Check the strengths of your Building Materials.
I would make the masonry block the strongest as you seem to want this to always be continuous.
Then the heat insulation a bit weaker and the plaster even weaker still.
You could differentiate between the internal and external plaster if you want but this shouldn't matter as they are separated by the stronger masonry block.
In this case make the external plaster weaker than the masonry block, the heat insulation weaker and the internal plaster the weakest.
This means of course you need two separate materials for the internal and external plaster.
The second mode is the one you want - Legacy mode turned off.
Otherwise you will not see the effects of the priority strengths in the 3D window.
Barry.
One of the forum moderators.
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