If trying to airseal an old, not-perfectly-straight block basement wall what's the best way to go about it? I considered applying some rigid foamboard but the fact that the wall has a 1" bow makes that extremely difficult. It's also kind of tough to get good adhesion on an old wall like that. I've been told that I could get good adhesion for a skim coating if I first etch the wall. Would this be a good strategy? Has anyone else ever dealt with this situation? Thanks.

Do you mean insulate or airseal? Most of the basement would be below ground and not need much airsealing. The outside above ground shoud be sealed or stuccoed or something, you dont want to try and stop the air with foamboard after it is already in your basement.

A surprising amount of air leakage can come in through soil and block foundations DO need to be air-sealed to keep soil gases out.

If there is reasonable above-grade exposure on the block wall (say a half-meter), and reasonable roof overhangs, you can air-seal the interior with poly sheeting.

But that may interfere with some of your other goals here. Are you planning to insulate and finish this basement?

No chance of finishing it. I just want energy efficiency.

Do you think a skim coating would be the best approach?

If you are going to skim coat it anyway, maybe use a product like Dryvit's Primus. This is the product that stucco guys use to adhere foam to the wall prior to stucco. It is also sometimes used as the base coat.

Lay the Primus on thick with a notched trowel and then lay eps foam board into it. Should give you seal and R at the same time.

Prep the wall with a steel brush and or etch would help.

Posted By strategery on 18 Jan 2014 02:26 AM
No chance of finishing it. I just want energy efficiency.

Do you think a skim coating would be the best approach?

Air sealing would only be the first part then- how do you intend to insulate?

Here in sunny Minnesota we do a lot of mechanical work in basements before they are finished. Many home in Minneapolis/St. Paul are well past the century mark but people want to make them safe and efficient. We have found the best way to seal and insulate most of them (many being hand laid stone) is to frame and foam them. 2 lb. foam will cover a lot of sins.

We often demo the old floors, install plumbing and radon piping, the vapor retarder, rigid foam, PEX tubing and concrete with foam on the walls up to the most critical area; at the rim joist. Just about radon and vapor-proof construction though not cheap of course. The foam must be covered with sheet rock for fire.