Moisture damaging scotia

[Spiritlisa]

I have had a problem with my scotia in the front room. The pictures attached show what the issue is. The wall is below a bay window - it is an external wall at the front of the house. I have had the wall checked for damp by a special and there are no signs of damp in the walls. The same has happened on an area in another room though not by an external wall, but by the wall next to the fireplace. I know a builder who is at an absolute loss as to what the issue is. I've even had slugs coming under the scotia in the front room, hence salt appearing in one of the photos. This started a couple of years ago and I thought it was sorted as I had someone fix the drain in the front garden as we thought that might have been the cause, but the drain is fine and not on the same side as the most recent damage (the first photo). There is also some damage to the join in the laminate flooring aa can be seen in tje second photo. Does anyone have any ideas? Also appealing to @pigletjohn if he is around.

That's a damp problem

Thank you for responding! So that would mean it is coming through the floor? There was no reading of damp in the walls. Or is it something that can be solved with better ventilation into the rooms?

Although many people say that one gets damp when there is not enough ventilation, it is my experience that there is usually another cause for it. Keeping the room in which the problem exists does help a bit but will not resolve the issue.

A cracked window seal, a blocked drain etc.

They can be a real PITA to find and deal with.

Until you do find the cause the only remedy is to paint over it, best with an anti-fungal paint. It will come back again but this may delay it a bit.

Thank you. I'm at a loss as to how to find the cause: the drain has been fixed and no other obvious causes. It is also not affecting all scotias - one is in a different room and only in one section of that room! Thank you SO much for your help though. I am really grateful.