Damp Proofing Garage garage Floor to Prevent Damp Coming Thorugh

[Salmonboy]

I have a garage which is attached to the main house, this is being used as a utility room/storage. Recently I noticed hard black ball shapes coming from the carpet, I looked into this and formed the opinion this was damp. I pulled up the carpet tiles and noticed that there was chipboard underneath which was damp and rotten, this chip board was placed directly on the main garage floor.
I have recently pulled up the capers tiles and wooden chip board so that I just have the original floor.
I have been looking at how to damp proof this, I an happy having the original floor however on looking at various bits online do not know which was to go.

Should I buy KA tanking slurry and a self level compound and paint this?

ShouldCan I/should I buy a paint which I can paint straight on the floor which also acts as a damp proof membrane such as https://www.toolstation.com/shop/Roofin ... fer/p33714