waterproof concrete

Waterproof Concrete. Certification and crack restriction - a guide for specifiers.

Following the Grenfell Tower disaster, it seems very likely to me that the culture of ticking a box just because a product has a BBA certificate will soon end in shame and huge lawsuits.

This page is about the BS EN alternative for waterproof concrete. Testing of concrete actually used on site will, I suspect, protect specifiers' reputations and PI far better - just as it already does for strength of concrete.

The reason I am comparing the fire disaster to waterproofing concrete is that the BBA for the cladding, here, is just as full of evidence that the cladding will not work or has not been tested for its proposed use as BBA certificates for water resisting admixtures (and hydrophylic strips and carpets as well).

In other words, if everyone had read and fully understood the cladding certificate (A selection of cuttings here) they would not have used it, neither would anyone specify a water resisting admixture for concrete if they fully understood each of the BBA certificates for them.

Time will tell whether it will be the specifiers or the BBA certification that will get the blame for the Grenfell Tower disaster. My money is on specifiers because BBA wrote the small print that the specifier didn't read.

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).

A condition on BBA certificates, both for the cladding and all water resisting admixtures, is "This certificate ... has to be read, considered and used as a whole document - it may be misleading and will be incomplete to be selective".

So if a certificate somewhere contains any warning, the specifier will be at fault for ignoring it.

Many BBA certificates for water resisting admixtures for concrete state clearly (but possibly in numbers hard to comprehend, Comparison chart here ) that many of these products either don't work or only make a very small difference.

Following the fire, there were immediate claims that the testing of the cladding panels fell short. Indeed the cladding was not fully tested by BBA.

waterproof concrete

This graphic is from the BBC News web pages.
This is clause 6.5 from the BBA certificate.

"6.5 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."

After the fire this will be shocking. Yet it is typical of BBA, who in similar fashion have not declared that any water resisting admixture makes concrete waterproof.

The BBA certificate for the panels reported to have been used is here. This certificate seems to give broad approval for fire risk, including the words "a 'low risk' material". And BBA seems to have done nothing following these panels being blamed for tower fires in France, the UAE and Australia.

BBA Certification of water-resisting admixtures.

Why am I comparing BBA certification of panels with certification of products like Caltite?

On other pages I have explained and backed up the UK's Concrete Society findings (2013) that BBA certification is low value at best.

For instance, academic studies of Caltite have proven that it does nothing of value in concrete used underground in Britain, such as perimeter walling for basements. Yet many specifiers continue to specify it because it has BBA and they never had a problem. NHBC accept it for the same reason, as does Building Control. As did building control accept the tower cladding.

I appreciate the issue is not one of safety or loss of life, but the Cementaid system works because the particular concrete mix that it is added to is waterproof anyway. The Caltite additive is just a waste of money. Clients' money. And after the Grenfell disaster clients are going to look to see if their money was wasted by specifiers relying solely on the existence of a BBA certificate in cases where the testing was woefully short of rigorous - which IS the case with Caltite since BBA only proved that concrete with the additive could ALMOST be as water-tight as a plain structural concrete.

The same might be said for bentonite clay-filled carpets that cannot be kept dry, in UK weather, from the time they are unpacked to the time they are backfilled against weeks later.

And bentonite clay rubber strips for joints between concrete elements. Far too often they expand after rain and tear themselves off the floor slab or kicker before the wall concrete arrives. Even those in cages that cost clients a lot of money.

All absolutely useless on site if it rains. Or if they are fitted wrongly. Or if the kicker beneath or the honeycombed concrete over the top will leak anyway.

But all continue to be specified because they have a BBA certificate.

BBA certificates state that products must be used as instructed by the supplier. They don't say, where perhaps they should, supplier instructions are impossible to follow in the muck and wet of a basement excavation.

waterproof concrete waterproof concrete waterproof concrete waterproof concrete waterproof concrete

Reliable certification of water resistant concrete.

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.

Obviously this testing is on concrete actually used on site, not sample concrete manipulated to improve results once in a lab.

So, surely, testing to BS ENs protects a specifier far better than a BBA certificate.

Here you see 3 test certificates from when I first started importing a powerful plasticiser for concrete. I followed concrete trucks till I got lucky with what they were carrying.

This was one of my customers.

The results are all zero penetration.

The powerful plasticiser that made this mix waterproof costs £23 per m³ today - including a unique guarantee that the workmanship will not leak.

Here the result is zero penetration.

The Pudlo cost about £40 per m³.

Pudlo was added to concrete already waterproof.
Everdure Caltite

Here the result is zero penetration.

The Caltite cost about £80 per m³.

Caltite was added to concrete already waterproof.

concrete permeability report to BS EN 12390 8 concrete permeability report to BS EN 12390 8 concrete permeability report to BS EN 12390 8

I give a personal guarantee that if I am paid to supervise, if my advice is followed and the products that I sell that make workmanship better are used, I will fix any visible ingress of water through concrete or joints. Pudlo keep their guarantee a strictly guarded secret. But it is definitely subject to terms that exclude workmanship and limited to the value of their materials sold.
You will find more detail in 'Others examined'.
Cementaid guarantee the System. The System includes a waterproof concrete mix. Nowhere do they seem to explain what to expect of Caltite so, presumably, no one could win at law claiming that Caltite failed.
You will find more detail in 'Others examined'.

What the client wants is no leaks. He wants better workmanship than the 5 photos above.

The secret of success is not a BBA certificate. It is SUPERVISION.

Cementaid do not supervise. They turn up and get the foreman to sign their disclaimer. Their guarantee repeats that they attended but did not supervise. When I watched the concrete delivery and took a sample of concrete, it was the sales rep who came from Cementaid. He noted we had a poker. Actually we had two but he hadn't looked properly.

Do Pudlo supervise? I was once told they employ boys off the street, and the only time I used them (because NHBC insisted) their "supervisor" could not give a toolbox talk to my team because he had been a scaffolder till the previous week. He didn't watch the pour. He came back later for concrete ticket numbers.

My point is simple. Specifying any BBA certified product could be wasting the client's money and if the certificate makes it plain, even if not in clear English, that the product doesn't justify its cost then, following future news programmes about the cause of the fire, clients might soon consider looking to you to get their money back for products proven not work, like Caltite. Or poor value, like Pudlo.

The Technical Section.

Crack control in waterproof concrete is essential.

Different parts of elements and elements of different size cool and shrink differently.

BS 8007 has formulae but seemingly only based upon CEM2 (flyash) concrete which gets less hot and gains strength slowly.

Waterproof concrete made with pure OPC, CEM1, gets relatively hot but is hardened before it gets a chance to cool.

Other sources of crack width calculation are
CIRIA, early-age thermal crack control in concrete, C660, CIRIA, London 2007. THE CONCRETE CENTRE. Concrete basements Guidance on the design and construction of in-situ concrete basement structures to the Eurocodes. MPA, London, 2012.

I am not a chartered engineer so I am going to give you the benefit of my experience to add to your professional learning, not tell you how to do your job.

Crack Protection.

This is typical of a crack where there is not enough distribution steel and the ends of the walls are restrained.

A 300mm thick wall with A393 and 12mm starter bars on 200mm centres in both faces will crack like this and may not fully heal, whereas the same steel in a 200mm thick wall seems to always heal completely.

If the starter bars completely restrain the bottom of the wall, the crack will not reach the bottom.

We want any crack to autogenously heal before we backfill, to heal before water could flow through and prevent the healing process.

More distribution bars and thicker starter bars seem to provide the solutions.

Note that I have never seen horizontal cracks, no doubt because the wall height can contract unrestrained on cooling.

I see very little cracking in slabs and almost none that does not self heal with only two layers of A393. Probably because slabs lose heat much more easily than walls still in formwork, so they do not get as hot. Also, they can probably pull the edges in since they are rarely restrained.

Caltite, I have been told, recommend more bars rather than thicker bars for crack control. It is not an authority but I have followed that advice with success.

Therefore specifying 12mm bars on 200mm centres may not be the best way of increasing distribution steel.

Two faces of A393 has always proved to be sufficient vertically (even though it is only 0.25%) but not horizontally in a 300mm thick wall. Two rows of 12mm starter bars are not always enough either.

I think it is better to fix extra 10mm distribution bars midway between the horizontal welded A393 bars, this means that 10mm distribution bars are on 100mm centres.

The A393 bars probably satisfy your structural needs and you will specify corner bars and bar laps as you see fit.

However these extra bars for crack restriction simply need to be in any crack and not slip, so we feel that at corners these bars just need to cross by 10mm and straight lengths lap by the minimum in BS 8110 which is 300mm.

  waterproof concrete crack width

Capping Bars.

Some engineers like to see capping bars all along the top of a wall and, sometimes, even a central distribution bar.

Concrete cannot be poured through a tube to the bottom or properly compacted with a vibrating poker with this amount of obstruction.

In contrast, we like to see the same bar Shape 21 on 1m centres both horizontally and vertically throughout the wall to control the space between the steel and keep it all perfectly upright throughout, not just along the top which would leave the middle to curl and wave without control.

Good Practice.

I have a number of rules worth following.

  1. Use good quality, cohesive concrete.

  2. Deliver it to within 1250mm of the bottom of where you are placing that concrete.

  3. Vibrate it properly. In, out slowly, every 200mm.

  4. Do not have to lift the poker more than 2m to move it along. That probably restricts formwork height to 2m each pour.

  5. Do not loosen or remove the formwork for 3 days.
If your project has enough labour and a supervisor to watch these 5 rules are applied, no concrete ought to visibly leak.
  basement construction   basement construction
basement construction

To have a kicker at the base of a wall or not?

Kickers are usually the height of a piece of timber readily available on site. 50mm, 75mm or 100mm.   The kicker concrete sinks into the slab during compaction if cast at the same time, or else concrete added later is not fully compacted because there is not enough there to poker properly.

I find it ironic that this photo of very poor practice, holding the poker in one place and clearly emptying the kicker with the vibrator so the kicker must get re-filled later with different concrete - is from a BBA certificate.
forming kicker tied to starter bars  
forming kicker   If you look up at almost any concrete frame under construction you will see voids beneath kickers. Kickers get cast later, often with poor, old concrete.   forming kicker

Therefore, in my experience, kickers always leak and the concrete needs replacing later since general porosity cannot be waterproofed by resin injection. Neither can you coat inside with water coming in pushing your remedy off before it cures. Any repair outside will get damaged during backfilling, because protection board is no match for a digger bucket.

However the Concrete Society stated, (The Structural Engineer, Vol 93, issue 1, Jan 2015, p48) "In liquid-tight construction, it is recommended that a kicker with a height of 150-250mm is constructed monolithically with the base slab. While kickerless construction may be preferred by some contractors in the interest of speed of construction, the associated additional risk of water penetration is not warranted in liquid-tight construction."

Unfortunately they do not explain any of their thinking,
and I cannot either. None of it makes sense to me. But then I spent most of my working life as the site engineer, not as a chartered engineer.

I did ask one structural engineer who thought the benefit of a kicker was to clamp the formwork on tight and reduce grout loss.

I use spray foam to reduce grout loss.
  preventing grout loss with spray foam

  1. Monolithically.
    This can normally mean at the same time or later with a scabbled joint.

    At the same time with the same quality of workmanship as the slab itself is largely impossible. The kicker must be filled and compacted when the slab has stiffened yet before the two concretes can no longer be mixed, else there could be laitance through the joint that will leak.

    Later is no different to forming the walls themselves later. The deliberate construction joint needs to be sealed.

  2. Why should kickerless construction be preferred in the interest of speed of construction?

    Not using kickers is definitely more time consuming for me, considerably more. I save by not having to carry out repairs.

The kickers in the first photo is the usual method. Bits of timber, some nails and wire. Forming a kicker is rarely time-consuming.
  1. I have pages about kickers and joints.

    The "risk" comes from having a kicker, not from not having one.
Perhaps someone responsible for the article in the Structural Engineer will let me know the arguments behind their advice.

On my Joints page, in the Top Tips section, I discuss what I think is the best strip to have in a joint. If a kicker is demanded then this joint strip should be tall enough to start on the floor slab steel mesh and extend through the kicker into the wall proper.

To have a tape or strip in a joint or not?

The Concrete Society stated, (The Structural Engineer, Vol 93, issue 1, Jan 2015, p47) It is good practice to protect all joints by incorporating water bars.

The accompanying sketch in the journal is of a preformed PVC strip backstop water bar.

These products need proper care to form and weld them the correct dimensions and monolithically around a slab wall joint. Unfortunately, a few mm too long and they sag and flop and tend to get smothered by wall concrete and buried in the concrete instead of remaining up the side where they would work. The Fosroc Rearguard products are of this type.

Without supervision most workforces will see a joint strip as a good reason not to do their work properly.

My own Supervision concentrates on getting the concreting carried out properly ignoring the strip.

Such strips overcome small errors and have value in a robust design. But they cannot overcome wholesale bad workmanship or very little care.


Does your idea of a guarantee really exist anywhere? Are you hoodwinked?

The first question I have usually been asked by architects and engineers has usually been "How long is your guarantee?"

And they seem to mean, against leaks.

But a waterproof concrete mix cannot leak. It is dirt, cracks and voids that visibly leak and a capillary network that lets in damp. And no BBA certified water resisting admixture supplier seems to guarantee against those.

Caltite (that doesn't work), Pudlo (that is mostly a little microsilica) and Sika (that is mostly a plasticiser) have all, so we have heard, carried out some repairs (some quite expensive). But they did not sign any work off until they inspected and found no leaks first. In other words, they like leak repairs that are paid for. They don't pay for many themselves.

Here on the right is Kryton's Technical Data Sheet web page for Krystol Internal Membrane. If you look at the very bottom you will see Warranty, which I have reproduced here, large enough to read. waterproof concrete guarantee

This Caltite guarantee was new in 2015.

It guarantees the System, not the Caltite.

The System includes a waterproof concrete mix: P350 and reduced water.

Cementaid guarantee only that concrete will do what concrete does.

Bear in mind, academic evidence states that Caltite does not work beneath ground.

Note in the guarantee that their representative did not supervise.

In paragraph 2.4 the guarantee states that Cementaid will rectify concrete through which water is migrating, but elsewhere all the reasons water would migrate through waterproof concrete are expressly excluded.

Leaving nothing Cementaid could be held liable for.

caltite cementaid
  waterproof concrete guarantee

Supervision is beneficial.

Is there really any point, and is it justifiable, to make your client pay for a useless additive so someone watches the concrete pour but absolves themselves of supervision or responsibility?

My guarantee may not be seen as robust. But at least I guarantee something.

And because I charge a separate amount for supervision, it takes place, properly, throughout.