We are in the process of conditioning the basement of an 1800 year built barn in Massachusetts.  Currently the basement is an exposed dirt floor ( actually the soil is more like sand ).  We’re putting a 15mil vapor barrier down followed by 2″EPS foam ( Crete Heat ) with 5/8″ pex tubing for an in-slab radiant system.  Concrete slab will be  4″ on top of that.  

The foundation, being fieldstone, is moist and despite proper gutters and grading outside, still allows moisture on good rains. 

As we prepare to underlay the vapor barrier, we are struggling to agree on the best way to handle the perimeter – both in making the seal of the vapor barrier against fieldstone and whether or not it should even be sealed. 

Anyone have any thoughts or experience with this type of application?  

Thanks!!