I just wrote a post on my www.basementwaterproofingexpert.co.uk blog relating to discussions with a local supplier, who advised me that Manchester basement conversion firms are building in risk to systems by omitting battery back-up, this on the basis that clients would not pay for it.  It's a poor design choice and I feel for the clients that sooner or later will suffer floods as and when ingress occurs during a power cut.



Another post on my http://basementwaterproofingexpert.co.uk/ blog.

This post relates to the numerous failed cementitious slurry tanking systems that we deal with and the fact that in many cases, these are installed by non-specialist contractors backed by suppliers that provide an approved status.  Tanking is not a simple or easy task and failures do occur.



Firstly, apologies for the overly dramatic title but hopefully this will provide a useful example of the implications that a basement conversion can have on a property, where the work and guarantees which stand behind it are questionable.

In 2009 I took a call from a homeowner with a townhouse property in Manchester, they had just converted their basement / cellar to a habitable space, employing a local cellar conversion specialist to undertake the work.

There had been a few hiccups with work along the way, and while this was partly unrelated to the basement waterproofing, they advised that there were visible damp issues and as a result they had lost confidence in the waterproofing installation.

The homeowners had not yet paid in full and we were asked to inspect and provide advice in respect of what had been installed and works required to resolve the outstanding issues.

When I inspected it was fairly typical (at least at that point in time) in that cavity drainage waterproofing had been installed but there were no inspection/maintenance ports for the drainage channel system, and no evident battery back-up system for the sump pump – this meaning issue in the event of power cut – with omission probably motivated by cost. It was definitely a less than perfect spec.

In addition there were minimal areas of low level bubbling paint finishes, staining and efflorescent salts.  The general patterns indicated moisture penetration and certainly warranted further investigation.

I subsequently provided a written analysis and list of considerations which needed to be addressed. The main aspect that I stressed is that they should resolve the issues, pay the outstanding money and… get their guarantees.

I heard nothing further from the client and assumed that all was well.

Fast forward to 2015, and I’m asked to inspect a basement conversion with possible issues by a Manchester Building Surveying Practice and so off I go.  I meet the homeowners, walk downstairs and there I am, back in the basement in question!

I ask the homeowner if they bought it from my previous clients, which they did, and then I start looking around.  I can see that some of the issues (plumbing) have been resolved, but still no inspection ports or battery back-up, and while I could see evident redecoration I could still see the staining, there was now deterioration in timber floor finishes at the wall floor junction to the perimeter, high % moisture content readings from softwood timber skirting boards across a fairly wide area, also efflorescent salts causing paint to bubble and debond from the skim plaster it is applied to.  If anything conditions had worsened.

Efflorescent salt deposits form when water moving through the ground and/or building materials, dissolves salts contained within those materials.  These are held in solution, however when that moisture evaporates, i.e. changes from a liquid to a gas, the salts return to a solid state and form a crystalline deposit.

I don’t know what happened between the homeowner and the contractor but clearly the issues were not satisfactorily resolved.

I sent a copy of my original report to the Chartered Building Surveyor and discussed the considerations.  His first thought was obviously that of his own client and that if the property were purchased, what would it cost to correct, with the objective of ensuring no future issues, and addressing in a manner whereby we could provide guarantee?

With cavity drainage systems the key is in ensuring that the drainage element included within the floor construction functions as intended to collect and channel water to the means of removal, in this case a sump pump system.  We can only guarantee that which we treat and so as a minimum the work would have involved opening up, stripping out to expose the structural slab and most probably improving the detailing before replacing the waterproofing system (membrane/pump/channels) so that we protect the floor construction and low level wall areas.

This was not a small space and included a bathroom.  I estimated the costs at £25,000.00.

I can only assume that the prospective purchaser asked for a reduction or walked away, probably the latter.

This is the thing.. if any member of the public calls me asking about a basement conversion with issues and/or no/questionable guarantee cover, my advice would be to consider the implications very carefully, in that personally I would not seek to buy what are potentially expensive problems.

It makes more sense to purchase a property with a basement/cellar which has not yet been converted, than one which has been converted but has such issues.

This is because there may be a substantial cost in stripping out (in this case losing expensive timber floor finishes etc.), before you can even start to correct the waterproofing.

Note: I’m not publishing photos of this basement as that would obviously not be fair to the current owners – hence the redacted feature image!

You might think that such situations are a rarity, but I’ve just advised on a converted basement apartment in Didsbury, Manchester with issues where they got the installer back to remedy under guarantee then had me get me back out again because the repair was poor.

At the time of writing I’m working on a failed conversion in Altrincham where we are stripping out and renewing the cavity drainage waterproofing system to the floor construction, where they installed only one length of channel, ran that into a gravity drain and the system failed. The specialist installer can no longer be contacted so the homeowner is having to spend £9k with us to have most of the work undertaken again.

The full article can be found on:


We've just signed off on remedial works addressing failed external tanking in a series of houses where the homeowners were initially (and understandably), very resistant to the concept of cavity drainage waterproofing.

For the uninitiated, cavity drainage involves the use of internal drainage channels linked to a suitable point of discharge (sump pump system or 100% reliable gravity drain), in association with cavity drainage membrane vapour barriers (yes the egg-carton membrane), typically installed to all walls and floors.  Water penetrates, flows down-hill through the channels, out, and is totally isolated from the interior.

It is a strange concept to many, because surely the ideal is simply to block water out, no?

Well, this is often easier said than done in a remedial situation.  It is often trialled, and often fails, only for cavity drainage to successfully remedy.

We have some poignant examples of this, from situations in which external tanking has failed, they've excavated externally, attempted repair, filled the hole back in again, and yes it leaks once more, only for cavity drainage to remedy.

We dealt with another, which was a newbuild house, where external bitumen sheet membrane was applied to protect the basement, only for this to leak during construction, so internal cementitious tanking was specified as a remedial, this was installed and they finished the basement, which then flooded, had to be stripped out, sucessfully treated with cavity drainage (by Trace), then being fit out again i.e. purchase of three waterproofing systems, two fit-outs and one strip-out... ouch.  See pic below.

Internal polymer modified cementitious tanking slurry.  This installation was inspected by the supplier during installation, but it still leaked.

Internal polymer modified cementitious tanking slurry. This installation was inspected by the supplier during installation, but it still leaked.

Look at the approach taken by each and every one of the structural warrantee providers (NHBC etc.), who employ cavity drainage time after time to successfully remedy failings in other forms of waterproofing systems.  These organisations have to resolve such issues, because if they don't, the liability remains theirs, and so it is in their best interest to fix problems right first time.

I think it is only a matter of time before the wider industry and public come to understand that cavity drainage must be employed in new construction (I'm referring to residential space) to design out such failures in the first instance.

Anyway, in every case that an independent individual questions the approach, if you provide them with enough information, they ultimately understand why suitably designed and installed cavity drainage is the right approach, providing lowest risk.

They always come around in the end.

Recently, I've had a couple of informal conversations with contractors and specifiers in relation to waterproofing products, where we discussed the role of third party product accreditation such as BBA, and in one case I was asked for an opinion on a particular product, more specifically an adhesive bitumen sheet tanking membrane produced by a particular manufacturer, (which I expect they had used on a previous scheme).

My answer (in summary): 'same as any other adhesive bitumen sheet membrane'.  Yes, a bit blasé, but I explained why I feel this way and thought that it might make for an interesting blog post.

My point was that while 'product' is important, it is just one part of the equation, with design and installation if anything being more critical, in the following order:

Oops, poor design (but awesome efflorescence).

Oops, poor design (but awesome efflorescence).

Design > installation > product.

Why? Well, if your design is incorrect then perfect installation and perfect product may not result in a dry basement.

Case in point, we've just started remedial work on a waterproof concrete basement (using an admixture in the concrete), good product and I expect that the concrete pours would have been checked and/or supervised as quality control; however, to provide a means of escape, there is a window opening through the (waterproof) concrete structure, with reveals part lined in (not waterproof) masonry, with the glazing unit fitted into the masonry recess.

The design of the external stairwell leading down to the window is such that water is able to pressure upon the masonry elements and find its way into the basement. 

Probably a simple design oversight, but enough to cause penetration and problems for the homeowner.  Nothing to do with product or the installation of it.

A classic example is the use of external adhesive bitumen sheet (or other) membrane tanking systems, which rely on effective land drain systems to prevent pressure from coming to bear, because while a BBA/other certification might imply that they are capable of totally excluding water, the reality on site is that they will not realistically be 100% free of defects, and as a result rely on the correct design of external land drain systems, to prevent pressure from coming to bear, thus negating any potential defects present.

Following Phil Hewitt's work on the Outwing Vs. Weatherald case it is more common knowledge, but you still see land drains shown too high, with failure often occurring as a result. 

Thankfully the British Standard now advises that a waterproofing specialist should be involved on the design team at an early stage.  We've been promoting such an approach at Trace for many years, because we know that good design is the first stage in achieving a sucessful outcome.  Product is important, but it is only one part of the equation.

My money would be that in the next iteration of the British Standard (8102), installation by specialists is also recommended, but that's another blog post!


Example flooded cellar due to tanking failure

What can happen when you don't get it right - tanking failure.

When dealing with waterproofing and basement design, there are typically options in respect of the methods or 'types' of system that could be selected, with the objective of creating a dry basement which stays dry in the long term.

Different systems provide different levels of protection/risk and so what we are always interested in, is the lowest risk system.  This is because we provide guarantees on the systems that we install, and so would not survive in business for very long if we employed risky systems which required us to go back, and back and back, and believe me this happens to others, which perhaps explain why there are so many basement conversion/basement design companies which start up and then seemingly dissappear year after year (another blog post in itself)! 

So, we have to justify and explain our basement design choices to the clients and professionals involved in a given scheme, which we do time and time again, however it's fantastic when a client just gets it, as experienced on an inspection yesterday.  

This chap had little in the way of construction knowledge, but securely grasped the principles explained to him in respect of why we do what we do.  He will get a dry basement. 

Although this should always be the case where a detailed explanation is given, we in some cases have to deal with preconceived notions of what 'waterproofing' is right for a given basement scheme, and it can be that the more an individual knows about construction, the more they believe they know about basement waterproofing, and the less willing they are to accept alternative ideas, even when this means a much more detailed and rationalised basement design process, versus simply choosing a product and shoehorning it into a given site and structure. 

The assumption that basement waterproofing design is a simple matter results in what must be millions of pounds of headache and remedial work each year, which the new BS8102 design guide (the UK waterproofing bible) deals with by repeatedly advising that waterproofing specialists (like Trace) should be involved in a project at the earliest stages.  

Looking back to my younger years, whenever I believed I knew it all, it wasn't typically long until I was shown that I did not.  The lesson is, that an open mind is a vehicle for learning, and that where basement waterproofing is concerned, you do not want to learn this the hard way. 

...and furthermore, listen to the advice provided by those that will have to honour the guarantee, rather than those who simply profit whether it works or not (another blog post to write!).  Also see: http://tracebasementsystems.co.uk/guarantees-not-worth-the-paper-they-are-printed-on 

Thanks for reading.

In the last month 21 people have visited our website, inputting search terms suggesting that they have problems in their basement, and we are but one company in an industry of many.  Some examples being:

Why is this?  The answer in our own opinion, is that there are many who are designing and installing waterproofing systems without the necessary understanding and experience to make systems work in any given site and structure, and we often find ourselves picking up the pieces where failures do occur.

We have hundreds and hundreds of trouble free installations dating back to the 80's, but then we are waterproofing design and installation specialists...

The British Standard 8102 (2009) Code of practice for protection of below ground structures against water from the ground, now includes a section on 'DesignTeam', which advises Architects or those managing projects, to involve a waterproofing design specialist at the earliest stages.

Good advice, which is designed to prevent problems.

For the consumer considering basement conversions, be careful who you employ and even if this is not Trace, you can certainly make use of the guidance on our website which is designed as a resource for those that seek quality installations, good service and guarantee protection.

We are happy to discuss any such topics with you and welcome your enquiries if you do have issues, or wish to avoid them.

Before and after shot of a failed tanking system successfully remedied by Trace Basement Systems

Nice photo (albeit in poor light), showing the use of a clip-rail system to install underfloor heating pipes over a cavity drainage damp proof membrane prior to screed application, on this remedial project addressing a problem of external tanking failure.  The clip-rail detail is important since it negates any requirement to fix through and therefore puncture the DPM.

membrane with UFH 1

membrane with UFH 1

This photo also illustrates the use of treated timber battens fixed and squared up ready to accept dry linings.  While many form independent studs which is quicker (cheaper), this typically loses excessive space while battens are extremely sturdy and maximise the size of the finished room.

Starting a job today which involves catching high level water penetration in a concrete car-park, and diverting it to a safe location using drainage membranes.  A previous repair was attemtped using resin injection, however this did not stop the penetration, with a typical example shown below:

Water penetration conitnues to occur following resin injection.

Example of water penetration following resin injection.

Where carefully designed and installed, drainage membranes can in the right circumstances be used to provide a safe and simple means of remedying such issues, right first time.

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