self build basement formwork membrane concrete waterproof

Basement concrete should be as water resistant as possible and poured, laid and cured as well as possible because
  1. There is every chance it will be waterproof

  2. No one will damage it, unlike every other way of waterproofing

  3. The extra cost of doing something properly is less than the cost of doing something badly then something else as well.
  self build basement

But your waterproofing specifiers and inspectors - whether your architect or your engineer, building control or warranty provider - are all trained and instructed to assume that your concreting will be terrible and your concrete full of leaks.

That's why they all absolutely insist on ignoring what your concrete might do and insist instead on very, very expensive internal drainage that, so they think, can be repaired from the inside even after the new dwelling is occupied.

The other major issue is that they all want to protect themselves in the laziest way possible which is to insist that everything you use has a BBA certificate. Unfortunately they specify a lot of crap that costs a great deal of money because BBA certification is a process that seems to be rotten to the core.

Your job is to prove them wrong and to get your way.

But you have to go along with them until you prove them wrong, and unfortunately your first chance to prove that your concreting work was carried out well isn't until
  • You have your roof on and windows in

  • Your structure completely weatherproof

  • Your basement pumped clear of all the rainwater that collected in it, cleaned and dehumidified

  • And you have just had some heavy rain.

Don't worry if you do these 4 things and you discover some leaks because they are easily repaired while you still have access to bare concrete.

If you buy my products and supervision I can guarantee your basement and repair any leaks FOC.

I have other pages about doing your concreting well: how to fill walls, kickers and joints.

From this point forward, this is similar to the text on the pages for architects and engineers to read.

If you can understand why the professional team are all so dogmatic, you can pick your way through the maze. I did so dozens of times.

For architects and engineers:
  1. Why paying for any big-name brand, such as Caltite or Sika, is a waste of clients' money.

  2. The truth about waterproof concrete.

Why paying for any big-name brand, such as Caltite or Sika, is a waste of clients' money.

After Grenfell clients will look to specifiers to get wasted money back if they learn that the BBA certificate the specifier relied upon (but did not read) provides the evidence that these products don't do anything of value.

At the moment specifiers and inspectors don't fully understand these certificates because they don't read them in full. But I think they soon will because a Grenfell enquiry will condemn this practice as negligent. At the moment, most specifiers and inspectors just tick a box if a product has BBA. No further questions or research.

It is concrete that can be made waterproof. There is not any admixture that waterproofs un-waterproof concrete used below ground for basement construction.

BBA certification is completely inappropriate, being little more than a licence for the supplier to print money if he invests in some meaningless testing by BBA.

Do all products have to have a BBA certificate or else they cannot be used? (Not according to a statement here from the BBA web site 22 Oct 17 stating that a specifier needs to make a judgement, not just trust a product because it has a certificate).

On November 9th 2020 the Grenfell Tower enquiry was told "This reveals an industry in which Arconic, Celotex and Kingspan were content to push hazardous products into the marketplace and sought to market them dishonestly. These products should have been safe, they should have been tested and certified rigorously, and they should have been marketed in an honest and transparent fashion. None of that happened. The testing and certifying bodies, such as the BRE and the BBA, were quite happy to go along with this process."
(Source: Click on the linked text above, opens in a new tab).

ABI exposes the 'utter inadequacy' of the laboratory tests currently used to check and certify the fire safety of building materials. 25th April 2018.

On 26 February 2021, this article reported on a technician involved with fire testing the products used on the Grenfell Tower.
  1. He failed to notice in 2014 that a test rig for an insulation product from Celotex had been secretly altered to increase its chances of passing.

  2. He claimed that manufacturers could sneak extra components onto test rigs without inspectors knowing

  3. The reliance was very much on the honesty of the client.

  4. If you have got somebody who is going out of their way to deceive, then there was a possibility they could do that, if that was their intention.

What BS 8102 says about waterproofing a domestic basement.

Bear in mind, BS8102 treats cellar conversions and new build basements with the same solution. But a new basement can be built to be dry whereas Victorian cellars were allowed to be damp because they were only for storing coal, not living in.
  1. Two defences, different types from
    1. External
    2. Integral
    3. Internal
  2. The first should substantially reduce the amount of water that gets through that the second defence will have to deal with.
I am telling my customers that they can have a completely waterproof structure from the concrete alone. But the specifier does not need to worry that a completely waterproof structure will be achieved.

The specifier needs only to know that if completely waterproof concrete is the target, then substantially reduced water ingress will be achieved. The specifier does not need to worry about any brand of anything with a BBA certificate because concrete is inherently water resistant anyway.

At the design stage, the specifier simply notes on the drawing
  1. First defence, water-resistant concrete, C35A or better. Ideally all workmanship supervised.
  2. Second defence Internal Drainage System by Approved Supplier.
If the customer thinks that he built the basement completely waterproof from the concrete alone, he can invite the specifier, building control and his insurer back
and if you are all happy that there will never be a drop of water to pump you can agree on just a vapour barrier of waterproof paint or polythene instead.

If, after inspection, you still insist on internal drainage, then if you did not see any water to pump it needn't be the £40,000 from Delta or Newton. I'm sure you could agree something cheaper with your client.
My point: BBA certificates say these brands may be used. They do not say these brands work. In my view, BBA "goes along" with those paying its fees to pretend expensive products do something of value, and perhaps this is true of everything with a BBA certificate. BEWARE if you specify relying on a BBA certificate and the word of a salesman.

My evidence is from The UK's Concrete Society report 2013* as well as BBA certificates.

The proper certification for waterproof concrete is concrete made to BS EN 206-1, and concrete tested to BS EN 12390: testing of hardened concrete.

Thousands of test cubes are tested to BS EN 12390 part 3 every week. This is the test for compressive strength.

BS EN 12390 part 8 is the test for depth of penetration of water under pressure.

The different parts of BS EN 12390 are listed here on the BSI web site.

I have a page with all the concrete waterproofing science explained here

The cladding and insulation for the Grenfell Tower both have BBA certificates. The insulation certificate got taken down. The cladding certificate 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."

How could the cladding have been allowed? Unless everyone in authority saw it had BBA and the certificate, alone (unread and not understood), ticked their box?

BBA certificates for water-resisting admixtures for concrete are just as bad.

Caltite's does not prove it makes concrete any more water resistant than a structural concrete without it.

Sika's improvement is barely measurable.

Most of the rest might at first appear to have made a small improvement but, actually, the small improvements can be explained by a reduction in water cement ratio* rather than any clever chemical.

All this from analysing the various BBA certificates*.

For years I have always used the concrete mix that is proven to always be completely impermeable. Without any proprietary admixture not proven to do anything but cost a lot of money.

A working group of the UK's Concrete Society published a report in 2013* produced by consultant engineers, academics and other experts. They strongly suspect that it is always the concrete that will be waterproof, not any of the admixtures.

But to make matters worse, most of the BBA tests were on concrete samples that would have been too stiff to pump. On concrete that would have to be rejected on site or, more likely, have more water added which defeats the purpose of trying to waterproof concrete.
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.   Click on this image to be able to read the text from the whole page.   from Processes, water retaining BS EN 12390 8
It says that permeability better than 20mm is satisfactory. You will see on my certificate of permeability that my results in this case were 1mm, 1mm and 3mm. I have dozens of similar results going back years, so I tend not to pay for this test (£600 plus VAT) any more. But you can specify tests if you wish.

Every BBA certificate for a water-resisting admixture for concrete tells the user to buy an already water-resistant mix of concrete. This is 325 to 350kg of cement per cubic metre with reduced water.

C35A in BS 8007 is a concrete mix with 325kg of OPC and 55% water by weight of cement and this is a watertight mix.

In the text you will see that the appropriate test for waterproof concrete is to BS EN 12390 part 8. There is no mention that a BBA certificate will prove concrete won't leak.

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 the left to see two original test certificates.
  I always buy concrete over-sanded, with 350kgs of OPC and water a maximum 50% by weight.

The concrete chemistry books state that by adding a little more cement to C35A and reducing the water a little further that pores of water between remnants of cement grains will be closed off from neighbours by crystals of hydrated cement.

However such a mix would be too stiff to pump or compact without a more powerful plasticiser than those usually available.

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

* 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 authors of this report had the bright idea of plotting all the BBA data on to one chart. Here is the same data plotted on to a chart I produced. It includes my educated guesses where data is missing, see the legend to see which.

chart   Concrete needs to be the right consistency to be pumped into formwork and compacted properly without bleeding. 120mm to 140mm slump would be fairly usual.

So any BBA testing on much drier, stiffer concrete has not tested concrete that would be used on site. Site concrete would have to have more water, which would massively affect test results.

Seemingly, a very similar situation to Grenfell Tower cladding. The cladding resisted a flame in a lab but they (BBA) stated that they didn't know if it would work on a tower, on the certificate.

That is what the cladding BBA certificate states and every admixture certificate also warns that BBA didn't really find out if any of the admixtures would work on site.

Slumps of tested concrete
Pudlo 45mm
Sika 40mm
Xypex 35mm
Kryton KIM 45mm
Caltite no information
BASF 135mm. Hooray. Site concrete. But BASF performed very badly.
Only BASF has a certificate for concrete with the consistency used on site.

All these admixtures have to include a water-reducing plasticiser.

Apart from plasticiser what seems to be in them?

With a little more cement or cement replacement:
Krystol KIM

With liquid plastic absolutely useless below ground where it won't dry
Others with polymer.

There is no evidence anywhere that anything other than extra cement and less water can waterproof concrete used beneath ground where it won't dry. The concrete will need a particularly powerful plasticiser as well to make it workable.

If you specify any of the famous brands, you risk litigation after Grenfell enquiries rule that not reading and fully understanding a BBA certificate is negligent.

None of the BBA certificates provide any evidence that any of these products make enough difference to site concrete to be worth any money at all.

The proper procedure is to specify concrete made to BS EN 206-1, and concrete tested to BS EN 12390:8 permeability of hardened concrete.

Basements are usually waterproofed to BS 8102.

Two defences against ingress of water.

One must substantially reduce the amount of water the second has to deal with.

This concrete and my work is always absolutely waterproof.

  1. I use waterproof concrete.

  2. I cast fibreglass threaded rods in walls instead of leaving holes through plastic tubes.

  3. I pour walls to only half height or so. This means I get concrete down to the bottom in better (perfect) condition and I can poker the concrete right at the bottom properly.

  4. I don't use kickers. Kickers are impossible to form to be waterproof.

  5. All joints were waterproof to BS 8007 (instead of using swellable strips or carpets that swell before the concrete is poured and don't overcome poor workmanship anyway).

  6. I train my own workers. I don't use experienced workers experienced at doing the work badly.

  7. I supervise all our concreting.
I am telling your client that he can do the same, or at least do a lot better than usual if he tries to do his work well rather than just doing all the work the usual, slapdash, corner-cutting way.

If you have external drainage, our concrete won't face any pressure.

If you have internal drainage, the pump should never switch on - which gives great confidence that it won't break down at a bad time.

If you specify a BBA certified waterproof concrete, hydrophylic strips and internal drainage with a sump, pump and so on, there is no guarantee that the work won't be carried out badly.

This basement was poured early during 2018. I was asked to carry out leak repairs before the structure advanced much further.

leaking basement repair This short video was taken by and sent to me by the house owner.

He told me that they used a water resistant concrete from Cemex and the Fosroc hydrophylic joint strip that Cemex recommended.

But water is pouring through this corner.

Before the owner contacted me he had made matters slightly worse by putting shingle behind the leak before he backfilled, which will be delivering more water even faster.

Obviously the reinforcing steel or the shutter were in the wrong place because there should be concrete covering the steel reinforcement.

It would be my guess that the hydrophylic strip had already fully swollen, far too early, before the wall concrete was poured. When the team failed to compact the concrete properly around the hydrophylic strip it was unable to expand any further. Completely useless and a waste of money.

Frankly, these leaks are due to poor workmanship in turn due to no supervision.

Back to writing for the self builder.

Firstly, I have tried to explain to you and your professional team that using a BBA certified additive in concrete only wastes your money.

Secondly, building the basement structure with concrete, not waterproof but doing the work well, will satisfy one defence according to BS 8102. It will reduce the amount of water that comes in compared to that if worse concrete was used more badly, for instance concrete blocks and a cavity loosely filled with concrete.

So your specifiers should leave you alone to do the concreting as well as you can. You need to obey the structural design. You should not need to pay for crap.

It is expensive at £600 plus VAT, but consider getting your own certificate to prove the concrete you used is impermeable. If you buy my powerful plasticer from me and put it into the stiff but already-waterproof mix I tell you to buy, it will pass the test easily.

test certificate waterproof concrete

The result needs to be less than 20mm to be a pass.

If you did a good job, then before internal drainage needs to be installed and paid for you can prove that it is far too over the top and your second defence needs only be a vapour barrier, not a pumping system.

I have to emphasise that you have to prove you DID a good job. All your professional team is trained to believe you WILL do your work badly.

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