Sealing ICF block to concrete slab joint

[ICF Self Build Northum]

Does anyone have any experience of sealing their ICF block to the concrete slab joint?

 

As things stand, our external construction is up and, at ground level, we have some moisture coming in at the ICF <> slab joint. We've specified UFH internally and a further DPM is to be put down inside the property and our architect has said the moisture won't be an issue (i.e. we'll end up with a wet slab as opposed to dry slab). But I wondered if anyone else has experience of using a product like Blowerproof Liquid to add an extra level of protection?

 

https://www.ecomerchant.co.uk/liquid-blowerproof-brush-paint-on-airtight-sealing-membrane-5kg.html

[Nickfromwales]

Hi. Which ICF system have you used?

I'm on 2 different ICF projects where moisture at the ICF / slab junction is recurring. It's because the rain screen on the outside of the ICF has not been applied yet, therefore the rain comes under at the DPC ( capillary action, plus the DPC acts like a tray which harvests and retains the rainwater ) and makes the slab look 'damp' at the edges. This is to no real detriment at this time, and I think your architect is completely right.

Is the slab TOC ( top of concrete ) your FFL ( finished floor level ) or are you to have a membrane and a screed atop the slab? The above instances I refer to are passive raft foundations where the TOC is FFL less floor coverings. Bottom line is that until you render / other outside to form a rain screen to ground, you will gt that problem. It will be hugely reduced at that point and the build will typically cope from there on with whatever moisture fluctuations occur.

Don't waste your money on liquid membranes etc for the whole floor, but maybe just applying at the internal corner at the periphery will settle your mind. Personally I think you're worrying about nothing, but we'd need to see sectional drawings of the structure and the topology of the site to give any further quality information to you. It seems strange however, as normally the slab would be on insulation and a damp membrane already, if there is UFH and a ( heated ) screed to go atop? If the subfloor is to "end up as a wet slab vs a dry slab" then I would be concerned about the cold bridging more than the damp!!

If you can post some sectional drawings that would help.  

[ToughButterCup]

11 hours ago, ICF Self Build Northum said:

Does anyone have any experience of sealing their ICF block to the concrete slab joint?

...

 

Yes.  I asked and was told there is no need to seal it.

Our house has wooden cladding. Before that was put on, some areas had no clearance at all between the MOT1 and the DPC. So,  a bit of damp came in - and promptly left when the sun came out. When I eventually reduced the MOT1 to the correct level and put the cladding on, it's drizabone.

 

After 4 years, I still need to sort out the back step: there's gravel to just above the DPC - a bit of damp comes in now and then when there's driving rain from the South west , nowt to worry about. Disappears straight away - sun cooks it.

 

[ICF Self Build Northum]

On 15/04/2021 at 10:01, Nickfromwales said:

Hi. Which ICF system have you used?

I'm on 2 different ICF projects where moisture at the ICF / slab junction is recurring. It's because the rain screen on the outside of the ICF has not been applied yet, therefore the rain comes under at the DPC ( capillary action, plus the DPC acts like a tray which harvests and retains the rainwater ) and makes the slab look 'damp' at the edges. This is to no real detriment at this time, and I think your architect is completely right.

Is the slab TOC ( top of concrete ) your FFL ( finished floor level ) or are you to have a membrane and a screed atop the slab? The above instances I refer to are passive raft foundations where the TOC is FFL less floor coverings. Bottom line is that until you render / other outside to form a rain screen to ground, you will gt that problem. It will be hugely reduced at that point and the build will typically cope from there on with whatever moisture fluctuations occur.

Don't waste your money on liquid membranes etc for the whole floor, but maybe just applying at the internal corner at the periphery will settle your mind. Personally I think you're worrying about nothing, but we'd need to see sectional drawings of the structure and the topology of the site to give any further quality information to you. It seems strange however, as normally the slab would be on insulation and a damp membrane already, if there is UFH and a ( heated ) screed to go atop? If the subfloor is to "end up as a wet slab vs a dry slab" then I would be concerned about the cold bridging more than the damp!!

If you can post some sectional drawings that would help.  

 

Thanks for your response Nick. We're using the Amvic block system. The ICF has been built straight off the top of the raft foundation. And I think you're right - we haven't applied the skirt of render or the larch cladding yet (or the rainwater goods) so all of the water landing on the building is dripping onto the DMP and being directed towards the 'trouble spots'.

 

The slab isn't the finished floor level... internally, we have another DPM, 100mm of PIR and a 55mm poured screed to go down (with UFH on top of the PIR). It does feel like I'm worrying about nothing, but want to get some extra opinions before we move beyond when we could have done something about it. Feels like the option of paining the waterproofing on the inside joint to minimise moisture ingress could be a good option. A bit belt-and-braces without going over the top.