ICF RENDER

[Moggaman]

Hi. Looking for advice. Sorry for long post.

13 years ago I built an icf house. At the time I put on a Weber material with mesh worked into it, then more Weber material, a primer and then an acrylic finish. I wasn’t around much when it was being applied. It was meant to be about 10mm thick .
I have had many issues over the years with this render. The ICF has plastic webs, beams running through the wall from one face to the other and the render on the south and west side Is cracking vertically and horizontally along these . I investigated many times and it appear that there is only 5mm of render in total on some of these walls. I would say that the polystyrene bulged a little when the walls were being poured and that the walls were not rasped back before applying the render. Anyway , that’s the background. The result is that I have a fair amount of water infiltration in bad weather. I am planning to sell the house as I am moving to another (non ICF) house. I want to deal with this problem . I need to sort the west and south elevations. I had some plasterers and a contractor look at it and the solution we came up with was

- leave existing render in place

-fix galvanised metal mesh to the walls using the plastic webs as anchors.

- scud , scratch and finish wall with sand , cement render ….

I know that people say that sand cement render is not suitable for ICF.. I assume that is mainly because it is too heavy to bond to the polystyrene.

if I have the metal mesh in place , that would guard against that issue?

thanks for reading and looking forward to your response .

 

 

[Conor]

You have to take the render right off, rasp, and put a proper render product on, e.g Sto or k rend. There will be a base coat, mesh, another base then the coloured top coat. It sounds like your render wasn't put on properly.

[ToughButterCup]

10 hours ago, Moggaman said:

...

if I have the metal mesh in place ,

...

 

I'm no expert, but wouldn't the metal do what it always does with an etching compound (sand-mortar-water) and simply rust? And then weep through to the surface? And stain?

 

With  a bit of luck @nod will be along in a bit..... 

[Moggaman]

10 hours ago, Conor said:

You have to take the render right off, rasp, and put a proper render product on, e.g Sto or k rend. There will be a base coat, mesh, another base then the coloured top coat. It sounds like your render wasn't put on properly.

Thanks Conor. I realise that this is the standard way with ICF but I am wondering why my option would not work?.. forget about potential staining .. won’t the mesh ensure the render stays where it is put on.. it reinforces it.!. Is there a flexibility issue?

[ProDave]

I have my own theories about thin coat render on well insulated buildings, having got my own issues.

 

Sand / cement render seems to work okay on normal masonry buildings.  I am convinced part of that is the buildings leak heat, and the outer surface of the building never goes below 0, even here in the Highlands, where temperatures well below 0 are normal in winter.  I also observe that a lot of cement rendered buildings also absorb a lot of moisture in driving rain, and the render changes colour because it is wet.

 

Take away that "leaking heat" factor and cement render on a wall that is likely to absorb water and then freeze when the temperature goes below 0 without the heat leaking out to stop it, and the render will fail.  I note garden walls here that have been rendered, the render is falling off after a winter or 2, I am convinced because there is nothing to stop the render freezing.

 

So assuming an ICF building is well insulated I fear cement render would fail in a hard winter.

 

So ANY render used on a well insulated house has to be totally waterproof or not capable of absorbing water that can then freeze.  I think that is at the heart of thin coat render failures where I suspect in our case, the outer layer has not been completely waterproof.

[Moggaman]

3 hours ago, ProDave said:

I have my own theories about thin coat render on well insulated buildings, having got my own issues.

 

Sand / cement render seems to work okay on normal masonry buildings.  I am convinced part of that is the buildings leak heat, and the outer surface of the building never goes below 0, even here in the Highlands, where temperatures well below 0 are normal in winter.  I also observe that a lot of cement rendered buildings also absorb a lot of moisture in driving rain, and the render changes colour because it is wet.

 

Take away that "leaking heat" factor and cement render on a wall that is likely to absorb water and then freeze when the temperature goes below 0 without the heat leaking out to stop it, and the render will fail.  I note garden walls here that have been rendered, the render is falling off after a winter or 2, I am convinced because there is nothing to stop the render freezing.

 

So assuming an ICF building is well insulated I fear cement render would fail in a hard winter.

 

So ANY render used on a well insulated house has to be totally waterproof or not capable of absorbing water that can then freeze.  I think that is at the heart of thin coat render failures where I suspect in our case, the outer layer has not been completely waterproof.

Interesting theory 

[Moggaman]

On 05/04/2022 at 18:13, ProDave said:

I have my own theories about thin coat render on well insulated buildings, having got my own issues.

 

Sand / cement render seems to work okay on normal masonry buildings.  I am convinced part of that is the buildings leak heat, and the outer surface of the building never goes below 0, even here in the Highlands, where temperatures well below 0 are normal in winter.  I also observe that a lot of cement rendered buildings also absorb a lot of moisture in driving rain, and the render changes colour because it is wet.

 

Take away that "leaking heat" factor and cement render on a wall that is likely to absorb water and then freeze when the temperature goes below 0 without the heat leaking out to stop it, and the render will fail.  I note garden walls here that have been rendered, the render is falling off after a winter or 2, I am convinced because there is nothing to stop the render freezing.

 

So assuming an ICF building is well insulated I fear cement render would fail in a hard winter.

 

So ANY render used on a well insulated house has to be totally waterproof or not capable of absorbing water that can then freeze.  I think that is at the heart of thin coat render failures where I suspect in our case, the outer layer has not been completely waterproof.

Even if water got into a 20mm sand cement render , it’s gonna have a tough time cracking it ?

[Simplysimon]

58 minutes ago, Moggaman said:

Even if water got into a 20mm sand cement render , it’s gonna have a tough time cracking it ?

 

does it matter, you're selling it