Securing flint to ICF

[Bancroft]

We're planning to have timber cladding around the main part of our ICF build with a 300mm flint 'splashback' on the lower part of the wall (between the bottom of the timber and the ground level).

 

What is the best way to secure/cement the flint pieces to the exterior of the ICF wall?

 

I'm imagining some sort of scrim secured to the ICF which the mortar can then be worked into - but how is the scrim securely attached to the ICF?

[JohnMo]

Foam or woodcrete ICF?

[Nickfromwales]

With an EPS system I suspect you'd need a form of mechanical fixing at (or above) a certain kg/m2 loading, so perhaps you'll end up fixing a 6 or 9mm cement board to the structure and then using tile adhesive to attach the flint to the CB.

 

If this is a woodcrete then maybe you can parge with cement slurry, tank, and go for the above fixing method. 

[Russell griffiths]

Will this create a large shelf that you will need a flashing over. 

on an eps block I rendered onto the eps with a waterproof render with mesh included, then left the surface very rough. 
then laid natural stone bedded in exterior slip adhesive and stuck back to the render with the same slip adhesive, stainless screws and stainless brackets bedded in every third course. 

[Bancroft]

  On 10/04/2025 at 10:54, JohnMo said:

Foam or woodcrete ICF?

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Foam

[Bancroft]

  On 10/04/2025 at 12:07, Russell griffiths said:

stainless screws and stainless brackets bedded in every third course

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Was this to help take some of the weight as you built up and add additional purchase points?

[Bancroft]

  On 10/04/2025 at 11:18, Nickfromwales said:

tile adhesive

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Would tile adhesive be sufficiently strong/permanent for an exterior subject to rain/snow/sun/freezing?

[Russell griffiths]

  On 10/04/2025 at 13:22, Bancroft said:

Was this to help take some of the weight as you built up and add additional purchase points?

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I don’t think they were needed at all, but did it anyway. 

[SteamyTea]

Ask @Onoff

 

There is a small amount of info here.

 

 

[Bancroft]

Talking with our architect today I mentioned this issue and he pointed me towards a product called Surecav.

 

They have used it with a number of different external materials including stone and flint and seem happy with it.

 

Anyone else got any experience with this product?

 

https://www.surecav.co.uk/flint/

 

[jack]

  On 11/04/2025 at 13:53, Bancroft said:

Talking with our architect today I mentioned this issue and he pointed me towards a product called Surecav.

 

They have used it with a number of different external materials including stone and flint and seem happy with it.

 

Anyone else got any experience with this product?

 

https://www.surecav.co.uk/flint/

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Others on BuildHub appear to have used Surecav: https://forum.buildhub.org.uk/search/?q=surecav&quick=1

[Nickfromwales]

  On 10/04/2025 at 13:24, Bancroft said:

Would tile adhesive be sufficiently strong/permanent for an exterior subject to rain/snow/sun/freezing?

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Yup. Have a look at a bag and you’ll see tiling outdoors is completely permissible and commonplace worldwide.
 

The product just needs to be cementitious, and flexible, and primed according to MI’s. 

[Nickfromwales]

  On 11/04/2025 at 13:53, Bancroft said:

Talking with our architect today I mentioned this issue and he pointed me towards a product called Surecav.

 

They have used it with a number of different external materials including stone and flint and seem happy with it.

 

Anyone else got any experience with this product?

 

https://www.surecav.co.uk/flint/

 

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That obvs pushes the stone course out and then requires a suitable extension to the foundation system to accept the load. 
 

A low profile faux version would be affixed to the structure, bonded to cement boards mechanically fixed / bonded on the external facades, so would be simpler and cheaper perhaps, but down to the product you eventually decide upon.

[Russell griffiths]

I thought you mentioned 300mm high, if so you going to push your stone out from the icf by loads if you use surecav, sounds very OTT for just a strip at ground level and below finished floor height, surecav is predominantly used on timberframe. 

[BotusBuild]

I am just in the midst of stone cladding onto Nudura (EPS ICF).

 

First it was screeded using Duravit and embedded mesh, and then roughed up to allow the adhesive to key into it. This seems to be the essential step for any "hard cladding" such as stone panels or flints or the stonework as pictured above by Russell.

 

The  adhesive (Sicher Kerami plus) came in 25kg bags to be mixed onsite with added water. It's much like tiling a wall - apply adhesive to wall, trowel in vertical grooves, "butter" the stone cladding, affix to wall. Above 2.4m you have to mechanically fix these as well

Result:

 

For flints I suspect the mix would be a little thicker and you would want to do the bottom row, let it set off and then do the next row.

[Tosh]

I screwed backer board to the battens. This maintained an air gap at the bottom to ventilate the cladding above. Then fixed a steel mesh to stop 'things' getting up behind the cladding. I screwed temporary battens to support the slate and provide a consistent line (you can just see this on the left of the downpipe) then removed them later. My slate panels had clips prefabricatred into them for a mechanical support, not technically necessary in my case but I still found them useful. Ignore the downpipe connection, that was a temp setup whilst we waited for the correct pieces from lindab to arrive.

 

 

[Bancroft]

  On 11/04/2025 at 17:39, Nickfromwales said:

That obvs pushes the stone course out and then requires a suitable extension to the foundation system to accept the load.

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Wouldn't have thought the load would be an issue as we're only looking at 300mm but I was wondering about how deep the battens for the timber cladding above would need to be in order to ensure the flint was inboard of the cladding.

 

  On 11/04/2025 at 17:39, Nickfromwales said:

A low profile faux version would be affixed to the structure

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Do you mean faux flint?  We're looking at real flint as a first choice but I am aware that flint brick slips are available and might be an option.

[Bancroft]

  On 11/04/2025 at 18:01, Russell griffiths said:

if so you going to push your stone out from the icf by loads if you use surecav, sounds very OTT for just a strip at ground level and below finished floor height

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I haven't looked closely at the depth of Surecav so thanks for that heads up.

 

Given the choice, I'd rather go a little OTT and make sure everything stays stuck to the building rather than find it peeling away (or, worse, pulling the ICF foam away from the concrete).

[Russell griffiths]

  On 14/04/2025 at 09:06, Bancroft said:

I haven't looked closely at the depth of Surecav so thanks for that heads up.

 

Given the choice, I'd rather go a little OTT and make sure everything stays stuck to the building rather than find it peeling away (or, worse, pulling the ICF foam away from the concrete).

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If this is a section below finished floor level you shouldn’t need any form of waterproofing as it’s all below dpc, 

using real flint will stick you out 100 mm plus from the icf, you will need some serious counter batten and batten to get the cladding to overhang. 
 

using a fake stone will give you a more consistent depth and thinner profile. 
 

have you considered rendering this bit, it could save a few grand in the build process. 
 

I can see the attraction of the flint if you are doing a wall of it, but just the splash zone at ground level seems an expensive method for a strip at ground level. 
 

depending on what icf you use you will not pull the eps off the concrete, it should be very secure, nudura you actually need to destroy it to get it off. 
 

I would waterproof render onto the icf, reinforcement mesh, rough up the render, then fix the stone/ flint with slip bond adhesive, pointing as you go.