A. Michael Byrne responds: Renovating a barn slab is riskier than farming. A host of unseen problems, from poor drainage to inadequate reinforcing, could seriously affect the life of the slab you pour on top. It would be bad enough if the topping pour were close to level, but the wedge you are planning is bound to be problematic.
Whenever the substrate and subsoils are in doubt, as they are in your case, no isolation membrane will protect the tiles or the radiant heat system. Tapered pours are notorious for cracking because concrete and mortar have greatest strength when their cross-sections are uniformly thick. Also, it will be difficult to secure the hydronic tubing in...
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