As you can probably guess, we've had a prefab garage built ontop of a concrete base. Inside i've soundproofed the walls and has about 6-7inches of different thicknesses and densities etc etc. There is a concrete screeding round the edges between the wall and the floor. BUT, somehow even through all the soundproofing and screeding, there is a damp patch in the corner, this is causing all the external rockwool to be covered in condensation.
We've tried buying some conrete floor sealant and painting that across it, we've left a dehumidifier in there for a week and dried it all out, but only for it to come back again in just a week. If it is any importance, outside of the building, the edge of the conrete has cracked off due to the movement in timber around the edge, whether that could be contributing i don't know.
Basically, we need to get rid of this damp patch in the corner so that we can get plasterers in to finish off the job. Then we're goign to lay a membrane across the concrete, lay carpet underlay, and then carpet and finish with coving.