surface coatings -

[Sandberg]

Hello,

I am simulating the drying capacity of a wall subject to abundant water ingress in the past. The question being asked is how long the wall will take to dry.

The wall is rendered with a portland cement mix and coated with several layers of different types of paint (acrylic and oil based). I have simulated the paint layers in the assembly with a 1mm acrylic render (sd-value=1). In the surface conditions I selected "no coating" for the sd-value and an adhering rain factor dependant on the element exposure, because the wall is exposed to rain.

I then wanted to campare the same wall in the same conditions but with a lime based render and a bretahable paint (sd-value = 0.1). This is thought to be an improvemnt which will allow the wall to dry more quickly. This time I did not add the paint as an element in the assembly (wufi does not have coatings in the materials library) but I simulated the paint in the surface conditions as acrylic paint (sd-value=0.1), and an adhering rain factor dependant on the element exposure.

Surprisingly, the wall will take longer to dry to the desired moisture content.

Is this becasue the two models are not really comparable, given that the coatings were modeled in different ways?
What is the correct way to model the coatings?

In "surface conditions" there is an option for an impermeable coating sd-value=1 but this options also comes with a note saying "without driving rain". What does this mean? that rain is not accounted for? I want to include the rain effect as the wall is fully exposed.

[Christian Bludau]

Hi,
right, these two ways can not be compared directly.
You can either build them all in as a layer for example derived from a membrane. This way no rain will be absorbed by the wall, but you can compare the drying potential. Or you take account for the coating like described in our tutorial about the water-repellent treatment:
https://wufi.de/en/service/downloads/#w ... _treatment
In there a layer of the surface material is split of and modified. Please keep in mind, that a painting also will affect the a-value (probably it will not be easy to get this values for the coating). That would be the more realistic way.

The sd-value in the surface coefficients only affects the diffusion, so the full amount of rain can pass and the surface will absorb it - but drying is reduced by the sd-value.

Christian