self build waterproof basement formwork membrane concrete waterproofing

Properly waterproof concrete never fails.

It needs to have been designed, made, jointed, delivered, poured, compacted and cured properly - all of which is quite easy when everyone is focused and supervised where supervision helps.

Or else you will have waterproof concrete but with cracks and voids that leak.
  1. It is very common for contractors to use hired in formwork that makes perfect workmanship impossible. Plus,they leave holes through waterproof concrete walls and their kickers leak incurably.

  2. And the people installing anything else might see on the drawings that theirs is not the only defence against ingress of water, so they can cut corners because the other one should work.

  3. Any other defence they install may not be up to the job and shouldn't have been chosen.

  4. The defence would never work anyway.

  5. No one checked the BBA certificate to see if was proven to work in this situation.

  6. No one supervised the work.

  7. And anything other than waterproof concrete is likely to get damaged by someone who hides what they did.

Those waterproofing things that would never work anyway.
  1. Sticky back membrane.

  2. Clay filled carpet on the outside of a wall.

  3. Swelling strips in joints.

Normal practices that leak.
  1. Kickers.

  2. Filling a wall to full height in one go.

  3. Dywidag threaded rods and plastic sleeves.

  4. Lots of vertical joints.

  5. Not building to properly avoid all forms of cracks.
If you cannot find why on this web site, try looking on
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5. BBA certificates.

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).

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.
My point is, If you think you will get success because your specifier insisted on products with a BBA certificate, prepare to be very disappointed with the result and how little money you have left in the bank.

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.

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.

External Drainage.

External drainage to a soakaway can backup water in very wet weather and actually deliver more water to the outside of your basement than if you didn't have it.

If your other defences aren't up to scratch, your basement will be wet during heavy storms.

Where external drainage will always work by gravity, it is a no-brainer. But where it is doubtful whether it will always work it should probably be avoided.

Sometimes internal drainage membrane is not up to the job.

Internal Drainage. The specifiers' favourite.

Sometimes the leaks that the membrane and pumps deal with are so severe that eventually the pump or the pipes will break down and the basement can flood.

The people who installed it won't be interested in your claim if it isn't a fault with their workmanship. They will tell you to talk to your insurer.

The people who insure the installation won't be interested in your claim. They don't cover the pump or pipes.

Your warranty provider won't be interested in your claim. He doesn't include below ground waterproofing in your cover.

Any damage by flooding is the householder's problem unless he has household insurance that covers damage by a pump failure.

So, please avoid relying on internal drainage.

Even if the architect hasn't specified any kind of water resistant concrete, if this is your house make sure you include it. No one in authority will refuse you permission to use C35A. My concrete is C35A with a bit more cement, a bit less water and a powerful plasticiser to allow a stiff mix to be compacted properly. If your engineer is happy to put C35A (or C40A) on your drawings, you can get me to help you exceed the C40 and exceed the A for aqueous for less money than any proprietary brand.

This is what I do.

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