External paint on lime render

[pdp]

External paint on lime render
I am comparing no paint, Keim Soldalit paint and Dulux Weathershield paint onto lime render with solid brick wall using the following data
Soldalit Sd = 0.0106m (from product literature)
Weathershield vapour resistance 4.1 MNs/g (from BBA certificate), using conversion tables Sd = 0.82
To simulate the paint finish I included the SD value in the external surface transfer coefficient and switched off the adhering fraction of rain. Will this give a realistic value?
I read in the NBT (natural building technologies who supply Pavadry in UK) IWI moisture risk analysis protocol not to use the Sd value to simulate paint, and instead to use the Fraunhofer 'resin finishing coat' adjusted to a thickness of .001m. I tried this and changed the Mu values but got different results?

Which is the most reliable method? Are there other suitable methods knowing the Sd or vapour resistance only?

Thanks

[Daniel]

The question is, if rain water absorption is really zero... if so you can simulate with an surface sd value. Due to the grid resolution for very fine grid elements and the averaging between the two border gride elements between two materials, the sd value is not exactly the same like thickness * µ-value - but can be maringlly lower. However this has normally only a neglible influence.

If you simulate with rain water absorption it is important to distribute liquida water absorption properties and diffusion ressistance in a similar way. A concentration of the additional sd value directly to the surface reduces drying potential compared to water absorption. So for renders a thin surface layer with the properties is always better. For paintings also an sd value should be OK, as the layer in reality is also extremely thin.

So:

1. no rain, extact sd value: surface sd
2. with rain: thin surface layer with appropriate liquid transport and µ-value.

best regards
Daniel