WUFI BIO - mould within EPS?

[fostertom]

I understand that WUFI Bio was developed to predict mould risk on internal surfaces and maybe on surfaces of hidden cavities.
I think I heard that it can also be used to predict mould risk within more solid parts of the wall buildup - is that correct?

What about EPS e.g EPS as External Wall Insulation with acrylic render? In that application, EPS has v high moisture content and often liquid condensation, which apparently isn't a great problem as long as it dries out.

Do I need to worry about mould forming on surfaces within the many air cavities in EPS? Can WUFI Bio assess this? What about, similarly, things like wood fibre, which is full of micro-cavities?

[Daniel]

Mould growth within the EPS structure can not be excluded completely (under very extreme boundary conditions) but is really very unlikely.

Normally no spores can get into the EPS structure.

WUFI Bio is definitely not valid to predict such a type of mould growth with the current input data.

But in fact the only thing required would be lab tests describing the minimum temperature and RH conditions and the time period which is necessary to start mould growth in EPS. But I fear such information is not available yet.

However a WUFI Bio evaluation for example with substrate class k (which is representative for toxic mould species) should still be on the save side concerning the growth risk!

Daniel

[fostertom]

Mould growth within the EPS structure can not be excluded completely (under very extreme boundary conditions) but is really very unlikely.

Normally no spores can get into the EPS structure.

Is that because EPS provides no food for mould? Would you give the same advice for wood fibre insulation in the outer layers of EWI i.e. just behind the external render finish? Mould "really very unlikely"?

[Daniel]

Of course there is a big difference between foam insulation and mineral or even natural fibre insulation.

The EPS structure is tight for spores and dust, vapor retarding and doesn't provide nutrients to the microorganisms.

Natural fibre is nutrient itself. It is vapor permable and contains as well spores as other particles from air. So here the risk higher by far.

Daniel

[fostertom]

Thank you.

Studying this, but not confident I'm getting good results, about moisture levels close behind the render. So I am looking for good data for proprietary renders for EPS EWI.

The only candidate in WUFI database seems to be Sto DecoSil, which is obsolete on Sto website, and hard to guess what it might be similar to, amongst current products. Is there any database product that I'm overlooking?

Both Sto and Alsecco give partial data, wondering how to make a better 'custom' database product out of these various sources.

[Daniel]

If you choose a redner close to the one you want to use it should be sufficient to adapt A- and µ-value. Based on the A-value the liquid transport can be approximated. Please check also the manual to do so...

Daniel