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HOW WE SAVE YOU A LOT OF MONEY
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First, a list of what you could spend your money on;
then the list of what we supply;
then a list of our competitors, what they say about themselves and what their words will mean to you after we explain them;
and lastly: how we can be so certain what we do will always work perfectly.
This page aims to help you appreciate just how much nonsense some of the others tell you and how much unnecessary product all the others would sell you only because you have no one to supervise the works and the best customer is a worried customer with deep pockets.
Many of the others sell you only expensive solutions to worries that exist only in your mind.
We explain the worries away and sell you only what you need which is concrete that is waterproof.
You could spend twenty or thirty times what we ask for and still have failures if the multi levels of defences against water ingress were used without training or supervision.
The only defence you need is the one that works - and we make waterproof concrete work.
Who else can claim they work entirely with YOUR best interests in mind?
By paying for our supervision, that is exactly what you get from us - and us alone.
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Every item in the lists is linked to its explanation below.
What you could spend your money on (and even though the expense gets ridiculous many people start off considering having every option at once):
- An effective soil investigation
- A structural engineer to design a reinforced concrete structure
- Perimeter drainage around your basement slab
- Drainage membrane around your basement walls
- Blinding under your basement slab
- Waterproof membrane under your basement slab
- Waterproof membrane around your basement walls
- A vibrating poker and two spares
- Waterproof Concrete with tapes, strips or bars
- Waterproof Concrete With Site Supervision Ltd
- Internal drainage membrane
- Internal drainage channels
- Internal sump in the floor
- Pump and outflow pipe from within your sump
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Backup pump, backup power supply, audible warning device, automatic warning to a remote location, maintenance contract, emergency call-out service, emergency key holder
What we supply:
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Chemical to make an appropriate mix of concrete fully compactible and sufficiently dense to be waterproof against a pressure of water
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Chemical to repel water and prevent capillary action
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The hire of 3 serviced, effective vibrating pokers
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Mixture to repair waterproof concrete even with a flow of water from behind (this what we use in joints in place of tapes or strips)
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Training and Supervision in ordering concrete, placing, compacting and curing concrete and repairing concrete economically and effectively
Our major competitors, what they say about themselves and what their words will mean to you after we explain them:
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Caltite from Cementaid
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Sika
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Pudlo
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Xypex
How we can be so certain what we do will always work perfectly?
Simple. If the correct concrete with the suitable admixtures to create waterproof concrete is delivered, placed, compacted and cured correctly then the unalterable chemistry of water, cement and the additives will, in about a week, make concrete waterproof against liquid and, after a few months, make concrete completely proof against water vapour.
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We will discuss the concrete mix design with your local suppliers before you order
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We will put in the chemicals on site so that they are dosed correctly for the conditions on the day
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The concrete will fully comply with BS EN 206-1: 2000
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Our training and supervision ensures no unauthorised water is added as well as good compaction without segregation
- We will advise beforehand, on the day and afterwards if need be on good design, suitable conditions and curing practices to make your waterproofing as successful as reasonably and economically possible.
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Any weaknesses, such as joints, and any leaks will be repaired under our supervision to be completely waterproof
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Steel reinforcement will be protected from corrosion almost indefinitely
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What you could spend your money on (and even though as the list goes on the expense gets ridiculous many people start off considering having every option at once):
- An effective soil investigation
A good soil investigation will include at least 2 boreholes, better to have 3; a desk study and laboratory investigation into each major soil type found.
They often cost about £3,000.
They often save £30,000.
More detail
here:
- A structural engineer to design a reinforced concrete structure
A structural engineer will include as a part of his design reinforcing steel that will restrict any early age cracking to 0.2mm. This is because relatively new concrete, when it cracks, exposes unreacted cement grains to unreacted water still in the concrete and as cement expands as it gels with water so such cracks will self-heal. (So don't listen to the drivel from Xypex about their magic, they describe what concrete does anyway).
More detail
here:
- Perimeter drainage around your basement slab
Drainage is a system carrying water. Water will flow downhill. If any water surrounding your basement will always flow immediately downhill and away, then it is a very effective defence. But all too often drainage can be overwhelmed during a deluge and then your drainage delivers water to your drainage perimeter.
Wrap perimeter drainage in filter membrane so it does not silt up.
Be absolutely certain that water will always flow away before choosing this option.
- Drainage membrane around your basement walls
This wall drainage allows water to flow speedily down your walls to your perimeter drainage.
Shingle wrapped in filter membrane is the old fashioned alternative but usually so much is needed it is too expensive.
Beware of brands like Delta whose fancy 3 layer product costs 10 times a basic bobbly membrane covered in filter membrane from your local builders merchant.
Very difficult to protect when backfilling. Obviously if silt gets in a tear it will eventually silt up your whole drainage system.
- Blinding under your basement slab
Many try to skimp on blinding under basement slabs, suggesting type 1, crushed concrete or very thin blinding.
BS 8007 (design of water retaining structures) is quite clear.
Blinding concrete is required to be not less than 75mm and not weaker than C20 or C25 in aggressive soil conditions.
A basement need not comply with BS 8007 but solid blinding makes the work of fixing and supporting reinforcing steel much easier.
And readymix concrete blinding can be down in an hour instead of taking days with other materials, so it is invariably cheaper in the end.
- Waterproof membrane under your basement slab
Usually available in rolls 20m x 1m so you need to overlap and stick together many rolls. You must also protect these products from punctures.
First this means floating your concrete blinding dead smooth and sweeping it perfectly clean repeatedly because this work is outside down a hole - a magnet for grit.
Second all the reinforcing steel needs placing and tying on top of this membrane.
You will be cleaning, sweeping and repairing for even more time than the membrane took to put down. I know some who just gave up.
- Waterproof membrane around your basement walls
This is usually the same membrane as under the slab. Whereas your initial excavation was in full sunshine, some of your walls do not see the sun and by now your excavation is damp. Sticky back membrane does not stick in humid conditions. The walls do not even need to be damp. If the air is heavy these products just do not stick.
But the real difficulty is sticking the wall membrane on to the under slab membrane where water has pooled and the edges have been trampled.
There are other membranes such as clay filled. These soak up water and expand. They typically soak up water, expand and get too heavy before the wall is backfilled by which time they are out of shape and useless.
All wall membranes tear during backfilling.
Believe me. If your concrete is not waterproofed it will suffer capillary action. With little more than a pin prick failure anywhere in your waterproof membrane in contact with water, your entire concrete structure will be kept saturated forever drying off as vapour inside.
More detail
here:
- A vibrating poker and two spares
A vibrating poker, to work well throughout a pour, must:
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be powered continually without breakdown or failure
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vibrate at 12,000 revolutions a minute loaded
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continue to do so without its core breaking or the bearing seizing up
None of these traits seem to exist whenever a groundworker's poker comes out the van and especially not if the poker is hired. Hired pokers are usually too slow.
- Waterproof Concrete from Cementaid, Sika, Pudlo, Xypex or BASF with tapes, strips or bars
These suppliers and building control officers as well as architects and structural engineers will all tell you that you must have a waterproofing strip in the joint between a basement slab and a wall.
Well. It is not true.
BS 8007:1987, Code of practice for design of concrete structures for retaining aqueous liquids, states:
Particular care to be taken when forming construction joints ...
I always find that waterproof concrete, properly ordered, placed, compacted and cured received better than Particular Care
vertical joints should be formed against a stop end ...
Absolutely
the surface of the first pour should be roughened to increase bond strength and provide aggregate interlock ...
In fact, waterproof concrete, properly ordered, placed, compacted and cured is free of laitance and just
as rough as scabbled concrete just left after the poker has passed (but note that my joint treatment
scabbles part of both surfaces later).
care should be taken to ensure that the joint surface is clean ...
There should always be an air compressor and hoses on site to blow the job thoroughly clean
immediately prior to the fresh concrete being placed against it the surface may need to be dampened
in case the older concrete takes up water from the old...
concrete waterproofed with chemicals should not take up an appreciable amount of water
Particular care should be taken to ensure that the new concrete close to the joint has an adequate fines
content and is fully compacted.
This means that the concrete must be carefully placed so as not to segregate
Although waterstops should not be necessary in properly made construction joints ... they are often used.
In my experience, the fresh concrete bonds and seals very well with the hardened concrete if both pours
were carried out properly.
The reason BS 8007 does not demand tapes, strips or waterstops is because they are an item that might, but only might, overcome poor workmanship.
But the likelihood is, if the men lay concrete badly, that they will apply tapes, strips and bars just as badly and they would not protect any from damage.
Suffice to say in conclusion that an ex Pudlo rep emailed me to say that the Pudlo hydrophilic strip often failed. That super-expensive products such as multi-material strips in cages suffer the same problems as cheaper alternative. Cementaid who supply Caltite no longer supply a hydrophilic strip because they paid out too often under their warranty.
Water bars, on the other hand, can work if they are put together well and used properly. I supervised a deep water bar on a lift pit at Excel in Docklands years ago. It took days to fabricate but looked like it should have worked.
But if the concreting is done with the right care the joint will seal on its own.
More detail
here:
- Waterproof Concrete With Site Supervision Ltd
About £50 extra for each m³ of concrete.
If 250mm thick that is just £12.50 for each m² of concrete.
Very little extra labour cost.
Done properly, with our supervision throughout, waterproof concrete cannot fail to be totally waterproof because that is its chemistry.
- Internal drainage membrane
The catch-all solution.
Let water in (through the walls, over the walls, through the floor) then keep it behind a waterproof membrane. The membrane must not be punctured, hanging a picture or TV for instance, so you must have a stud wall inside to protect it. This wastes space and adds to the costs.
But I ask you. At the design stage, how much water do you design this system to deal with?
Must be used in conjunction with the next item.
- Internal drainage channels
This carries the water from the floor and the walls to the sump.
These systems might be invaluable converting a Victorian cellar but they pose structural problems in new basements.
The drainage channel, if simple, will be in the slab concrete round the edge. But this is concrete that the structural engineer has used in his calculations to resist the starter bars being pulled out so that the walls are not pushed over.
if you want a perimeter drainage channel, return to your structural engineer for a re-design.
Must be used in conjunction with the next item.
- Internal sump in the floor
This collects the water until a pump with a float switch is activated when it pumps water up and out.
Like the drainage channel, a large sump can seriously interfere with your structural engineer's calculations. Return to your structural engineer for a re-design.
Must be used in conjunction with the next item.
- Pump and outflow pipe from within your sump
A 600mm diameter sump 600mm deep takes over 160 litres to fill. When the pump switches off some water will come back down to the sump.
Frankly, I find it impossible that anyone could build a basement so badly that 160 litres will regularly leak in. But it is great for NHBC who will never have to pay out if the basement leaks - because it is supposed to. (Note. Other insurers only require Building Regulations to be met. Only NHBC insists on the internal system).
NHBC and some architects insist that a sump is used in conjunction with the next item.
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Backup pump, backup power supply, audible warning device, automatic warning to a remote location, maintenance contract, emergency call-out service, emergency key holder
All this because internal drainage should be designed at the design stage whereas, instead, quality workmanship can be specified and monitored by the project manager or client.
What we supply:
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Chemical to make an appropriate mix of concrete fully compactible and sufficiently dense to be waterproof against a pressure of water
Like every waterproof concrete additive supplier our chemical includes a super plasticiser to make concrete flow well enough to be fully compacted with much less water than the same mix without it.
Most readymix with WRA has 55% water to cement. With our super plasticiser, the same concrete would have a slump of about 130mm with only 45% water.
This means there is less excess water pushing the grains of cement apart. It also means that the cement hydrates more slowly as less can be dissolved at once. This creates a slightly different and beneficial mix of hydrated cement crystals that will tend to block the pores between cement grains.
The simple reality is that properly ordered, placed, compacted and cured waterproof concrete will be waterproof in under a week.
It is the chemistry of cement. Unalterable by anyone. But it needs the reduced water, super plasticiser, extra cement, properly ordered, placed, compacted and cured concrete generally only achievable with supervision.
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Chemical to repel water and prevent capillary action
All good concrete would suffer from capillary action. A waterproof concrete mix design is especially good and suffers more capillary pressure.
Most waterproof concrete additives, including ours, contain something that reverses capillary action. (Only Xypex seems not to, and they permit the most water as well).
A basement wall made from waterproof concrete with a chemical that prevents capillary action will, in due course, stop drying out inside. Vapour from the wall will reduce to nil soon after the basement is heated and ventilated.
More detail
here:
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The hire of 3 serviced, effective vibrating pokers
We bring along 3 good machines to every pour we supervise.
The hire cost is part of the published and agreed fee but they need to be returned clean and undamaged else there needs to be a further charge.
I have had 6 machines on a job (where the single poker failed earlier) and 4 not belonging to me broke down.
I now pay a plant fitter to regularly take mine apart and service them. It is the only way to be sure they will work. And with 3 on site compaction equipment will not be a problem.
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Mixture to repair waterproof concrete even with a flow of water from behind (this what we use in joints in place of tapes or strips)
We recommend this action even where the joint appears to be sealed anyway because if the concrete was to crack along the join then gunning it out will induce it to do so during our preventative repair work.
We dig out all joints with an air compressor and pneumatic chisel, then we blow the chase clean before filling it with a waterproof repair mortar, such as BASF Thoro Waterplug. This is waterproof, sets in under 3 minutes and creates a monolithic structure between basement slabs and walls so that there is no longer any joint.
There are other suitable very similar products available but Waterplug does not get hot, so we prefer it.
More information here: Fixing leaks and sealing joints
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Training and Supervision in ordering concrete, placing and compacting concrete and repairing concrete economically and effectively
What we supply is knowledge and experience of the entire process. If you want to gain it from us and use it independently in future then you may.
Our major competitors, what they say about themselves and what their words will mean to you after we explain them:
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Caltite from Cementaid
Their web site: cementaid.co.uk says nothing technical or revealing.
However I can tell you that Caltite is not popular on sites. It smells strongly of ammonia although the pore blocking ingredient is apparently bitumen.
Their BBA certificate 93/2888 says Caltite is a two-component system incorporating a hydrophobic and a pore-blocking ingredient. However that is contradicted at 1.1: • 'liquid that provides waterproofing ' and • 'Superplastet' a super plasticiser.
The certificate goes on to state:
The system gives concrete enhanced durability and improved protection against reinforcement corrosion by providing a
hydrophobic action that protects resulting concrete against water ingress via absorption and hydrostatic pressure.
The use of the system gives concrete the following improved properties relative to a control:
• reduced porosity • reduced permeability
• increased water resistance • increased corrosion resistance.
This does not sound particularly impressive, however:
I have often enquired from readymix suppliers what is the prescribed Caltite mix design, and in my opinion, having studied some of the best books at university on concrete chemistry, the Caltite concrete will perform much, much better than the certificate suggests.
Indeed it will perform as well as ours.
I expect that the control referred to was already very much better than usual structural concrete and the bitumen improved the test concrete slightly further.
I do not know why BBA or BRE cannot simply declare the truth in clearer, less politically protective, language since, as you can tell from the last section at the bottom of this page, the protection is far better than merely 'enhanced', it is 'absolute'.
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The client and his project manager on this Caltite project told me that Cementaid watched much of the works and issued a certificate 3 months later. They had already been back 3 times and carried out repairs under their guarantee and were returning to carry out more repairs again soon. But by this stage they were having to tear up finished flooring in a maid's basement flat that was now occupied accommodation. I was paid for a consultation. In other areas of the basement it was obvious that water was penetrating from the repairs to the holes for threaded bar through the formwork. So they may need to take down the finished plasterboard, the stud walling and insulation to give Cementaid access. Such a shame since their maid now lives in the space.
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Cementaid will also want to sell you their water bar. Water bar works. In my experience it is a wide piece of plastic/rubber-material cast half into a slab and half into a wall. I can tell you that it requires a great deal of skill and time to make it continuous all round and it needs to be fabricated on site very precisely and accurately to be properly secured all round.
I find that with everything else done well it is not necessary.
Cementaid are well known for returning to repair failures if they approved all the work at the time. But of course they only repair their products, not any fitting out or decoration carried out before discovery of a leak (and their repairs are limited to the cost of their materials).
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Sika
From their web site gbr.sika.com/en/
'Sika® Watertight Concrete Powder
Sika Watertight Concrete Powder is a combined water resisting and HRWR/Superplasticising concrete admixture, used to enhance the workability of and reduce the water permeability of concrete it can be used to produce Sika Watertight Concrete.'
From their Product Data Sheet Sika Watertight Concrete Powder 'Sika®Watertight Concrete Powder is a combined water resisting and
HRWR/Superplasticising admixture'
From their BBA certificate 08/4606:
"5 Water penetration and absorption
Concrete containing the product has greater resistance to water penetration and water absorption than the equivalent
plain concrete."
"6 Water vapour permeability
6.1 Concrete containing the product has a lower permeability to water vapour than the equivalent plain concrete."
"19.2 The concrete must have a minimum cement content of 350 kgm³, be batched with a maximum water/cement
ratio of 0.45 and have a minimum consistence of S3."
"21.3 Concrete containing the product concrete should be fully compacted."
Sika will also want to sell you their joint strip. Some reps also insist you pour your walls in sections. If you do, you will need even more joint strip.
As with Caltite and our own concrete it should become fully waterproof if properly placed, compacted and cured. According to the RIBA web site, you can pay a premium above the chemical cost for a guarantee.
From time to time I get calls from very unhappy customers of competitor's products, basically telling me that they had found my site but chose to trust a big name but they wanted to tell me how much they now regretted that decision. I have to say that Sika has figured in these tales of remorse as often as all the others added together. One such call (from someone who became my customer for phase 2) had ordered Sika self-compacting waterproof concrete but could barely persuade the concrete to go in the wall let alone compact. The wall was a sieve and he instructed his solicitor though I do not know the outcome.
Quite evidently the concrete producer got the Sika chemicals wrong at the batching plant (unless he took over 2 hours to find the site and the concrete had set).
The lesson to be learned would seem to be that Sika do not put their chemical in or attend site unless you pay extra. No supervision at any stage, unfortunately, usually means failure.
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Pudlo
Pudlo has a great deal to say on its web site at pudloconcrete.co.uk including at least a 10% increase in concrete strength as well as reducing the passage of water*.
Their Product Data Sheet, PUDLO CWP TDS.pdf, says their control mix wcr is 45% whereas the Pudlo concrete is wcr 38%. Both mixes are quite stiff at 50mm*.
Everything they have to say is consistent with better compaction which can be explained by the Pudlo mix having plasticiser but less water. However the 45% water mix should have become relatively waterproof so perhaps it could have been more compacted or left to cure longer or better.
They also clearly point out 'It is essential that good concreting practice is performed and maintained at
every stage of the application process.' so you would need to supervise Pudlo concrete to get all the benefits.
Another claim, no doubt entirely true: '• Proven world-wide track record with over 100 year history'. The picture is their 1954 brochure.
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* According to their BBA certificate, 01/3843, the control mix had almost a third more water than the test mix with Pudlo in. Therefore, of course the test mix performed much better. There is not really any proof that the 100 year old product is making the concrete any stronger though the processed animal fat in Pudlo no doubt prevents capillary action. They get their better results with samples made with less water.
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Xypex
From its BBA certificate 05/4216 Description '1.1 Xypex Admix C-1000 NF is a reactive crystalline admixture for incorporation in concrete to enhance the
watertightness and durability in its hardened state.'
What could be crystalline in concrete? CEMENT. Cement takes up a lot of water then it crystallises releasing some of the water since not all the water taken up is in the crystals formed. Interlocking crystals is the strength of concrete which is why more water pushing cement grains apart leads to fewer crystals interlocking and less strength as well as less waterproofing.
What does the Xypex BBA certificate say is in their product?
'1.2 The product is supplied as a powder consisting of blended Portland cement and proprietary chemicals.'
Nowhere does it explain 'proprietary chemicals' but neither does it explain that it blocks pores by anything other than crystals - cement to you and me.
Xypex cannot be magic. Nothing they claim is any different to what cement does mixed with water.
Can it be better than usual cement? If it was finer then their cement would disappear first and not be a part of the self-healing that is unalterable cement chemistry when the water cement ratio is low enough.
But strangely their instructions are for 50% water. Mine, Caltite and Sika are for 45% while Pudlo's is 40%.
On that basis Pudlo's should be best but some batching plants will not mix concrete with less than 45% claiming it will not mix well enough.
The Xypex BBA certificate, in effect, merely states that concrete with it will be more durable, stronger and more resistant to water than the same concrete without it. Even if the Xypex mix is only 0.00001% better then every statement is true. And a tiny improvement is exactly what I would expect adding one more kilogram of cement to the original 350kgs.
How we can be so certain what we do will always work perfectly?
Simple.
We prescribe the same concrete mix as Caltite and Sika because that alone will keep out water under pressure after about a week if the concrete is ordered, placed, compacted and cured properly.
We prescribe the required mix formally to your local supplier then attend site to add chemicals and see that the concrete is placed and compacted properly and we discuss curing requirements with you on site.
By doing all this then the unalterable chemistry of water and cement with the additives will make the concrete waterproof, prevent capillary action and in due course vapour permeability will be too low to detect in a habited basement.
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We will discuss the concrete mix design with your local suppliers before you order
Readymix companies are used to supplying concrete with as cheap a mix as possible. A simple RC35 could be mixed thousands of different ways. Speaking to one person about what you want does not mean someone else won't alter your order. In addition, readymix companies would like to fill their days up sending lorries as it suits them, not you. If all your lorries came at once you would not place or compact it all properly. if they were too spaced apart your pump operator would get angry that he could not clean his pump. And so it goes on. We make sure we are in frequent contact with the supplier before and throughout the pour.
We must find out from you any special requirements of the concrete such as sulphate resistance. Then we will ensure the mix will be suitable.
You do not want the cost of disposing of a full load of concrete because of some site error on your part. It is horrifically expensive. Supervision on site prevents this.
From time to time the required mix can be carefully ordered but someone in the supplier's
organisation changes it, probably to reduce their cost.
I was supervising a pour as recently as January 25th 2012 and checked the ticket when the first
load arrived only to find it was different.
If we had used even the smallest amount then sending it back would have cost over £1600 on
top of buying the wasted concrete for £750.
But I rejected the full load and despite protests from the driver, the sales desk and a
rather fearful client it was replaced.
In November last year I sent back 24m³ because it was on site before I had telephoned
to say the pump was set up.
I have rejected concrete for arriving too late as well.
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We will put in the chemicals on site so that they are dosed correctly for the conditions on the day
There are two big advantages to putting the additives into the truck on site. One, the super plasticiser will not wear off too soon because the truck was stuck in traffic and, two, the site will not add unauthorised water to wet the concrete up because they will see the chemicals do it instead.
Every load of concrete is different. Our supervision copes with these differences for you.
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The concrete and our service will fully comply with BS EN 206-1: 2000; BS 8500-2:2006; BS 8007:1987 (though, actually, we exceed this Standard); and Grade 3 or BS 8102:2009.
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Our training and supervision ensures no unauthorised water is added as well as good compaction without segregation
Waterproof concrete with too much water cannot be waterproof.
Waterproof concrete segregated so that the stones are in one place (such as the bottom of a wall) and the slurry somewhere else (sprayed all over the formwork and steel) cannot be waterproof.
Waterproof concrete full of trapped air cannot be waterproof.
All these problems need to be prevented by positive action - Training and Supervision based upon experience and expertise.
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We will advise beforehand, on the day and afterwards if need be on good design, suitable conditions and curing practices to make your waterproofing as successful as reasonably and economically possible.
Normal concreting practices by experienced labour are usually quite bad - we overcome them by experienced reasoning and supervision.
In hot weather surface shrinkage cracking can quickly occur if wet concrete dries out. Do you need to prepare to prevent such cracking? How can you prevent it? We can help.
Striking formwork and moving it on after only 14 hours or so can be very bad for surface durability and detrimental in other ways. It depends on the weather, It depends on what is required. What are the economic alternatives? We can help.
The use of kickers is a notorious waterproofing weakness. How can kickers be constructed properly? Are they really needed? Can the sub contractor be persuaded he will save time and money another way? We can help.
Traditional formwork requires many holes for threaded bar. Repairing a few is simple but repairing hundreds is boring. Complacency can set in as well as laziness. Errors will be made but they are difficult to detect. Is there another way? We can help.
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Any weaknesses, such as joints, and any leaks will be repaired under our supervision to be completely waterproof
It is usual to put tapes and strips on kickers for the wall concrete to be poured against them. But then it is normal for kickers to be poor concrete and the concrete in the bottom of a wall to be largely stones.
We will try to help you avoid kickers and we will certainly work to get all the concrete to the bottom of every wall in perfect condition. In this way, joints with reinforcing steel starter bars do not need anything in the joint if all the concrete was ordered, placed, compacted, cured and supervised properly and there will be no leaks anywhere.
But as a precaution or if at any time any leaks should appear we can show you how to repair concrete easily and cheaply even with water coming through from behind.
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Steel reinforcement will be protected from corrosion almost indefinitely
This is a quote from the electronic book "Understanding Cement" by Nick Winter.
9.4 Steel corrosion
The corrosion of steel reinforcement is probably the single most common form of
concrete deterioration. Its importance is demonstrated by the mountain of
literature on the subject and also by the many enterprises specialising in
sophisticated methods of repairing concrete damaged through steel corrosion.
The following is the briefest of summaries describing the problem.
Steel that has sufficient cover of dense, impermeable, concrete (the "cover
zone") should last almost indefinitely, as the alkaline conditions in the concrete
protect it from corrosion.
However, the importance of quality control to ensure
adequate cover cannot be overemphasised; porous and permeable concrete,
made with a high water/cement ratio and containing steel near the surface, is
particularly vulnerable to damage.
Waterproof concrete placed with good site supervision easily exceeds the need for dense, impermeable, concrete.
And from a different source:
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It can clearly be seen that protection of 100 years with C47 concrete (all waterproof concrete exceeds this with supervision), needs only 10mm of cover.
Clearly, supervised waterproof concrete with more cover with good practices will protect steel longer. To refer to Nick Winter above: 'almost indefinitely'. |
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This model and citation are reviewed from
Beckett, D, and A Alexandrou. Introduction to Eurocode 2, Design of concrete structures. London: Chapman and Hall, 1997. p18. Print.
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