Radiant Barrier for Slump Block wall

I have a slump block wall which is bare on the inside and outside of the house. This wall faces the South and during the hot Arizona Summers, the rooms that share this wall get very hot that is about 20 degrees F or so more than the rooms that are on the North side.
Last year I had the core of the blocks filled with some form-like material but that does not appear to help much once the temperature goes over 100 deg. F.
Is there some kind of radiant barrier paint perhaps in clear color that can be applied on the inside and outside of the wall? I am suggesting paint as the first option because it is something I can do myself.
If paint is not a good then what are the alternatives for reducing the temperature in those rooms without losing the looks of the slump block?
Thanks for any tips?
James
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I had my slump block home injected with a foam and it made a tremendous difference. My garage wall, slump inside and out was noticeably cooler after the foam was installed. Summer sun facing west was the orientation. There were days that is was almost painful to touch the slump block on the outside and the inside was close to ambient. The only thing I can think of is to furr the inside, insulate and drywall. Beats me why anyone would want a slump block interior wall. Ya I had 2 and hated them.
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