I'll be constructing a below-grade cedar closet with 2 exterior walls involved over stuccoed cinderblock.

Should I mount a plywood sheathing backing to the cinder block first? (Not planning to frame and insulate first)

Is general construction adhesive the best choice? Or is there a reason to use paneling adhesive?

Unless the stucco is exceptionally smooth, I would sheath it first to give a consistent backer.

Pretty much any construction adhesive like Liquid Nails should be fine.

Edit to add: Be REAL sure you have moisture under control before doing anything else. Don't know where you are but here "below grade" and "concrete block" equals leaks.

Thanks! Those were my exact thoughts as well. I appreciate the confirmation.

Yep need some more information in order to make a proper recommendation.

What state do you live in?
Are the cinder blocks hollow? Or are they filled with foam insulation?
Are the painted/sealed on the outside? What about the interior side of the block?

I would not install anything against a cinder block wall below grade without some moisture mitigation solution first and that solution would depend on the answers to the above questions.

I wouldn’t put untreated wood in direct contact with concrete regardless how well the outside is sealed. The different thermal masses is very likely to produce condensation. I would install 1 x 2 pressure treated furring strips at a minimum.

quote:

Originally posted by DaveL:
I wouldn’t put untreated wood in direct contact with concrete regardless how well the outside is sealed. The different thermal masses is very likely to produce condensation. I would install 1 x 2 pressure treated furring strips at a minimum.

I'd been considering that, and will do as suggested. It'll work well to leave some space above and below open for air flow.

Almost certainly hollow block, sealed on outside, stucco on inside.

I thought I had heard not to use pressure treated wood indoors due to health risks from the chemicals used?
Is that false?

quote:

Originally posted by WaterburyBob:
I thought I had heard not to use pressure treated wood indoors due to health risks from the chemicals used?
Is that false?

The only issue is if the house were to burn. That’s also why they don’t recommend burning pressure treated material. All of your sill plates in your home if built on a slab and the board that sits atop your foundation wall if using a basement or crawl space (mind went blank and can’t recall the name of the board) are pressure treated. Essentially any wood that will remain in contact or does not have a barrier between will be pressure treated.

As to the original post without knowing anything else about your setup I would recommend lathing out the wall at a bare minimum.

Consider sealing the wall first.
Has it been painted or is it still bare stucco?
If never painted, something like UGL Dry-Loc would be good insurance.

When you say "below grade" do you mean as in "basement?"

If so: You must put a vapor barrier between the concrete or cinder block and whatever material it is with which you line the inside (wood, plasterboard, etc.)

If you want to avoid that closet, which will be dead air space, becoming a humidity-trapping space out of which moisture will condense and create mold (ask me how I know), you should also insulate those exterior walls.

You can accomplish both vapor barrier and insulation with solid foam panels. Seal the seams with Great Stuff.

N.B.: If part of the space in question includes a rim joist there will probably be fire code rules you'll have to follow for insulating that.

The outside walls of my Man Cave, insulated, sealed, and with 1x2 strips attached for securing wallboard: