Vapor Barrier on cellar dirt floor
Hello, my situation is ca. 1770 house in Mass. with rubble foundation (joints only partially chinked), and dirt floor. To reduce water vapor infiltration, I have so far:
1. Installed 30mil MDPE 'pond liner' on top of geotextile (the latter to protect MDPE from punctures due to stones underneath). This barrier is fitted around chimney bases, pump sump, and MANY lally columns. Joints are lapped by about 6" and poly runs up foundation walls 6-12".
2. Installed dehumdifier, draining into sump. Not surprisingly it costs about $500/yr in electricity when set to 60% RH.
Ok, now my question: to further lower water vapor entry, what is the next most important step to take, for example:
- Seal the edge of MDPE to the rubble foundation wall, perhaps with a butyl-adhesive based membrane like "Ice & Water Shield."
- Seal the lally column openings, maybe with rubber flange typically used for plumbing stack going through a roof.
- Apply a vapor retarder to the rubble foundation.
Many thanks for your advice.