Staining on external wall insulation system

[Heidi]

 We had a solid wall insulation system applied to the side of our house 6 years ago. It was rendered with a coloured silicone-based render.   This winter regular, rectangular staining has appeared on the surface. Would this be a cosmetic problem only - or the sign of something more fundamentally wrong with the insulation system and dampness trapped beneath? The system is supposed to have a 25 year guarantee. Grateful for any thoughts.

[Mr Punter]

It looks like the joins in the insulation boards.  The render should last longer than that but it is not uncommon to see modern renders discolour.  Can you get the contractor back?

[ProDave]

I suspect that is just irregularities in the render showing and it is just decolouration.

 

I am finding mine at 4 years old is starting to show discolouration from weathering which is moss / algae growing and I am experimenting with spraying it with a mist of water / bleach mix to kill it.

[Moonshine]

This is typical stains of this type of render (limed based render), when weathers, have a look at below.

 

 

The fact that its following the gaps in the insulation slabs indicates that its dampness coming from the masonry in the building, google the term "ghosting render''.

 

here is one example of the blocks showing through

 

Edited January 22, 2021 by Moonshine

[tonyshouse]

I am suspicious of actual gaps between the sheets of insulation allowing moisture to condense in the render in cold weather along the gaps, what insulation was used and what did they fill gaps with.

 

i have seen similar on aircrete blockwork where every mortar bed shows up darker due to being colder and wetter 

[Ferdinand]

I think a thermal photo would show up gaps in the insulation even better.

[nod]

2 hours ago, ProDave said:

I suspect that is just irregularities in the render showing and it is just decolouration.

 

I am finding mine at 4 years old is starting to show discolouration from weathering which is moss / algae growing and I am experimenting with spraying it with a mist of water / bleach mix to kill it.

Use Algicide mixed 4-1 

Let the rain do the rest 

[nod]

2 hours ago, Heidi said:

 We had a solid wall insulation system applied to the side of our house 6 years ago. It was rendered with a coloured silicone-based render.   This winter regular, rectangular staining has appeared on the surface. Would this be a cosmetic problem only - or the sign of something more fundamentally wrong with the insulation system and dampness trapped beneath? The system is supposed to have a 25 year guarantee. Grateful for any thoughts.

You will find this will clear in the summer months and not harm the render