Basement waterproof concrete (Type B)

[Moonshine]

Has anyone used waterproof concrete (Type B) for waterproofing of a new basement?

 

https://www.sikawaterproofing.co.uk/products-systems/sika-watertight-concrete/

 

I am looking at this a a possible solution for a semi basement as one level of waterproofing to meet Grade 3 conditions.

 

There is a 60% uplift in material costs of waterproof concrete cost over standard, but it could save a load of material cost and labour to putting a Type A barrier on the external side of the retaining wall.

 

Any experience? 

Edited January 26, 2021 by Moonshine

[Bitpipe]

I used this exact system. BCO and warranty provider accepted it as a single method of protection.

 

We had ground water at 6m and were excavating to 3.5m (with subsequent slab build up of 150mm compact type 1, 50mm blinding, 300mm EPS insulation, 300mm concrete).

 

Came with a 15yr warranty and all works were regularly inspected by a Sika rep during the installation.

 

The crew used the Sika red waterbar held in place with the Sika red mastic for section joins (horizontal and vertical) and pipe sleeve penetrations (fouls) and the concrete had the admix. We used shuttering so the quality of the pour was visible when it was struck (this is the one issue with using ICF).

 

Sika plugs (rubber bungs that expand when a screw is tightened) filled the holes used to brace the shuttering.

 

The shuttering design needs to allow for a recess / channel in each cast section to hold the waterbar and the team were diligent at making sure that was clean and dry. They also designed a 150mm high kicker as part of the slab pour with a recess in the centre of that.

 

Also important is a land drain to the perimeter of the slab foot to a soakaway and backfill the working space with something fast draining like clean stone - in effect create a giant french drain.

 

Type A can be effective but sometimes difficult to install and backfill needs to avoid any damage. Type C (internal membrane, sump & pump) obviously assumes water is getting in.

[Mr Punter]

46 minutes ago, Bitpipe said:

I used this exact system. BCO and warranty provider accepted it as a single method of protection.

 

Which warranty provider did you use?  NHBC still state:

"Alternatively, where the builder has demonstrated that the water table is permanently below the underside of the lowest floor slab, a Type B structurally integral concrete system is acceptable without further protection from a combined system."

 

So if the water table cannot be guaranteed by an engineer they insist on type C.

[Moonshine]

45 minutes ago, Bitpipe said:

I used this exact system. BCO and warranty provider accepted it as a single method of protection.

 

Who was your warranty provider? It would be great if I could get away with single method of protection, though the habitable space in the basement is limited to about 7m of retaining wall and may install a type 3 system in here just to make sure. Did you put a geodrain or similar on the outsite of the retaining wall?

 

The ground investigation of the site found no ground water within any boreholes to depths down to 40.70m, and the lowest proposed raft is located at 42m, The groundwater levels in the area (sample point 7km from the site) are circa 26m.

 

 

46 minutes ago, Bitpipe said:

The shuttering design needs to allow for a recess / channel in each cast section to hold the waterbar and the team were diligent at making sure that was clean and dry. They also designed a 150mm high kicker as part of the slab pour with a recess in the centre of that.

 

The retaining wall isn't going be a shuttered wall but a probably a reinforced concrete block (100mm) work retaining wall (total thickness 350mm), with 150mm concrete filled cavity, hopefully with sika waterproof concrete. 

 

[Bitpipe]

3 hours ago, Mr Punter said:

 

Which warranty provider did you use?  NHBC still state:

"Alternatively, where the builder has demonstrated that the water table is permanently below the underside of the lowest floor slab, a Type B structurally integral concrete system is acceptable without further protection from a combined system."

 

So if the water table cannot be guaranteed by an engineer they insist on type C.

 

I did not use NHBC, that's for sure.

 

I went through a broker, believe the insurer was called ARK however they went into admin but the policy was sold on and is still active.

 

My ground investigation was carried out by a firm which uses chartered engineers and included bore holes, dynamic probing and gas/water monitoring. 

[Bitpipe]

3 hours ago, Moonshine said:

 

Who was your warranty provider?

 

Ark I think but they're now defunct. Plenty of others around.

 

3 hours ago, Moonshine said:

 

It would be great if I could get away with single method of protection, though the habitable space in the basement is limited to about 7m of retaining wall and may install a type 3 system in here just to make sure. Did you put a geodrain or similar on the outsite of the retaining wall?

 

Nope, just waterproof concrete. There is a landdrain at the foot of the slab and the working cavity is backfilled with clean stone so a giant french drain.

 

3 hours ago, Moonshine said:

 

The ground investigation of the site found no ground water within any boreholes to depths down to 40.70m, and the lowest proposed raft is located at 42m, The groundwater levels in the area (sample point 7km from the site) are circa 26m.

 

 

 

The retaining wall isn't going be a shuttered wall but a probably a reinforced concrete block (100mm) work retaining wall (total thickness 350mm), with 150mm concrete filled cavity, hopefully with sika waterproof concrete. 

 

 

You'll need to get Sika to sign off on that but if the entire cavity is contiguous and is within the max single pour limits then you may be ok for vertical joins. Need for waterbar arises when you join two pours. At a minimun you'll need it where the vertical wall meets the slab (or stub kicker wall) i.e. the horizontal joins.

[Mr Punter]

3 hours ago, Moonshine said:

The retaining wall isn't going be a shuttered wall but a probably a reinforced concrete block (100mm) work retaining wall (total thickness 350mm), with 150mm concrete filled cavity, hopefully with sika waterproof concrete. 

 

I think an issue may be that you cannot inspect the concrete of the join at the floor / wall / kicker junction so SIKA are unlikely to guarantee this.  In my opinion, if you are made to use type C anyway, you may as well save your money and just use normal concrete.

[Mr Punter]

By strange coincidence I just got an email from the purchaser of the house where we installed the type C system.  8 years from completion, has since been sold on and there is a problem with the basement.  I assume it is a failed pump plus lots of rain.  I have put them in touch with the contractor.  I can't say I am a fan of below ground basements and I can see why the warranty guys want 3rd party warranties to escape any liability!

[mvincentd]

I think you'll find Sika want their concrete thickness at 200mm minimum to guarantee its waterproofness (is that a word).  If your blocks only have 150 cavity i'd think thats a problem even before addressing the fact the cavity can't really be continuous...can it?

 

Personally i'd sleep easier with an external membrane on standard concrete (given it is somewhat water resistant!), versus just wp concrete.

 

[Moonshine]

On 26/01/2021 at 15:33, Mr Punter said:

I think an issue may be that you cannot inspect the concrete of the join at the floor / wall / kicker junction so SIKA are unlikely to guarantee this.  In my opinion, if you are made to use type C anyway, you may as well save your money and just use normal concrete.

 

 

12 hours ago, mvincentd said:

I think you'll find Sika want their concrete thickness at 200mm minimum to guarantee its waterproofness (is that a word).  If your blocks only have 150 cavity i'd think thats a problem even before addressing the fact the cavity can't really be continuous...can it?

 

You are right, i have spoken to SIKA and they a reinforced concrete retaining wall with a minimum thickness of 175mm designed to maximum crack width or 0.3mm.

 

They want to be able to inspect the concrete once poured which they would not be able to do if its behind a blockwork wall.

 

Two options going forward i think

 

- Cavity filled blockwork retaining wall with Type A barrier to exterior, and Type C to internal habitable spaces.

- cast in situ retaining with Type B barrier (waterproof concrete), and Type C to internal habitable spaces.

[Mr Punter]

On 26/01/2021 at 23:36, Mr Punter said:

By strange coincidence I just got an email from the purchaser of the house where we installed the type C system.  8 years from completion, has since been sold on and there is a problem with the basement.  I assume it is a failed pump plus lots of rain.  I have put them in touch with the contractor.  I can't say I am a fan of below ground basements and I can see why the warranty guys want 3rd party warranties to escape any liability!

 

Update on this it was actually a mini pump station for drainage from a bathroom that failed.  I suggested they buy a replacement pump.

[Moonshine]

43 minutes ago, Mr Punter said:

 

Update on this it was actually a mini pump station for drainage from a bathroom that failed.  I suggested they buy a replacement pump.

 

nice one and glad it was an easy fix ?

[Bitpipe]

On 26/01/2021 at 23:36, Mr Punter said:

  I can't say I am a fan of below ground basements and I can see why the warranty guys want 3rd party warranties to escape any liability!

 

5 years in and our basement has never had any issues - any system will work provided it's properly specified and installed. But any waterproofing system that is not independently, insurance backed, warrantied should be avoided as if it fails, you'll be responsible.

 

1 hour ago, Moonshine said:

 

- Cavity filled blockwork retaining wall with Type A barrier to exterior, and Type C to internal habitable spaces.

- cast in situ retaining with Type B barrier (waterproof concrete), and Type C to internal habitable spaces.

 

Given your ground water levels are so low, I'd forget type C. You will have pumps that will not be in use but will still require testing and eventual replacement plus monitoring systems for failure etc.

 

Any water ingress risk is going to be from rainfall pooling at the foot of your slab so ensure you have a robust perimeter drainage solution  - land drain to soak away at the appropriate depth - and specify backfill with clean stone.

 

Go for A as your main barrier (get a decent warrantied system) and use basic WPC as your backup.

 

 

 

[Moonshine]

10 minutes ago, Bitpipe said:

Given your ground water levels are so low, I'd forget type C. You will have pumps that will not be in use but will still require testing and eventual replacement plus monitoring systems for failure etc.

 

Any water ingress risk is going to be from rainfall pooling at the foot of your slab so ensure you have a robust perimeter drainage solution  - land drain to soak away at the appropriate depth - and specify backfill with clean stone.

 

Go for A as your main barrier (get a decent warrantied system) and use basic WPC as your backup.

 

 

I shouldn't need pumps as its a 3 sided basement and i think that i can get the drainage channel out the front open side and be drained by gravity.

 

Most of the warranty providers seem to want two waterproofing systems, even in the garage area!

 

 

[Andy H]

On 26/01/2021 at 10:35, Bitpipe said:

We used shuttering so the quality of the pour was visible when it was struck (this is the one issue with using ICF)

Could you expand on this please. I am planning to do an ICF build with the the first course starting at 0.7-0.8m underground but am not clear what you are meaning.

 

Thanks 

 

Andy

 

Just found the explanation in a later comment - you mean that as the concrete is within the ICF you cant inspect it

Edited January 29, 2021 by Andy H
found the answer in a later comment

[Gus Potter]

 

55 minutes ago, Andy H said:

 

"Just found the explanation in a later comment - you mean that as the concrete is within the ICF you cant inspect it"

 

Is this an elephant in the room for basements with a high water table? If you stop for lunch, or the concrete wagon is delayed on a hot day and you have some interruption in the pour where you have say no water bar what are the solutions? or do you just hope for the best even though you suspect that your waterproof concrete has a potential weak spot in it.. loss of aggregate interlock?

 

A point?..  you have "insurance, warranties etc" but if it goes wrong you can spend a lot of your life sorting it out, paying for professional advice etc.  One idea of self building is to have something that no one else has and be able to enjoy it to the full.