No waterbar - big ooops or not needed

[Adsibob]

We installed a concrete slab as a better structural base for our 1930s house than the suspended timber subfloor that was there before.

The build up shows hardcore on the bottom, then the slab, in both cases extended right across the subfloor of the house wall to wall. The bricks enclosing this area are below the DPC (which is a 1930s DPC in any case). The cross section drawn up by my architect shows that in between the bricks (which are either corbels or the course above the corbels) and the new slab, there is to be Koster Quellbend Waterbar.

 

The slab has been poured, a couple of weeks ago now, and I cannot recall seeing that this was installed before the pour.

 

Trying not to panic, but it is somewhat worrying. I will ask my builder if he installed it and hope he gives me an honest answer. The builder is experienced and has poured many slabs before, so if he didn't install it I'm hoping that he has good reason for thinking it was not necessary. Could that be? My understanding is that it is to make a joint between two concrete solids waterproof, even in the event of the concrete cracking. But in this case, it is a joint between concrete and old 1930s brick wall. Is it still required. It is not a basement, although we are slightly below the external ground level at this point, and I do remember that when they dug up the place to make space for the hardcore, there was some water coming up underneath.

 

If it is required, a quick google found this as an alternative of what to do:

 

"If your concrete has been set without waterstops in site, the focus should turn to waterproofing the exterior of the slab. Techniques such as torch on membrane waterproofing and epoxy coating will ensure that at the very least each of your individual concrete slabs won’t soon feel the effects of intrusive water."

 

I then googled "torch on membrane waterproofing" and it seems to be some sort of bitumen that is applied.

 

The architect has also specified that the whole slab and the walls on the side up to the DPC be coated with a waterproof repair mortar, known as RIW Cementfill HB  (details here https://www.riw.co.uk/products/cement-based-systems/cementfill-hb). 

 

So I'm now wondering what to do. Will it be sufficient to put in the RIW Cementfill HB, or should I also be doing bitumen?

 

[Oz07]

Is the slab poured on polythene? Do you have a section of drawing I don't understand why you'd need waterproofing. My slab is below dpc level of brickwork but wrapped up 

[Adsibob]

2 hours ago, Oz07 said:

Is the slab poured on polythene?

No, it was just poured onto hardcore that had a steel mesh over it so that the mesh would be embedded in the slab. Here is a drawing, although:

• it doesn't show that over the slab we are putting sand blinding, then DPM (Gauge 500)
• it does show the next layers in the build up which are PIR insulation, UFH pipes and screed, then finished floor which is microcement.

 

[Russell griffiths]

So where is the damp proof membrane in that picture. 

There are a lot of details missing from that drawing, can you pan out on it, I take it that is a screed with ufh installed. 

Edited July 15, 2021 by Russell griffiths

[Adsibob]

5 minutes ago, Russell griffiths said:

So where is the damp proof membrane in that picture. 

There are a lot of details missing from that drawing, can you pan out on it, I take it that is a screed with ufh installed. 

Yes, the picture isn't great. As mentioned above, the picture doesn't show that over the slab we are putting a layer of sand blinding, then the DPM (Gauge 500). The DPM is indicated by the black and white hatched line which goes horiztonally and then up the walls until it joins the DPC. On the walls, under the DPM, we are going to apply the waterproof repair mortar, just because the brickwork there is almost 100 years old.

On top of the DPM goes PIR insulation, then the UFH pipes then screed.

[ToughButterCup]

7 hours ago, Adsibob said:

...

there is to be Koster Quellbend Waterbar.

The slab has been poured, a couple of weeks ago now, and I cannot recall seeing that this was installed before the pour.

...

 

Does '...this...' above  refer to Koster Quellbend Waterbar ?

[Russell griffiths]

In that case I cannot see what the water bar is for. 

[Adsibob]

2 minutes ago, ToughButterCup said:

 

Does '...this...' above  refer to Koster Quellbend Waterbar ?

Yes.

[ToughButterCup]

7 hours ago, Adsibob said:

...

Trying not to panic, but it is somewhat worrying. I will ask my builder if he installed it and hope he gives me an honest answer.

...

 

No need to panic at all. None.

"Please Mr Builder, could you show me the invoice for the  Koster Quellbend Waterbar, please? "

 

" Ermmmm, it's in the post...."

 

"Oh, no invoice? Hmmm, well since it was in the spec, and there's no invoice, and no other evidence,  how are you going to remediate the problem?"

 

Do not pay without evidence. Yes, it looks like you don't trust the builder. My response (now) to that kind of challenge is - how do you expect trust to be built without evidence?

It really isn't your problem - yet. I used to trust builders: laughable I know. But just scan some of the stories I tell here on BH .. it isn't pretty.

 

Arm yourself first, pay later.  

Edited July 15, 2021 by ToughButterCup

[Mr Punter]

Absolutely no idea why there is a water bar specified.  A complete waste of money and resources.

[Adsibob]

3 minutes ago, Mr Punter said:

Absolutely no idea why there is a water bar specified.  A complete waste of money and resources.

Spoke to architect who said the engineer had specified it. This is the same engineer that told me to adopt chemical injection treatment for some damp (which I obviously didn't do), so it was somewhat reassuring to hear that it was the engineer's suggestion not the architect's.

 

The slab has actually been poured in three stages, one stage for the lower ground floor and two stages for each of two sections of the upper ground floor, as opposed to one monolithic pour.

 

Would that change the requirement for a waterbar? i.e. should it have been installed along the joints where the portions of slab meet? Engineer didn't specify waterbar there, just along the perimeter with the wall.

[ToughButterCup]

5 minutes ago, Adsibob said:

...

Would that change the requirement for a waterbar? i.e. should it have been installed along the joints where the portions of slab meet?

 

All that matters is what the SE specifies. That company has the Professional Indemnity Insurance. We are  - at best - interested , reasonably well informed amateurs. You might decide to seek the opinion of other SEs....

In our case we did and in the process saved ourselves a significant amount of money. Which is now a kitchen.

[Mr Punter]

I only ever see water bar in a basement.  I often see SEs wasting client's money on pointless items or impractical details that end up being adjusted or omitted on site.

[ToughButterCup]

2 minutes ago, Mr Punter said:

....  I often see SEs wasting client's money on pointless items or impractical details that end up being adjusted or omitted on site.

 

And do you see any of the results of SE's advice being ignored? 

Once anyone steps outside the design offered by a professional, then they become the designer, and any money you've paid to the SE is thrown down the drain. Yes, builders often ignore SE's advice and get away with it. But I have yet to see anyone who admits to a calamity being caused by their own disregard of an SEs advice. I am not an SE.

 

Get a couple of SEs  advice ... 

[Mr Punter]

5 minutes ago, ToughButterCup said:

And do you see any of the results of SE's advice being ignored? 

Once anyone steps outside the design offered by a professional, then they become the designer, and any money you've paid to the SE is thrown down the drain. Yes, builders often ignore SE's advice and get away with it. But I have yet to see anyone who admits to a calamity being caused by their own disregard of an SEs advice. I am not an SE.

 

Get a couple of SEs  advice ... 

 

Plenty of big contractors have their own SEs and will get them to value engineer the design to remove the unnecessary bits.  If we have got to the on site stage and something comes up we would approach the engineer with our suggested design and ask if would be acceptable.

 

Normally I try to do this at the design stage, before I have paid their invoice!

 

I recently got some ground floor slab mesh changed from 2 layers of A393 to a single layer of A142.  The ground is hard chalk.  The site is really restricted and I didn't fancy hefting heavy mesh about that was not required.  They also removed at our request a lot of steelwork from an earlier design that would have made demolition / temporary works very awkward.

 

I do agree it is not sensible to just ignore what has been designed.

[Adsibob]

Builder has now said he did install the waterbar. Odd, because I can't see anything at the edges with the wall. If it had been installed, wouldn't it be showing at the top as per the diagram above? 

I fear that if I adopt @ToughButterCup's suggestion of kindly asking the builder for "the invoice for the  Koster Quellbend Waterbar" he will get defensive and so only want to go down that route if this waterbar is really necessary.

 

I note that bitumin DPM paint/sealant, such as this is cheap. For a belt and braces approach, would there be any downside to painting an additional membrane onto the slab and joins using something like this paint?

[ToughButterCup]

24 minutes ago, Adsibob said:

... asking the builder for "the invoice for the  Koster Quellbend Waterbar" he will get defensive... 

 

Oh how I know that feeling.

It's horrible, jangly, itching powder down yer shorts, fart hard infront of the Bishop  type of feeling. Not facing - directly - the kind of challenge that you have, could well lead to the kind of post that I have had to write: broadly they could all be titled  ' Living with my mistakes '. Another one in that series is brewing later today.

 

There's no easy way of putting this: ask him with a smile - for the invoice. You could say that you're just being cautious. Is there an empty cardboard box for the waterstop material : in the skip maybe?

And if he gets defensive, then you'll know your builder better won't you? And you'll pay less. (no evidence)

 

But if he shows you a valid invoice, then trust is beginning to be built.

Just a thought: a time lapse camera  - and permission to take images from the builder - saved me a few thousand quid. In the end I used two cameras......It might also reassure you. 

Edited July 15, 2021 by ToughButterCup

[Adsibob]

So the update is that I have had a more careful look and I can definitely see that the Waterbar has been installed on two of the four walls of the house. As for the other two, one is the rear wall which is brand new (extension) so maybe not required there. Other wall is front of house, which was the wall where I remembered NOt seeing it and it is where I think I would be most concerned about damp. I cannot see it there, so either he forgot or he covered it over with the pour, rather than leaving an edge exposed. A bit more relaxed about the situation as it seems that at most wet need to tank that front wall join, or he can reassure me that he really did install it there.

[ToughButterCup]

?

[George]

Only need a water bar if the concrete is water retaining/potentially water retaining (for example, base slab of a basement floor).

[Adsibob]

8 minutes ago, George said:

Only need a water bar if the concrete is water retaining/potentially water retaining (for example, base slab of a basement floor).

The concrete is water retaining to an extent in that whilst it is just a foundation for a ground floor extension, the external side of that foundation is exposed to london clay soil which really gets wet. In the recent heavy rain we've had, water has pooled in the gaps between the clay and the concrete, the concrete has got wet and as a result the water bar has swollen as it has absorbed / reacted with the water. We are in the process of digging and installing french drains along the perimeter of the extension which will somewhat deal with this, but I wonder if this is the reason the structural engineer specified it?