does that work if they know full well that they did nothing to increase water-resistance selling their product?

Firstly they only guarantee the sound concrete. They may repair some leaks for big customers to keep them sweet, and wouldn’t you if you were making £millions selling some nonsense? But most leaks are repaired at extra cost. Who pays, we ask, if the sub contractor is long gone?

Secondly they specify a concrete mix equal to* the old C35A before BS 8007 was withdrawn (*equal in terms of total liquids to OPC). So they can quote from that BS that concrete properly delivered, placed and compacted will not visibly leak. Cementaid (UK) Ltd expressly does not guarantee leaks through cracks, voids, dirt etc., which are the causes of visible leaks through concrete.

However the Japanese chemical now made in Beijing makes a cement rich mix workable with much less water than any BBA certificated product. So whilst this very powerful water-reducer disappears when the concrete begins to set, the effect is that the very much denser concrete has no capillary network. Nothing can get through.

That is why we call JK-04 PL ‘Triple Proof’ in the UK. It Triple Proofs concrete against water, vapour and gas.

And we get proof at every project that absolutely, completely waterproof concrete was delivered. So clearly if there were ever any leaks it would be the fault of workmanship, either of design or on site, and only the culprit would pay not the client.




Sample certificates can be viewed here www.waterproofconcrete.co.uk/certificates.html

These basements, both by self builders, are completely dry from the concrete alone because all the concrete work was supervised. They both cost half any “specialist” quoted.

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