self build waterproof basement formwork membrane concrete

If you enter into a contract to pay and trust any team to build your basement for you, you are buying into the current, unreliable culture and you should expect your team to be unreliable at best and be out to cheat you mercilessly at worst.

Especially if you hire a main contractor who hires a sub contractor and leaves him to get on with it.
  self build basement

Seasoned professionals will all use steel threaded rods in a plastic sleeve. They leave the plastic sleeve as a hole through otherwise waterproof concrete; or else they fill the holes but some leak.

I was sent these images by a prospective client looking for a more reliable and trustworthy basement builder, so I don't know where he found them. He is planning a second basement and he says his first basement leaks - so perhaps this is it.

typical basement leaks

And here we see the hole destined to get the Delta-type sump for a pump, backup pump and backup power supply. All very expensive and not guaranteed to work either.

the sump in a basement

PLUS. HORROR !!!!    The pipes and ducts connecting the outside to the inside are underground not set in any waterproof concrete.

The shingle you can see in the photo above would have damaged the joints between sections of duct when it was tipped in. When the shingle fills up during a severe storm, water could flood in through these various duct joints far faster than the pump could pump it out. Pushing the drainage membrane off the wall, flooding the basement temporarily and leaving plasterboard, decoration and furnishings ruined.

No fancy warranty from a respected waterproofing company will cover any of this and all the 10 year latent defects insurers exclude waterproofing below ground.

These built-in errors are at the risk of the householder. No one else.

Sometimes you can't trust anyone. Whose fault is this? The architect, the engineer, the internal drainage supplier or the contractor. None of them seem to have realised the terrible mistake being made.

The client won't be happy.

Below are photos and my comments of work carried out by others in Hammersmith about 2007, Coventry about 2014, North London and Wimbledon about 2018. I had nothing to do with building any of them except Coventry where I had been approached for a quote but was not chosen.

They show how bad unsupervised concreting can be.

Following the Grenfell Tower fire, Dame Judith Hackitt reported to Government that the regulatory system, including building regulations, was not fit for purpose. She said "There is a need for a radical rethink of the whole system and how it works". " This is most definitely not just a question of the specification" ... , "but of an industry that has not reflected and learned for itself, nor looked to other sectors."

Final report, May 2018

"The current system is far too complex, it lacks clarity as to who is responsible for what, and there is inadequate regulatory oversight and enforcement.".
Click on this image to open a BBC News page from December 23rd 2020. Link to BBC Grenfell article

My point is simple. Your specifiers will try to specify an over-engineered solution to protect themselves from bad workmanship by the team you choose.

My grandiose, ahead-of-its-time, mind-blowing solution is to turn the clock back 40 years and choose a reliable team who accept the advice of a supervisor. This probably has to include you as project manager or team leader. You need the power and will to immediately send packing anyone who won't listen.

Back to the Hammersmith example:

After 8 years of losing tenants in this commercial office space, the landlords decided to do something about the ingress of water. They asked me to quote for repairs and by the time I arrived the walls had been stripped of plasterboard and the drainage membrane and we were looking at bare walls. The floor screed and floor drainage membrane underneath it were still in place. To be honest, I did not want the repair work. I just wanted photos of bad work by others.

basement sump This is a short video of the sump and the pumps that fail from time to time because of the massive workload.

It really does seem as if the contractor covered up the leaking concrete with drainage membrane having done nothing to improve the terrible work or reduce the leaks.

This water is from the River Thames. It came in relentlessly for many years and pumps switched on and off so often they switched on about five million times. No wonder so many pumps were replaced - but every change of pump took time and time meant a flood inches deep ruining everything.

leaking basement

leaking basement

The drainage membrane over the floor is still down, as well as any insulation and the floor screed over it.

We can see the water leaking above the floor screed. It is probably leaking through the kicker, through the kicker/wall joint and the wall concrete at the bottom where you can see the concrete did not get down to the bottom in good condition.

leaking basement

This is a concrete pile that was not covered over, as no doubt it should have been.

leaking basement

leaking basement

This commercial basement near Hammersmith leaked so badly that the pump switched on automatically every 40 seconds. Over 8 years that is about five million pump cycles so, unsurprisingly, the pump or the pipework failed every few months and every few months the basement flooded in under 10 minutes.

Coventry. Built about 2014.

This basement was built by a company who build with reinforced concrete all the time.

The first impression might be that it is nicely finished, straight and vertical.

basement repair

On closer inspection, there were many signs that while they could get away with bad workmanship they should take every opportunity. Frankly, they took advantage of their client; and this is the culture today. Construction companies take advantage of the firms the men work for, so the firms the men work for take advantage where they can from the construction companies.

Finding and using a technical advantage is obviously what drives an industry forward.

But learning not to tie the steel properly so it rusts at the surface, to not clean before you pour concrete, to not compact the concrete properly, to steal topsoil and replace it with rubbish you were paid to remove and to not complete the work you are paid to carry out is basically theft. But in legal circles it is called a construction dispute and there is nothing the client can do about it. That isn't to say there aren't clients who have learned how not to pay as well, creating a construction dispute of a different kind that the firm doing the work is powerless to overcome. Construction industry standards raced to the bottom years ago, so Grenfell was no surprise to the insiders who told Dame Judith Hackett "We knew something like this would happen". Or the brick walls blowing down in the wind from new school walls onto playgrounds, or scaffolding or tower cranes blowing down, or most architects, structural engineers, building control officers and insurers being convinced every new basement will leak.

Unless you employ the workers directly, perhaps on a cash weekly basis, so that you can get rid of anyone pulling the wool over your eyes, the examples on this page are what you should expect.

I succeed because I advertise for and employ locals who don't know how to do what I want. I show them, train them and supervise them. It works. You should let me do this for you as well.

In 2020 I was asked if I could stop it leaking and sort out other problems as well. I decided I would since Covid 19 might mean all work dries up at some point and I should build up my reserves at the bank.

The client stared at this thing unhappily every day. He could see water flowing in one corner of the pool continually where it is always below the water table.

bad basement workmanship fixing bad basement workmanship

The floor had been cast and a small kicker of stiff, old concrete formed on top to guide their wall formwork. A hydrophylic strip was fixed down on top of the kicker to stop any leak in the joint.

But, par for the course:
  1. The kicker concrete was not compacted and it leaked.

  2. Sand had been allowed to collect on top of the kicker so the wall concrete didn't even meet the kicker concrete (let alone bind on to it as it should have done).

  3. The hydrophylic strip got wet before the concrete arrived so it expanded early and tore itself off and was no longer in the joint.

  4. Not all the concrete in the bottom of the wall arrived at the bottom of the wall form in good condition. Some had lost so much grout coating the reinforcing steel all the way down that only stones arrived at the very bottom.
The thin layer of sand washed out and water leaked in ever since. Until I gunned out the poor concrete and replaced it with rapid-setting waterproof repair mortar and proper concrete once the flow of water was stopped completely.

They used polystyrene to block holes in their formwork but did not fix the missing concrete.

bad basement workmanship huge voids in concrete
They left reinforcing steel uncovered where they simply did not finish the job.

bad basement workmanship work not finished

They tied the steel badly so it was out of shape and did not get the required cover of concrete.

basement sub contractor no cover to steel
They left 400 holes they were supposed to fill. Waterproof concrete full of holes !
Note. My threaded rods don't leave holes.

basement sub contractor left 400 holes
They put the roof on this part during the winter. It got too dark so the crane couldn't lift the last beam into place. They just left it.

basement sub contractor did not finish

These faults are all in work they were paid to do properly.

The leaks were all fixed at an additional cost of about £8,000.

North London.

This basement was poured early during 2018. The sub-contractor just left it filling up with water. I was asked to carry out leak repairs before the structure advanced much further.

In fact, this was the last time I used resin injection.

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.

The point is, these issues are normal. The solution, as a rule, is not to improve workmanship but to install expensive internal drainage membrane, a sump, pump, backup pump and backup power supply to cover the leaks over and let them leak. But, as Hammersmith shows, if water is always getting in the day will come when a pipe joint or a pump will fail and the basement might flood before anyone realises.


This team was kicked off by the client, a chartered accountant, long before it could leak.

The main contractor employed a sub-contractor. I imagine a small team used to this kind of work but on major projects where there is always someone to ask.

They didn't ask anybody anything. No one came to help.

basement supervision

Other common problems I see are adding water to concrete and concrete too old. Sometimes both at once.

What I find remarkable is that professionals are so proud of their work in this next image they allowed publication.

The structural engineer has failed to meet his professional code of conduct specifying so much steel the concrete cannot get through unless an immense amount of water is added at site. Neither will a decent poker get through to compact it. The concrete has almost certainly segregated underneath the tight steel which means a lot of the cement is sitting on top of a lot of sand sitting on top of stones.

watery concrete and too much steel

In both these examples you can see that the excess water has washed vital cement out of the concrete.

wet concrete   tamping wet concrete

I was paid to observe an experienced contractor on behalf of the client. None of my products. No work by me. No supervision by me. Just observe and report.

The pump and the men arrived about 7.30am, but the work was far from ready and Hanson were put on hold - as it turned out for 4 hours.

The order was for 90 cubic metres and Hanson (who I presume had 12 trucks idle earning nothing for 4 hours) loaded 12 trucks as fast as they could and they all arrived one behind the other.

The last load was batched at 1236pm, arrived at 1345pm and was discharged by 1550pm.

Concrete is out of time after 2 hours. The technical explanation is that the 5% gypsum added to cement, that reacts with water quickest and seems to prevent the cement from reacting for 2 hours, wears off and the cement reacts with water and the concrete gets very stiff.

I doubt many men know about the gypsum. I know that every manager involved with concrete knows he shouldn't use concrete more than 2 hours old.

Yet this concrete flowed out of the truck after the driver recorded only 80 litres of extra water.
  1. Far more water must have been added while this truck was parked up 115 minutes round the corner, or else the concrete would not have come out of the drum.

  2. Even 80 litres of extra water jeopardises the water resistance of the concrete - extra water is not waterproof. This could no longer be waterproof concrete. The client did not get what he paid for, what he agreed to receive.
concrete trucks waiting   Note that the admixture is from Sika. Over the years every big cockup I heard about involved Sika. concrete waiting ticket

Looks like Hanson again here:

concrete trucks waiting oxford street

I had a phone call years ago from a man who said he was renting nearby while his house and basement were built but the Sika waterproof concrete had leaked. After a very long time Sika arranged for resin injection, but that did not work. After another very long time Sika arranged for their render to be applied. But that did not work.

In my experience, nothing slow setting can stop water getting in.

He complained that a big mortgage and continuing to pay rent to live elsewhere were ruining him. I had this story on this web site some years ago and a Sika employee phoned to complain. in fact, he said I had made it up. I gave him the phone number of the person who had called me (I hadn't recorded anything else). I didn't hear any more.

Another tale years ago involving Sika was a man whose West Country basement wall pour had gone very, very badly and he was basically ringing round for any assistance he could find to sue.

I took this video, Sika Water Resisting Admixture, sorry it's on its side, when I filmed the whole of this truck discharging near Brentwood in Essex. I had sold the client his polystyrene ICF formwork (that I stopped using about 6 years ago) so I was ready to add advice with filling it.

I mentioned above 5% gypsum added to cement to give 2 hours working time. But the gypsum has to have enough water or else it doesn't stop the cement beginning to react immediately.

I think that is what went wrong in the West Country and I am quite certain that is what had gone wrong in this video.
  1. The concrete arrived with the cement already soaking up all the available water. It was very stiff and would not pour out of the truck.

  2. As more water is added, more cement soaks up the water. The concrete does not get any runnier:
That is, until there is more water in the mix than all the cement could react with. This is about twice the water that should be the maximum water if the concrete is to be waterproof.

This poor driver emptied his own water supply into the concrete then he used a huge amount of water carried by the concrete pump. He had to try to wash the concrete down his chute with a hose. This was not the concrete supplier's deception in any way. At the batching plant they were probably asking where's the rep who is going to guide us?

The point here is that Sika will let you believe that their representative will be around on the day to manage the operation. But on none of these occasions did the site see anyone from Sika, and presumably neither did the batching plant.

Hanson won't deal with me and haven't for some years. That's OK because I think they short change customers more than the rest selling more air and less concrete in each cubic metre than they should. I check with pump operators from time to time if they have to wait for a bit more concrete to finish when Hanson are supplying and I think Hanson continue to be a lot worse than the others.

Who can you trust?


I will prevent all these problems as best I can which is usually completely.

Where I can't, when bad concrete turns up, I will refuse it if I have the grounds and it wouldn't jeopardise the work; or more likely I will do something sensible so it doesn't jeopardise the structure or the waterproofing.

Waterproof concrete is stronger than your structural engineer requires. If it is too wet it is probably still strong enough and if I can cover it with good, waterproof concrete a few minutes later with the next load all will be well.

But you have to have someone with the knowledge and the attitude that your best interests are what matter, or else your basement will leak and you will be forced to install internal drainage membrane, a sump, a pump, a backup pump and a backup power supply and hope the plumbing never fails.

This is my first wall pour with my powder-version powerful plasticiser in 2013. All my waterproof concrete ever since has looked like this.

basement expert concrete

The way to avoid all these issues is to build differently in the first place. The only way to build differently is with you involved yourself sacking anyone who doesn't do as they are told. On concreting days, I am the best person to have on your side showing your team how to do the work properly.

This might sound awful and absolutely not what you want. But you must not enter into a contract. You must employ the workforce and pay them yourself.

This might include a site manager who you pay as well. Fine. But keep turning up to inspect. Keep him working on your behalf. Don't let him change sides.

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