Heat — underfloor hydronic / ducted

Timber over underfloor heating needs to cope with a continuous dry-heat load and a predictable seasonal gap cycle. Engineered boards on a matched-conductivity substrate with a controlled surface temperature and a waterborne topcoat is the usual answer. Solid T&G over hydronic is not a default choice.

Mechanism

WoodSolutions TDG-09 (Timber Flooring) and ATFA Specification both emphasise that floors must be acclimatised to their in-service environment before finishing — continuous-heat environments sit at the low end of the EMC range year-round, enlarging winter gaps. Bona Traffic HD TDS notes application between 18–25°C and 30–60% RH; high temperatures and low humidity shorten drying times but can cause excessive wood swelling if more than two full coats are applied per day, so the practitioner must plan coats around the heating schedule.

Risk profile by species

SpeciesRiskNote & source
Engineered Multi Ply preferred-for-uhf Cross-ply construction reduces dimensional response to the heat-driven EMC cycle.Source: atfa-specification-for-solid-timber-flooring-installation-sanding-and-coating.pdf (prefinished solid vs engineered framing p.1, 6.0)
Solid Tg 19mm case-by-case Solid 19 mm T&G on joists/battens is covered by ATFA spec; requires fastener + adhesive control, and hydronic under solid is not a default Australian detail.Source: atfa-specification-for-solid-timber-flooring-installation-sanding-and-coating.pdf p.72

Mitigations

  • Set the heating system to a stabilised mid-range temperature for at least 72 hours before, during and after floor install (industry practice referenced in ATFA spec).
    Source: atfa-specification-for-solid-timber-flooring-installation-sanding-and-coating.pdf
  • traffic-hd
    Apply Bona Traffic HD at 18–25°C surface temperature, 30–60% RH. Minimum temperature for use is 13°C. High temperature + low humidity shortens drying; do not apply more than two full coats of primer and/or lacquer per day.
    Source: Bona_TrafficHD_TDS_AU.pdf p.2 – 'PREPARATION' + TREATMENT SCHEDULE notes
  • r540
    Use a moisture vapour barrier on slab installs even when the heating is on; the slab itself can hold moisture longer than an air-dry test would suggest.
    Source: backup__Bona_R540_Specifier_Paragraphs.txt
  • Keep floor surface temperature within the flooring manufacturer's stated maximum. ATFA spec requires an acclimatised in-service environment — measure RH and temperature at board level, not in the ceiling void.
    Source: atfa-specification-for-solid-timber-flooring-installation-sanding-and-coating.pdf

Bona product guidance

  • traffic-hd
    2-component waterborne topcoat rated for commercial floors; application window 18–25°C / 30–60% RH; min temperature 13°C. Pot life 4 hrs at 20°C (shorter if warmer).
    Source: Bona_TrafficHD_TDS_AU.pdf p.2
  • craft-oil-2k
    Oil-catalysed penetrating finish. Heavy commercial build: 1 x Bona Craft Oil 2K. Moderate/high traffic build: 2 x Bona Craft Oil 2K. Acclimatisation still required before application.
    Source: Bona_Craft_Oil_2K_TDS.pdf p.4

Gaps in the corpus (no claim made)

  • No Bona-published explicit surface-temperature ceiling for Traffic HD or Craft Oil 2K under in-service use (only application conditions are published).
  • No ATFA position paper specifically on hydronic-under-solid-T&G in the pulled corpus.
Sources