1 · Site Prep & Storage
Acclimation
— 48 hr on-site before install. Building interior, 40–80°F, < 70% relative humidity.
Storage
— Panels flat, indoors, off the ground. Never stacked on edge. Keep factory wrapping intact until install.
Subfloor tolerance
— Substrate must be flat to ≤ 3/16″ over any 10 ft span. Shim or plane the deck before laying panels.
2 · Layout & Fastening
Run orientation
— 48″ panel dimension perpendicular to joists. Stagger T&G joints — avoid four-corner stacks.
Expansion gap
— Maintain 1/8″ gap at all perimeter walls. Do not rigid-fill.
Fasteners
— Structural screws or ring-shank nails: 6″ OC at perimeter, 8″ OC in field. Countersink 1/4″ below finish.
T&G adhesive
— PVA applied in the T&G channel before each joint. Wipe squeeze-out before cure. 24 hr cure prior to loading.
3 · Edge & Penetration Sealing
Perimeter
— Closed-cell foam backer rod at the 1/8″ gap, then flexible sealant over it. Thermal expansion requires flex.
T&G joints
— PVA in the channel at install; sealed at the field surface once cured.
PEX penetrations
— Intumescent caulk at the penetration. Add a grommet if passing through a sharp metal edge.
Manifold penetrations
— Rated wall seal per local code (UL listing varies by jurisdiction).
Field-cut for plumbing / electrical
— Not allowed through the panel. Factory-set routing only. Coordinate with ThermaSlab engineering before any field cut.
4 · Concrete Subfloor (Where Applicable)
When ThermaSlab panels are installed OVER a poured slab (slab-on-grade retrofit or basement reno), the slab below must be cured and dry before panel lay-down. This section is informational; not applicable to platform-framed installs.
| Compressive strength | 4,000 psi minimum |
| Water–cement ratio | 0.45 max |
| Aggregate size | ≤ 3/4″ |
| Cure time before panel install | Minimum 28 days |
| Moisture verification (ASTM F1869) | Calcium chloride ≤ 3.0 lb / 1000 ft² / 24 hr |
| Moisture verification (ASTM F2170) | In-situ RH ≤ 75% |
| Moisture barrier | 6 mil polyethylene, seams overlapped 6″ and taped |
5 · Hydrostatic Test & Commissioning
Pressure test
— Pressurize PEX circuits to 100 psi, hold 30 minutes. Inspect manifolds and joints for any pressure drop.
Flush before fill
— Flush the system with clean water after the pressure test, before final fill and balancing.
Initial heat-up ramp
— Supply water ≤ 80°F for the first 24 hours, then ramp 10°F/day to design temp. Prevents thermal shock to gel-cushion chambers + aluminum plates.
Zone valves
— Confirm each zone valve opens and closes on call before closing up walls. Photograph the manifold record.
6 · Finish Options & Crew Protection
The 8 factory-applied finishes (Marble, Golden Oak, Norwegian Maple, English Walnut, Provincial Oak, Brazilian Pecan, Colonial Cherry, Raw Pine) are NOT site-finished. Treat the surface like a prefinished hardwood floor from the moment of delivery.
Surface protection
— Cover with breathable rosin paper or Ram Board during construction. No tape directly on the finish surface.
Wet trades
— No wet trades (drywall mud, paint, thinset) above finished panels until floor is fully protected.
Heavy loads
— Move dollies, drywall carts, and toolboxes over 1/2″ plywood runners. No direct rolling loads on the panel.
Final walk-through
— Confirm no dropped fasteners, no scratches, no standing water > 30 minutes on the surface. Photograph for the punch list.
Three "Do Not" Items — Crew Reminders
Do Not Rigid-Fill
The 1/8″ perimeter expansion gap must remain flexible — closed-cell backer rod + flexible sealant only. Rigid filler will crack and split the finish as the panel expands.
Do Not Field-Cut PEX Lanes
PEX routing is factory-set into the gel-cushion chambers. Field cuts destroy the radiant field. Plumbing and electrical must run around or beneath the panel.
Do Not Ramp Above 130°F
Supply water on first heat-up must stay at or below 80°F for 24 hours, then ramp 10°F/day. Shock-ramping above 130°F stresses the gel-cushion seal and aluminum plates.
Questions during install?
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