High water content in external renovated limestone masonry wall

[stephanie]

Hi everybody,

I am doing a modelling of an external renovated limestone masonry wall with a ventilated cladding. The question I have is not related to the ventilated gap but more to the accumulation of water during the simulation of 5 years, and particularly on the internal face.

The insulation is a fibre glass (14cm). A ventilated gap and a cladding are simply considered by setting the wave radiation and rain values to 0.
In order to take into account the resistance to the water diffusion from the water resistive barrier, I add a 0,5 Sd to the external boundary condition.
For the internal boundary condition, I chose the EN 12026 with a normal moisture load. The HR for the internal air is the following. Note that it does not go over 60%.
For the external climate I chose an external climate file from Meteonorm (Millau).

The limestone masonry wall have been modelled with of “Krensheimer Shelly Limestone”(Fraunhofer database) and Bonding Mortar (University of Technology Vienna). Its total thikness is about 90cm. On the internal face there is a coating of Lime Plaster (Stoucco from Fraunhofer database).
The external fibre glass that is chosen is from the WUFI database: generic North America Database.

The simulation shows a very high water content in the internal coating. It varies between a 33 kg/m3 to a 230 kg/m3. (The density of the coating is 1600kg/m3). It is the same observation for the bonding mortar where the water content continuously increases from 33 kg/m3 to 70 kg/m3 after 5 years. (The density of the bonding mortar is 1350 kg/m3). Also, it is shown clearly that the water content is higher on the inner side as you can see in the graph.

First do you see any mistakes in this modeling?
If not, interpreting the results, are those high water content or RH values "plausible" ?

Without knowing that I guess we can draw as a conclusion that it is highly recommended to place a vapour barrier on the internal side.

Basically, I am looking for external outlooks as those values bother me.

Thanks
Regards
Stéphanie

[Christian Bludau]

Hello Stephanie,

are you sure, that the pink line is the mortar on the interior side? I´m asking, because according to the moisture storage function the internal coating has a water content of 250 kg/m³ at a relative humidity of 100%. So your 230 kg/m³ are 99% something. That would mean, that you have dew water conditions at the inside. Close to the interior surface the relative humidity should be about 60%, close to the room RH. Have a look on the RH close to the inside. I guess there might be an mistake in your boundary conditions. Did you set the heat transfer coefficients right? Inside it should be something around 8 W/m²K?

Christian

[stephanie]

Hello Christian,

Thank you for your reply. I actually made a mistake and i don't know why the heat transfer coefficients was at 0 and not at 7.7. Maybe I forget to save... I revised its value and the simulation works correctly with expected results. Small error of innatention, great consequence!

Thank you for your help.

Stéphanie