Internal cavity drain membrane

[Gus Potter]

Thorfun ..Thanks for posting, also great posts from all, so thank you.

 

There may be space on Build hub for a section that explains the geotechnical side of things. I don't know?

 

It's great to see folk delving into this stuff and trying to get a handle on it.

 

There is a lot of information on build hub about this aspect, but from time to time there seems to be the "elephant" in the room. If you are a lay person how do you interperate the geotechnical info, what the Engineers are saying and how the other "water proofing" companies are digesting this, quoting and caveating.

 

What is required in lay terms is clarity (often missing) regarding what the ground conditions are and so on, and more importantly a layman's guide to the implications of this. But the problem is that for the professional this carries a serious amount of liability, also some are not good at explaining / engaging with the self builder so sometimes it also a people thing.

 

It looks like from the posts that you still have options but can't get the clarity on the actual ground. In other words you have the icing on the cake nearly sorted but have no idea what the base of the cake will be.. and if it's a different base this introduces lots of uncertainty.. and that is not comfortable.

 

Anyway I'll have a stab at Thorfuns last post for members that may not be so familiar with the terms used.

 

"No ground water encountered" Well that was at the time of the investigation. Thorfun...  you may have to post more detail.

 

One elephant / caveat is the mention of a "perched water table" One simple way you can look at this is to take the different glacial periods. During this time various layers of materials were laid down. You could have bed rock, a gravel / chalk layer over a large area but just below your house is a layer of clay (cohesive material). What happens here is that the main aquifer / water table is well down but locally you have a more "water proof" layer just below the surface and the water this traps (leaky drains or just rainfall) will run into your house.

 

So when you read that last paragraph of Thorfun's post it's caveated such that it has less value. This will have a major impact on the design and associated cost.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Thorfun]

10 hours ago, Gus Potter said:

Thorfun ..Thanks for posting, also great posts from all, so thank you.

 

There may be space on Build hub for a section that explains the geotechnical side of things. I don't know?

 

It's great to see folk delving into this stuff and trying to get a handle on it.

 

There is a lot of information on build hub about this aspect, but from time to time there seems to be the "elephant" in the room. If you are a lay person how do you interperate the geotechnical info, what the Engineers are saying and how the other "water proofing" companies are digesting this, quoting and caveating.

 

What is required in lay terms is clarity (often missing) regarding what the ground conditions are and so on, and more importantly a layman's guide to the implications of this. But the problem is that for the professional this carries a serious amount of liability, also some are not good at explaining / engaging with the self builder so sometimes it also a people thing.

 

It looks like from the posts that you still have options but can't get the clarity on the actual ground. In other words you have the icing on the cake nearly sorted but have no idea what the base of the cake will be.. and if it's a different base this introduces lots of uncertainty.. and that is not comfortable.

 

Anyway I'll have a stab at Thorfuns last post for members that may not be so familiar with the terms used.

 

"No ground water encountered" Well that was at the time of the investigation. Thorfun...  you may have to post more detail.

 

One elephant / caveat is the mention of a "perched water table" One simple way you can look at this is to take the different glacial periods. During this time various layers of materials were laid down. You could have bed rock, a gravel / chalk layer over a large area but just below your house is a layer of clay (cohesive material). What happens here is that the main aquifer / water table is well down but locally you have a more "water proof" layer just below the surface and the water this traps (leaky drains or just rainfall) will run into your house.

 

So when you read that last paragraph of Thorfun's post it's caveated such that it has less value. This will have a major impact on the design and associated cost.

 

 

you make a very good point here in that I am a lay person and don't know how to fully interpret the GI which is why I pay professionals to do the stuff I can't and sometimes I pay professionals to do stuff I can do just because I don't have the time or couldn't do it without looking like a cowboy.

 

for the basement I am very happy to leave it in the hands of an expert. BS 8102:2009 mentions requiring a waterproofing expert to be involved (which the architects did) and I've also read that Type C is the most reliable form of waterproofing. I also think the quote I received for installing the internal membrane is very reasonable and a fair price to pay for professional work and a 10 year guarantee! as such, I really don't have a problem going down this route but I do have an open mind if the ground works company state another way and will guarantee it. I have asked the waterproofing company if they're seen the GI or just did a desktop survey. I'm sure I'll get a response next week as they've been very approachable and open so far.

 

The problem with our GI is that it was done in July when we were having the massive dry spell and great weather! so it's very possible that over the winter period we will have groundwater. so, again, I would be happy with going a little over the top with the waterproofing for piece of mind rather than spend more money on another GI in the winter, especially as we hope to break ground in a month or two.

 

thank you for the explanation about a perched water table it's not something I knew and hadn't Googled it yet!

 

I can provide more information if required on my GI. just let me know what you want to know.

[Bitpipe]

On 30/10/2020 at 20:53, Thorfun said:

 

the ground investigation went down to 2m when they hit sandstone. there was no evidence of ground water but the survey was done during the summer. we're on clay which isn't very free draining either.

 

 

the internal membrane will be warrantied for 10 years. and it is my understanding from Part C that basements should follow BS 8102 which states 2 forms of waterproofing for habitable spaces, right? so, internal membrane (Type C) and then one of either Type A or Type B.

 

 

yes, it does seem a little defeatist but our neighbours have a cellar and they didn't use Type C and then had water ingress so had to add internal waterproofing after it was built. I'd rather not have to go through that if I can get it right from the off. but, as I did say, when I speak to the ground workers I will find out what they think and then take it from there.

 

Also, we need a sump and pump to remove the water from our sunken courtyard and so the internal drains will go to that sump and pump and so there isn't an extra cost involved as we need one anyway.

 

no decision has been set in stone on this yet, even though if I make changes at a later date I will probably need to go back to the structural engineer and civil engineers to amend the plans which will incur an extra cost. I'm not set in my ways, if a better solution can be found then I will take it. I'm happy to admit if I'm wrong.....just not to the mrs.

 

Nothing wrong with internal membrane, and if you're already investing in sumps & pumps then it makes sense. Type C will work every time as it assumes the worst - leaky walls.

 

I'd just be wary of overspending on the waterproof concrete if you decide to meet the BS standard as you do pay a premium for the high quality warrantied systems (Sika etc) and they require more labour to properly apply the water bar, mastic, plugs etc but I was happy to do so as it was my only line of defence. This is probably where you can have a value driven conversation with the groundworkers.

 

The BS standard is fair but I wonder if it pre-dates the advances in concrete technology. Have to say that our building warranty did not mind that we did not meet it, but then again it was standing on the shoulders of the Sika warranty.

 

Did your neighbour have a warrantied waterproof concrete system?

 

 

[Bitpipe]

12 hours ago, Thorfun said:

for the basement I am very happy to leave it in the hands of an expert. BS 8102:2009 mentions requiring a waterproofing expert to be involved (which the architects did) and I've also read that Type C is the most reliable form of waterproofing. I also think the quote I received for installing the internal membrane is very reasonable and a fair price to pay for professional work and a 10 year guarantee! as such, I really don't have a problem going down this route but I do have an open mind if the ground works company state another way and will guarantee it. I have asked the waterproofing company if they're seen the GI or just did a desktop survey. I'm sure I'll get a response next week as they've been very approachable and open so far.

 

 

Have you interacted with the SE who designed the structural aspects of your basement or have you reached this stage yet?

 

Make sure the SE used has experience of habitable basements etc and not just foundations.

 

I'd then get their personal interpretation of the GI wrt waterproofing requirements as opposed to a potential supplier.  I always feel that when a vendor is involved, they have an agenda to sell, even if they're very decent etc..

 

Where possible suppliers should quote against a spec generated by a 3rd party - then makes it easy to get a few quotes and do a proper comparison.

 

But you've hit the nail on the head - if your GW will warranty (and needs to be insurance backed, in-case they cease trading) then you're good.

 

 

[Thorfun]

3 minutes ago, Bitpipe said:

I'd just be wary of overspending on the waterproof concrete if you decide to meet the BS standard as you do pay a premium for the high quality warrantied systems (Sika etc) and they require more labour to properly apply the water bar, mastic, plugs etc but I was happy to do so as it was my only line of defence. This is probably where you can have a value driven conversation with the groundworkers.

 

this is a very valid point and definitely something I'll be taking up with the ground workers and whichever warranty company we decide to use (assuming we do but that's a whole other topic!). both the ground workers I've spoken to so far have said not to bother with waterproof concrete as standard concrete is pretty darn waterproof already. so with the Type C waterproofing it's possible that I wouldn't need it if it's not a warranty requirement. the other option is to use Type A and Type C if Type A is a lot cheaper than waterproof concrete. ultimately it wouldn't matter if the external tanking leaked as I'd have the internal membrane to fall back on.

 

these are all decisions I will need to make a little further down the line. for now I think I'm happy with the internal membrane solution that's been designed.

 

8 minutes ago, Bitpipe said:

Did your neighbour have a warrantied waterproof concrete system?

I never asked that question. they just said that it was rubbish and they had to get someone else in to rectify it. so I'm going to hazard a guess that they didn't! I will ask the question at some point I'm sure.

[Thorfun]

2 minutes ago, Bitpipe said:

 

Have you interacted with the SE who designed the structural aspects of your basement or have you reached this stage yet?

 

Make sure the SE used has experience of habitable basements etc and not just foundations.

 

I'd then get their personal interpretation of the GI wrt waterproofing requirements as opposed to a potential supplier.  I always feel that when a vendor is involved, they have an agenda to sell, even if they're very decent etc..

 

Where possible suppliers should quote against a spec generated by a 3rd party - then makes it easy to get a few quotes and do a proper comparison.

 

But you've hit the nail on the head - if your GW will warranty (and needs to be insurance backed, in-case they cease trading) then you're good.

 

 

 

yep. SE is involved in this part of the process as are the civil engineers (trying to get the civil engineers, waterproofing experts, structural engineers and architects to coordinate is a challenge in itself but what doesn't kill you makes you stronger, right?). And they've had the GI report but as Gus pointed out just because there was no water found at that time doesn't mean there won't be at a wetter period of the year. we're not on free draining soil so there's a high chance of water pressure building up. 

 

don't worry I am very cynical and will not just blindly accept one companies solution which is why I am approaching this with an open mind and so the plans might change.

 

once I've got the SE and CE plans sorted out I can get quotes from GW and then those discussions can be had.

[Pocster]

10 hours ago, Thorfun said:

 

this is a very valid point and definitely something I'll be taking up with the ground workers and whichever warranty company we decide to use (assuming we do but that's a whole other topic!). both the ground workers I've spoken to so far have said not to bother with waterproof concrete as standard concrete is pretty darn waterproof already. so with the Type C waterproofing it's possible that I wouldn't need it if it's not a warranty requirement. the other option is to use Type A and Type C if Type A is a lot cheaper than waterproof concrete. ultimately it wouldn't matter if the external tanking leaked as I'd have the internal membrane to fall back on.

 

these are all decisions I will need to make a little further down the line. for now I think I'm happy with the internal membrane solution that's been designed.

 

I never asked that question. they just said that it was rubbish and they had to get someone else in to rectify it. so I'm going to hazard a guess that they didn't! I will ask the question at some point I'm sure.

I was told at the start that 100% water proof concrete did not exist . I spoke to a rep at cemex . So I was surprised! . Best approach is manage water - don’t try and keep it out .

[Thorfun]

47 minutes ago, pocster said:

I was told at the start that 100% water proof concrete did not exist . I spoke to a rep at cemex . So I was surprised! . Best approach is manage water - don’t try and keep it out .

do you just have the one form of waterproofing?

[Pocster]

4 minutes ago, Thorfun said:

do you just have the one form of waterproofing?

No

i think from memory bco wanted 3 ‘things’ - so I have an external land drain around the build ( a pipe with holes in ? ) , plastic sheeting over the external walls below ground ( can guarantee it would of ripped ) . In my opinion these things are all pointless as can and will fail . Then of course the ‘real’ waterproofing of the dimpled  membrane on the walls and floor leading to an internal perimeter drain and then the sump .

Edited November 1, 2020 by pocster

[Bitpipe]

13 hours ago, Thorfun said:

 

 both the ground workers I've spoken to so far have said not to bother with waterproof concrete as standard concrete is pretty darn waterproof already. so with the Type C waterproofing it's possible that I wouldn't need it if it's not a warranty requirement. the other option is to use Type A and Type C if Type A is a lot cheaper than waterproof concrete. ultimately it wouldn't matter if the external tanking leaked as I'd have the internal membrane to fall back on.

 

Yes, concrete is inherently pretty waterproof and whatever add-mix is introduced just makes it more so. However shuttered concrete structures are not poured in one go and it's at the interfaces of cast sections that leaks occur and this  is where the WPC systems really add value 

 

Our contractor's formwork made provision for an inch wide & deep channel on the top of the slab kicker and on sides of each vertical section. These channels were then scrubbed clean of laitance with wire brushes and dried with blowtorches (we were doing this in September, so was occasionally damp). Into the clean dry channel went Sika waterbar,  applied with Sika mastic in advance of the next pour.

 

For penetrations, plastic sleeves of a larger diameter of the service were cast into the concrete, each with two rings of water bar applied. When we ran the services later, the gap between pipe and sleeve was filled with a non setting waterproof compound from Newton.

 

Finally mechanical expanding rubber bungs were used to seal all of the bracing holes and then sealed with waterproof cement.

 

Everything was photographed and sent daily to Sika and the rep came to site a few times to check progress.

 

THAT is what makes it properly waterproof and costs the time and money.

 

If you're investing in internal membrane then go for it and get a good warrantied job done and you should be fine. 

[Pocster]

8 minutes ago, Bitpipe said:

 

Yes, concrete is inherently pretty waterproof and whatever add-mix is introduced just makes it more so. However shuttered concrete structures are not poured in one go and it's at the interfaces of cast sections that leaks occur and this  is where the WPC systems really add value 

 

Our contractor's formwork made provision for an inch wide & deep channel on the top of the slab kicker and on sides of each vertical section. These channels were then scrubbed clean of laitance with wire brushes and dried with blowtorches (we were doing this in September, so was occasionally damp). Into the clean dry channel went Sika waterbar,  applied with Sika mastic in advance of the next pour.

 

For penetrations, plastic sleeves of a larger diameter of the service were cast into the concrete, each with two rings of water bar applied. When we ran the services later, the gap between pipe and sleeve was filled with a non setting waterproof compound from Newton.

 

Finally mechanical expanding rubber bungs were used to seal all of the bracing holes and then sealed with waterproof cement.

 

Everything was photographed and sent daily to Sika and the rep came to site a few times to check progress.

 

THAT is what makes it properly waterproof and costs the time and money.

 

If you're investing in internal membrane then go for it and get a good warrantied job done and you should be fine. 

Agree - this is the non diy way and must cost a good chunk of cash . If it’s all warranted then that is a massive added bonus . Diy v’s professional

 

Though I deliberately got my concrete poured as one to avoid any ‘gaps’ between the structure 

 

. ?

Edited November 1, 2020 by pocster

[Bitpipe]

21 hours ago, pocster said:

Agree - this is the non diy way and must cost a good chunk of cash . If it’s all warranted then that is a massive added bonus . Diy v’s professional

 

Though I deliberately got my concrete poured as one to avoid any ‘gaps’ between the structure 

 

. ?

 

Did you use ICF or shuttering? We did the latter and it would have been mega expensive to build shuttering for the whole structure, they created a form and rotated it round the structure so it took about 4-5 pours over two weeks.

[Pocster]

20 minutes ago, Bitpipe said:

 

Did you use ICF or shuttering? We did the latter and it would have been mega expensive to build shuttering for the whole structure, they created a form and rotated it round the structure so it took about 4-5 pours over two weeks.

I used the hollow concrete blocks . You lay dry , thread rebar in them - then do one mega pour at the end . It was high labour for me - but not particularly expensive.

[Bitpipe]

On 02/11/2020 at 09:38, pocster said:

I used the hollow concrete blocks . You lay dry , thread rebar in them - then do one mega pour at the end . It was high labour for me - but not particularly expensive.

 

Same principal as ICF I suppose - with traditional shuttering you're restricted to 6 linear metres per pour (or so I was told).

 

I guess then that the only join is interface between the vertical walls and the slab, did you do anything there or just rely on the internal membrane to catch any water that comes in.

[Pocster]

5 minutes ago, Bitpipe said:

 

Same principal as ICF I suppose - with traditional shuttering you're restricted to 6 linear metres per pour (or so I was told).

 

I guess then that the only join is interface between the vertical walls and the slab, did you do anything there or just rely on the internal membrane to catch any water that comes in.

Yep ; nothing special there . Perimeter drain would catch anything at that join .