maclennan engineer sealing around external waterproofing service ducts

When you just have to punch a hole in your basement.


David Keffen CSSW

As an active member of the Maclennan design team, I see numerous waterproofing challenges in the course of a week. We have an advantage over Engineers and Architects in that we specialise in waterproofing, and therefore the challenges faced by the Basmenteer are not unfamiliar to us.

This is no negative reflection on the engineer or Architect as they are advised by the British Standard BS8102:2009 to call us in.

A waterproofing specialist should be included as part of the design team so that an integrated waterproofing solution is created. The waterproofing specialist should:

A: Be suitably experienced.
B: Be capable of devising solutions that accommodate the various project constraints and needs.
C: Provide the design team with information and guidance that assists with and influences the design, installation and future maintenance of the waterproofed structure.

- British Standard BS8102:2009

Here's a typical scenario highlighting a fairly common problem, I wonder if you can identify with it?

The main contractor is starting to see light at the end of the tunnel. The end of the project in site (only a month over Programme dates but that has all been accounted for now) ... The basement M & E is nearing completion (finally!). Then they get a phone call from the clients representative "The clients have suddenly decided that they require an extra sauna, plunge pool and shower facility on Basement level 3...Oh and 'A Multi Media and Technology Command Centre'.." that necessitates a further bundle of fibre optic cables. (Are you imagining Bond Villain now? Interestingly they aren't as rare as one might imagine... Multi Media and Technology Command Centres...I mean, not Bond Villains).

Is that doable? Well, yes apparently 'it is' according to the engineer calling in from a Beach Barbados having thought her work was over, but only with two more support columns and another 5 pipe penetrations through the retaining wall on the top basement level.

Hmm that's a nuisance; even the 3 additional 150mm service pipe penetration sleeves installed in case of emergencies are not going to be enough.

Familiar tale? What is the best approach to these problems?

Well, best of all (as I have already alluded to) would be to ask a waterproofing specialist for some design input after all they have already made sure the basement is completely dry so far. That's where we come in.

Question: Where are the services in relation to the basement?

Top Answer: That they can all enter the basement via a dry riser from a dry space in the Ground Floor building, but as we know that is not always practical. So what is best practice from there on?

Next Best: Well certainly keep them as near ground level as possible. The lower they sit, the higher the chance of hydrostatic pressure causing a leak, especially if they are hot services. If they are just below ground level, then it might be practical to provide a dry space such as a manhole or service trench that can also be waterproofed, lessening the risk. Unfortunately it's too late for that/ there is not enough room. What next?

Not as Good, but Workable: No chance of any dry space externally, but they will be brought in near ground level. Quite a common problem alas but there is always something worse lurking:

Dire: No dry space externally, base of the wall. High Water table. Maximum risk.

OK, so let's just cut out the flimflam and get down to brass tacks. How do we approach this worst-case scenario?

I’m pushing the boundaries slightly here for the purpose of this article as it is highly unlikely that this would be necessary, but we have seen the odd one here and there.

It is tempting to tell the client's design team in no uncertain terms to 'go back to the drawing board' (remember them?), but as we know, that may not be the option and we are here to help our clients in the best way we can.

At the base of a wall (yes we have seen this, and been told categorically that this 'has to be like this') the only truly safe approach is to use mechanical gasket systems such as that produced by a rising number of engineering companies. We might use other flexible waterproofing products when the risk is low, but these rely on service not being able to move as the products remain flexible, and as we know, pipes and cables get pulled and pushed in plant rooms so even with extreme clipping; even when the flexible material is capped with a Natural cement repair mortar plug, there is always a chance the seal will be broken.

First of all the core. Certainly, an oversized and safe access trench (either battered back or properly shuttered temporarily) would need to be dug in order to pump out the groundwater and provide a safe, dry space externally while the core drilling takes place. Next there are a number of options with sleeves that can be retro-fitted (too many to mention here). Some are designed with crystalline coatings that merge with the concrete in order to alleviate the need for Hydrophilic strips, others rely entirely on mechanical fixing plates attached to the face of the concrete as a flange. Sleeves should protrude to allow attachment to the cavity membrane system (you would be fitting this if we are involved as it is the most reliable form of waterproofing).

Next the plug. Mechanical gasket systems are generally well-engineered products that are robust and reliable. They should be the 'go to' product in risky (and perhaps not so risky) situations. The mechanical plug has a rubber EPDM press seal core that is pre-drilled to the size of each of the services running through the duct, and then a metal plate is compressed using bolts and a torque wrench to squeeze the joints tight. It is important, as with all service ducts that services are not bundled together. This means that our fibre optic cables would need to be separated and the gasket would be drilled for each cable individually.

It is imperative that these are sized exactly and then fitted by trained Technicians who understand how to fit them with correctly, or inevitably trouble will follow.

Maclennan are expert waterproofing specialists, and are not tied to any one manufacturer’s system. We are approved installers of all the leading manufacturer’s products and will always specify the best product for each individual situation. Our main objective is a ‘Leak Free’ basement.

So the morals of our story are that if you have a basement to waterproof involve a design specialist at an early stage so we can do full solution for you and if you must drill holes in your lovely water-tight structure after we have protected for you, and you need your penetrations sealing, give us a call for a full design and installation service that is second to none.

If you found this blog helpful or would like to hear more technical advice, try booking a CPD with MacLennan! We offer free, lunch provided 1 hour CPD's at your premise.

CPD Booking Form

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Waterproofing, Better by Design.

ian scroggins

Ian Scoggins CSSW

I have worked in the construction industry for 28 years and have been specialist waterproofing surveyor for 12 years, my time as a waterproofing specialist has given me a rounded experience of the industry.

During that time in the industry, I have seen projects that have gone very well and some not so great.

Based on my personal experiences, I have come to realise that its early engagement and collaboration with the overall design team that delivers the best results. By everyone investing time in early engagement, I find that designs can often be simplified as sitting around a table and everyone giving their input can often take out expensive complexity and give a much better overall solution, that ultimately benefits the end client.

This only works when the correct sub-contractors are engaged on project early, so they are associated with the project from day one, one thing that sets us apart from manufacturers offering technical support is that we are involved in projects on-site every day and know the practical solutions to problems that aren’t always evident when looking at a drawing.

When it comes to high-risk elements like the basements and waterproofing, going out for multiple tenders and the lowest bidder often leaves you with skills and scope gaps as there is a clear lack of ownership. It can then become about delivering a solution to a budget, rather than a simple but effective solution that works with all the other key partners on the project in mind that’s actually deliverable on-site.

This doesn’t mean the client shouldn’t benchmark the competition and capabilities, as I live in the real world and want to offer real value for money to my clients but I want to do this without them un-intentionally building in unnecessary risk by accident by being insightful and helpful early on. It’s what falls between the cracks where the real risks sit (no pun intended) that really sets out your specialist subcontractor as part of a collaborative team that makes all the difference.

"My role is as much about sleeping well at night, as it is about waterproofing."

As myself, my MD, our insurance company, the main contractor and my end client all want to never ever worry about what the waterproofing is doing as it’s a hidden system in their beautiful property that just does what its supposed to. Its why our company takes full design and solution responsibility and hold genuine guarantees as we offer our clients leak free basements from a waterproofing perspective rather than material warranties.

If you found this blog helpful or would like to hear more technical advice, try booking a CPD with MacLennan! We offer free, lunch provided 1 hour CPD's at your premise.

CPD Booking Form

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Weymouth training tunnel photo

Dorset & Wiltshire Fire Training Tunnel – Waterproofing Project

This was a truly unique project with its own important design considerations to be undertaken.

The training tunnel is a deep pit and tunnel system used for training Wiltshire & Dorsets fire & rescue service in emergency scenarios.

The issue is that it was full of water and could not be used!

Previous attempts to stem the flow had failed so MacLennan were tasked with stopping the water ingress and getting the facility back in use.

We visited the training tunnel in Weymouth, and discussed the project intentions with them. We were able to come up with a suitable spec to fit all of their requirements.

The MacLennan technicians carrying out the work were fully trained and certified in confined space working and NVQ qualified in Waterproofing.

Weymouth training tunnel photo

MacLennan technicians carried out a day of resin injection works to initially stem the flow of water, which allowed us to prepare the surface to receive a specialist coating.

We also allowed for a cementitious coating to the entire interior walls of the structure, with over-banding to the joints. MacLennan re-detailed joins in the concrete then overcoated all the surfaces.

The client asked us to provide an environment without standing water.

MacLennan stopped the water ingress and as a backup installed pumps in a sump, ready to kick in and clear the tunnel.

The sump was cast in place with concrete in the base of the deepest point of the tunnel. The client chose to have a pump control panel with a high-level water alarm attached as part of their system, ensuring they would be notified in case of any future pump failure of extenuating circumstance.


The Advanced Control Panel chosen offers alternating duty between the duty and standby pumps

This minimizes the risk of seizure to an inactive pump and will give an output reading of the pump hours in use, flow rates and will monitor the performance of the pumps by measuring the load impedance.

wilts and dorset fire service badge

The project was completed on time and within the agreed costs, with the facility quickly returned back to use.

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