Hairline cracks in lime cement plaster

The cracks appeared overnight.

Plastered exactly 8 weeks ago.

Setting is the chemical process in which cement and water form cement paste and subsequently cement stone. During this process, heat is released - the so-called [Hydradations] or setting heat. In short, as setting progresses, the concrete becomes harder. If the water dries out too quickly, it disrupts the setting, changes the volume, causes shrinkage, cracks. Therefore, with screed and plaster, do not ventilate immediately, but first keep the moisture inside the house.

Setting is the chemical process in which cement paste is formed from cement and water, and subsequently cement stone. Heat is released during this process – the so-called hydration or setting heat. In short, as setting progresses, the concrete hardens. If the water dries out too quickly, it disrupts the setting, changes the volume, causes shrinkage and cracks. Therefore, with screed and plaster, do not ventilate immediately but first keep the moisture inside the house.

Ok

Then I have to live with it.

I just want to be sure that the plaster is not hollow and is firmly bonded to the Ytong.

Simply tapping or is there a secret trick?

The contractor says everything is fine, I just want to check it myself once more.
Whereas a replacement would be a catastrophe.