Spray foam insulation inside basement on walls with efflorescence – GreenBuildingAdvisor

My house was built in the early 1950. I’m planning on insulating my basement. My preference would be to excavate the foundation and apply exterior rigid foam, but the engineer that I’m working with says the following:

1) It would be substantially more expensive to excavate the house then doing interior spray foam

2) He and a second engineer that I talked to insist that I won’t have an issue with dampness from foundation entering the rim joist and sill plate and condensing against the cold wood due to the spray foam preventing the house heat from keeping the wood warm.

I’m planning on adding rigid insulation on the exterior from about a foot above my rim joist to the ground level or maybe even a foot below ground level and then protecting it with a faux wood finish to help keep the rim joist and sill plate warm. My preference is to go with R-20 rigid exterior insulation. While it might be overkill at this point, I’m not very optimistic about future energy costs, so I think it’s sensible from a long term perspective. Having said, at this point, my thinking about the amount of R-value I need to keep the rim joist and sill plate warm is really a WAG 

In the meantime, my basement wall has some efflorescence although I haven’t seen any water mitigate through the walls into the basement. Nevertheless I’m concerned about covering the walls with spray foam if my walls are damp enough to cause efflorescent. Should I be concerned about this?

Secondly, one engineer mentioned sealing the walls with radon seal, which has the additional benefit of preventing further efflorescence. It would be sprayed on the interior of the walls. It would involve removing paint from the inside of my basement walls. I’m considering renting a dry ice blaster for that task. Do this sound reasonable?