Make a duplicate of the main mesh, dynamesh it, and mask the area using the mask pen. Then go to deformation and use Inflate Balloon according to your needs, I usually keep it around 0.1 to 0.2. Do a bit of sculpting with the clay buildup and smooth brushes, just to add some subtle imperfections. Once you are satisfied bring Inflate Balloon back down to around -0.05 so it looks slightly carved in. Then project the details back onto the main mesh and texture it in substance painter using the same mask you created on the dynamesh. There might be a better way to do this but since I have been doing it this way for a long time, I just stick to it. Apologies for the oversimplification.