How to "mount" acoustic foam ?


My main system is in my partially unfinished basement.
While I have finished the ceiling and have nice floors / rugs - I do like the industrial / rough look of the concrete walls....I just finished painting them but don't want to install any sheetrock / finishing material.
Instead I want to buy acoustic foam (2inch depth squares) and mount them to the walls - front / back and sides
And here are my questions:
1. Should I just use glue and apply the foam squares directly to the wall ?
 - IF YES - what glue should I use? I know there is the special construction glue for laying floors etc..... I now they sell it also for concrete and stone application - sold in caulk like tubes 
2. Should I first apply the foam  to a plywood / wood and anchor that to the floors ?
 - IF YES - I would imagine a few concerns: 
-  Will that wooden structure bring about sound resonance that I am actually trying to control ? (Wood isn't as bad as concrete but still....) 
-  Will I have to add a layer of caulk or similar filler between the wall and  the wooden panel? Obviously the concrete walls are not super smooth so the wood panels will not be in perfect and uniform contact. They will be held rigid with the specialty screws drilled into the walls....but still 
- What type of panels should I use....I was thinking anything from very thin cardboard like materials (to minimize any resonance from wood) to 1/2 inch plywood for rigidity.
IN SUMMARY: 

 I am leaning for the 1/8inch thick boards - In my mind it would provide smooth surface to mount the foam onto, retain the acoustic profile of the foam, and then just hold it all in place up on the wall with 4 bolts (each corner)

Anyhow....Any other tips and advice about proper installation would be appreciated.

Thank you!! 
ether
One reason for not using foam is that some of it decomposes over time, turning into a crumbling, sticky mess. I've used in in rehearsal spaces in the past, but no more. Owens Corning 703 or equivalent in wooden frames is relatively cheap; that's what all the products from GIK and the others contain. The professionally made sound panels are reasonably priced, but the shipping will kill ya.
One reason for not using foam is that some of it decomposes over time, turning into a crumbling, sticky mess.
True, if time is measured in eons, figuratively speaking. Everything decomposes over time.
 
mapman
GK,

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>>>>>mapman the comedian. 🤡
Hey now! gdhal
not laughing at you, friend. I, too, enjoy the GD especially the live offerings.
Very fine music to demo any system.
Happy Listening!
Back to original question. I suggest not affixing items to your concrete wall. Messy and make placement experimentation (tuning) challenging. Instead mount whatever you wish to try on old fashioned economical fibreboard pegboard. Drill small holes in the concrete for the tiny nails that will suffice to hold your item. There are translucent twines-think fishing line- that will not be obvious. Now you can experiment like a pro- and get the results that satisfy you. Mix,match,move,enjoy.