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.

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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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Winter Deck Waterproofing

We are in the middle of a season where main contractors and clients are insisting on deck waterproofing. You should not be waterproofing a deck in the Winter unless you are able to give a contractor 14 days notice of dry weather with a moderate temperature of 5c and rising.

Clearly, this is not possible.

If you do not follow the manufacturer guidelines the waterproofing will fail and the cost of remediation will make the cost of a delayed programme pale into insignificance.

MacLennan also has hand applied systems that we install under our 10-year guarantee, we offer more than other waterproofing and roofing contractors.

before and after adequate surface preparation

Image 1 - This shows a before and after of adequate surface preparation, ground down and free of dust and laitance. 

lumpy concrete surface

Image 2 - This shows bad preparation. A lumpy, laitance filled concrete surface will be at risk of poor adhesion. Proper preparation is essential.

removing existing waterproofing

Image 3 - Waterproofing being removed from a surface that was ground, jet washed and vacuumed. The point being that good preparation is difficult to achieve. In cold wet conditions it is impossible.

damage to cold decks

Image 4 - This shows a failure of work carried out in Winter months. Wet, cold decks make a poor surface substrate.

water damage to decks
deck conditions maclennan have dealt with

Images 5 & 6 -  Deck conditions MacLennan have been called in to waterproof in winter months.

We always advise our clients that Deck waterproofing work with any material or system must happen in the spring and summer.

They often disregard that and try and make the weather the waterproofing contractors problem.. The following rules apply winter or summer but will be even more critical in the Winter.

All surfaces must be correctly prepared. Preparation has to be grinding or scabbling and then either jet washing or vacuuming away of the ingrained dust. Removing the dust is one of the most critical elements of preparation and may require jet washing to remove ingrained dust.

It is critical that all laitance is removed and the resulting surface is sound and dust free.

Primed & Ready

Surfaces are primed in summer to prevent outgassing and aid bond. Surfaces are primed in Winter to provide a sound dry surface and aid bond.

Most Primers do not work in cold conditions or on damp surfaces. There are primers available that are less temperature sensitive and can go on a touch dry surface but they are far more expensive and still limited by site conditions..

You cannot prime a wet surface. You cannot prime a freezing surface even with special primers. This will lead to an expensive failure.

Covering up?

Covering a deck with a tarpaulin is doomed to fail. In all likelihood when you remove the tarpaulin you will spill the water onto the deck. You must use tenting and heating so as work can be carried out under it.

Contractors are always pressurizing waterproofing sub contractors to attend site when the site is clearly not ready. This serves no purpose. You cannot apply waterproof membranes to damp substrates or in cold conditions. Waterproofing contractors who know what they are doing cannot and will not attend.

The clients team is always well aware of the required environmental conditions. 5 and rising, 3 above dew point, dry ( Blue paper test) Do not use Epoxy primer at below 10c.

On-site pressure

It is site managers who when put under pressure of a time critical programme will try and pressurise the waterproofing company to carry out the work. The ones who know their job know it is wrong but want to be seen to be getting the job done.

This attitude is what leads to the millions of pounds worth of waterproofing failures every year. The job should be done properly in the right conditions.

maclennan team working
maclennan team and van

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