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efflorescence and rigid board insulation question

J2D2's picture


I am re-finishing/insulating my basement in a 1930 home in Zone 4 (Pacific NW). I am planning to do it as follows from foundation to interior which meets local building code: Basement Concrete Foundation Wall  >  1”XPS Rigid Board(Pink Owens Corning)  >  2x4 Studs against the XPS  > ROXUL insulation in stud cavities  >  Sealed Poly Vapour Barrier  >  Drywall.
There is evidence of white efflorescence on the basement walls indicating that there may be or has been in the past moisture seepage. There have been no flooding events. Being a 1930 house, the foundation is not waterproofed. 
When i pulled out some walls from a previous renovation from the 90’s there was poly vapour barrier against concrete foundation wall, 2x4 studs with some loose foam board, another layer of poly vapour barrier and then drywall. The foundation wall was damp but there was no mold or rot. 
I have a few question i am hoping someone can help with:
1. Given the efflorescence, is it required to clean off and seal with waterproofing paint on the interior (Xypex or Drylock)? Excavating and waterproofing exterior is not an option. 
2. Or can i just install XPS board directly against the wall? Or will that trap moisture and possibly lead to mold? 
3. When installing XPS does it require a seal on top and bottom edges using foam spray? (Joints will be taped) Should it be airtight or is it ok/better to let some air flow in behind XPS board to let foundation wall dry out? 
Any feedback greatly appreciated.

Do keep in mind that there's (post #215779, reply #1 of 2)

Do keep in mind that there's nothing there to mold, so long as you keep wood, paper, etc, away from the wall.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Why can't the outside of the (post #215779, reply #2 of 2)

Why can't the outside of the basement wall be sealed and a sumpump with drain tile be installed?  That is the correct way of doing it.


Once moisture comes through the wall your framing, insulation, and drywall are no longer protected.


Finished insulated  basements have a tendency to be cool.  Cool dark and dampness do not mix well.