How to bond ThermalSheet™ insulating underlayment to a concrete slab under floor heating, and which finished-floor assemblies are documented over it.
WarmlyYours no longer sells CeraZorb® underlayment. ThermalSheet™ (TS-SH6MM-24x36) replaces it: one 2 × 3 ft sheet, 6 mm (15/64 inch) thick, covering 6 sq ft, with an R-value of 1.5. It is recommended under TempZone™ and Environ™ floor heating over a concrete slab, as a thermal break that keeps heat from sinking into the concrete. Older TempZone cable manuals mention a 5 mm sheet; the current ThermalSheet is 6 mm.
Prepare the slab
- The slab must be structurally sound, fully cured, clean, dry, smooth and flat, free of efflorescence and not under hydrostatic pressure.
- Fill open cracks with a high-grade patch and remove lumps or residue that would interfere with the bond.
- If moisture in the slab is above 10 percent, a concrete waterproof sealer may be required.
- Acclimatize ThermalSheet in its sealed packaging for 48 hours at 65°F (18°C).
Bond the sheets
- Use a high-quality modified thinset with a 1/8 × 1/8 × 1/16-inch V-notch trowel, or Armstrong S-235 or Roberts 6700 bond-coat adhesive with a 1/16 × 1/16 × 1/16-inch square-notch trowel. The material and slab must be at least 65°F (18°C).
- Spread only enough for one sheet, set the sheet while the material is wet, and lift a corner to check for 100 percent transfer.
- Butt the edges tight without overlapping, roll each row with a 50 lb roller and stagger the seams of the next row.
- Wait 8–12 hours before installing tile or stone.
Finished-floor assemblies
- Tile, stone or marble: TempZone heating set in polymer-modified thinset over the bonded ThermalSheet. Use mortar meeting ANSI A118.4 or A118.11, and key a thin layer of thinset into the sheet first.
- Luxury vinyl tile: WarmlyYours cross-sections show TempZone Cable or a TempZone mat embedded in 1/2 inch of primed self-leveling cement over the bonded ThermalSheet, with the vinyl on top. They do not show vinyl laid directly on ThermalSheet. Confirm the vinyl manufacturer approves its product over floor heating.
- Floating wood or laminate with Environ: ThermalSheet can float instead of being bonded; see How to Install ThermalSheet Under A Floating Floor.
Install a single layer; see Can ThermalSheet underlayment be installed in multiple layers?
Sources: ThermalSheet installation instructions, pages 1–2; ThermalSheet sell sheet; ThermalSheet data sheet; TempZone Cable LVT over concrete cross-section; TempZone Mat LVT over concrete cross-section.
