We recently purchased a home which had a radiant retrofit in the basement approx 10 years prior. Our first winter (last) I noticed some mold showing through the finished flooring (4' x 8' wheat board). Long story short, I found 2 screws had pierced the pex and slowly corroded over the years finally leaking and ruining it all.
The layout was 6" wide 3/4" hardboard sleepers glued and nailed to the slab with 1/2" pex between. Over the pex and sleepers, 12" wide aluminum flashing was stapled and then finish flooring. The slab is insulated (supposedly with 2 layers of 2" polystyrene under the slab). Here's a picture of the layout before.
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I ripped it all out and now am looking for the best practice in rebuilding. I am considering slightly narrower sleepers with concrete or SLC over the pex and in between the sleepers and then installing finished flooring. It seems like this would allow heat to transfer better to the slab than the way it was before. I don't want to add any more height than 3/4" sleeper and 3/4" finished floor.
What is the best way to do this? Is my plan solid and if so what material should be used for the sleepers and concrete in between, SLC or deck mud? Or something else? I wouldn't mind pouring a 1.5" slab with embedded radiant and then polishing as a finish floor but this seems expensive and a nightmare in a finished room.
Thank you for your advice!!